UNIVERSITY OF CALIFORNIA 
 
 COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION 
 
 BERKELEY, CALIFORNIA 
 
 MATURITY TESTS FOR 
 TABLE GRAPES 
 
 A. J. WINKLER 
 
 BULLETIN 529 
 
 June, 1932 
 
 UNIVERSITY OF CALIFORNIA PRINTING OFFICE 
 BERKELEY, CALIFORNIA 
 
MATURITY TESTS FOR TABLE GRAPES 
 
 A. J. WINKLER2 
 
 The numerous tests and examination of table grapes made in 
 efforts to ascertain the proper stage of maturity at which they should 
 be picked have dealt primarily with the chemical composition of 
 the fruit. Except for the work of Bioletti and Zion, as reported by 
 Bioletti, 3 little or no attempt has been made to determine directly 
 the correlation between the palatability — eating quality — of the 
 analyzed fruit and its chemical components such as sugars or acids. 
 Bioletti and Zion attempted to discover how far the sugar content 
 as measured by a hydrometer and expressed as degrees Balling of the 
 expressed juice, could be relied upon to indicate the eating quality 
 of the grapes and what advantage there would be in the substitution 
 or addition of the acid test or of the sugar : acid ratio. Their con- 
 clusion was that the Balling hydrometer test is the simplest and 
 most reliable that can be used practically in determining the degree 
 of ripeness of grapes for the purpose of standardization. According 
 to their data the Emperor was good when it reached 19° Balling, the 
 Malaga and Tokay when they reached 21° Balling, and the Thompson 
 Seedless (Sultanina) when it reached 18° Balling. 
 
 The degrees Balling indicated by Bioletti and Zion for the varieties 
 included in their work, however, have not been accepted by the 
 growers, presumably because they have been considered to be too 
 high. This difference of opinion together with the lack of informa- 
 tion which has confronted the grape growers each time the Standard- 
 ization law of 1915 has been amended, expanded, or contracted, shows 
 the need of a better method of determining the minimum stage of 
 maturity at which table grapes should be harvested. This need of a 
 better method of determining maturity has been increased on the 
 one hand by a desire on the part of many growers to improve quality 
 and on the other hand by a continued insistence on the part of a 
 few growers to move their fruit as early as possible, regardless of 
 whether or not it has reached a stage of maturity which is satisfactory 
 to the consumers. 
 
 i Received for publication April 12, 1932. 
 
 2 Associate Professor of Viticulture and Associate Viticulturist in the Experi- 
 ment Station. 
 
 3 Bioletti, F. T. The basis of grape standardization. California Agr. Exp. Sta. 
 Cir. 293:1-16. 1925. 
 
4 University of California — Experiment Station 
 
 In an attempt to discover evidence which might help to overcome 
 some of the difficulties of determining the stage of ripeness at which 
 grapes should be harvested, the Division of Viticulture began a gen- 
 eral investigation of the maturity of table grapes in 1927. It was 
 our purpose to determine (1) the factors of composition of the grape 
 which exert the greatest influence on palatability, (2) the influence 
 of variety upon the relation of composition to palatability, (3) the 
 influence of regional and seasonal conditions upon composition and 
 palatability, and finally, (4) the possibility of establishing a more 
 satisfactory means of determining maturity in relation to palatability 
 than the present one of measuring only the degree Balling of the 
 expressed juice. 
 
 METHOD OF PROCEDURE 
 
 The method of procedure was similar to that employed by Bioletti 
 and Zion, the principal differences being that all samples were scored 
 for eating quality by six or more individuals instead of only three or 
 more and that all samples were scored by a group of individuals 
 residing in Davis. The larger number of scorers represented better 
 the taste of the average consumer and being unconnected with the 
 locality where the grapes were grown were free from any unconscious 
 bias in favor of a product of their own locality. 
 
 Collection of Samples. — During 1927 and 1928, while the methods 
 of scoring and analysis were being tested, the collection of samples 
 was confined to the table grape varieties in the University Farm 
 vineyards at Davis. Each day during the harvesting season one lot 
 of twelve samples was collected so as to represent a range of ripeness 
 from well below what would be considered fair in eating quality to 
 what would be considered good to excellent. Each lot was composed 
 of a single variety. The individual samples of a lot represented 
 approximately five pounds of grapes of as nearly the same degree 
 of ripeness as it was possible to obtain by tasting each cluster before 
 it was removed from the vine. In the seasons of 1929, 1930, and 1931 
 samples of the leading table grape varieties in the ripening range, 
 i.e. from poor to good in eating quality, were also collected from 
 all of the principal districts of the state in which they are grown. 
 In these collections usually only one lot, and at most two lots, of 
 twelve samples of one variety were obtained from one grower. Six 
 or more lots of each variety were obtained in each of the principal 
 districts. By collecting only one lot of a variety from a ranch and 
 obtaining fruit from as many locations in a district as possible, fruit 
 which was fairly representative of the district was obtained. 
 
Bul. 529] Maturity Tests for Table Grapes 5 
 
 After collection, the samples were immediately shipped to Davis 
 by express and stored at 30° F until the day before they could be 
 scored and analyzed. The fruit was always brought to room tempera- 
 ture for the scoring. In no case was the storage period sufficiently 
 long to result in any appreciable changes in the quality of the fruit. 
 The samples from the University Farm vineyards were scored and 
 analyzed on the day they were collected. 
 
 Scoring the Samples. — The samples of one lot of fruit were placed 
 at random on a table and numbered from one to twelve. The indi- 
 vidual scorers then tasted a sufficient number of the berries from 
 various parts of the clusters of each sample to enable them to designate 
 its eating quality as poor, fair, good, very good, or excellent. Of the 
 total group of 43 individuals that cooperated in the scoring at least 6 
 and usually not more than 8 tasted each sample of a lot of fruit. 
 Each of the individuals scored the samples of fruit independently. 
 This method of scoring along with the fact that only one lot of 
 fruit was scored on one day which was not enough to deaden the 
 power of discrimination of the tasters, resulted in a fairly accurate 
 evaluation of the relative eating quality of the samples. That this 
 was true is indicated by the precision with which the poor samples 
 are separated from the good in the tables presented in connection with 
 the discussion of the Balling-acid ratio as a means of measuring 
 palatability. 
 
 To make it possible to average scores, the terms used to designate 
 eating quality were given a numerical value. The scoring for one 
 lot of fruit and the average numerical scores for each sample are 
 shown in table 1. 
 
 Analysis of the Samples. — After scoring, the samples collected in 
 1927 and 1928 were pressed and the juice analyzed to determine its 
 sugar content, pH, and acidity. The sugar content was determined 
 by chemical means, with a refractometer, and by the Balling 4 hydro- 
 meter. Each of the samples was passed through a motor-driven 
 continuous press to express the juice. While this method of pressing 
 did not remove all of the juice it resulted in a uniform extraction so 
 that the expressed juice was representative of the sample of fruit 
 used. After pressing, the juice was placed in tall beakers and left 
 standing for a time to allow any suspended solid material to settle. 
 When the settling out was very slow, this material was removed by 
 straining through several layers of cheesecloth or by centrifuging. 
 
 4 The Balling hydrometer scale is for all practical purposes the same as the 
 Brix scale. 
 
6 University of California — Experiment Station 
 
 For the chemical analysis the juice was clarified with neutral 
 lead acetate and the excess lead removed with potassium oxalate; the 
 sugar reductions were carried out according to the Schaffer-Hartman 5 
 method. The refractometer determination of the sugar was made with 
 a laboratory type Abbe refractometer. For the determination of 
 degrees Balling see the next section. 
 
 The two methods of determining the sugar in addition to the 
 Balling degree reading were used in order to determine the relative 
 accuracy with which the sugar content in the juice is measured by 
 the three methods. Since Balling degree is a measure of the specific 
 
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 Fig. 1. — A comparison of the results obtained on expressed grape juice by- 
 means of the Balling hydrometer, the refractometer, and chemical analysis. 
 
 gravity which is influenced by all of the soluble solids, the question 
 has arisen in the minds of many growers as to whether or not it is 
 a reliable measure of eating quality, which is probably influenced 
 more by the sugar content of the grapes than by any one of the other 
 constituents. Figure 1 shows the results obtained with the three 
 methods, using 378 samples which were regularly distributed among 
 eight varieties and over the range of 14.5° to 24.5° Balling. 
 
 The graphs showing the results obtained by the three methods 
 are fairly concordant and indicate that each might be used as a guide 
 
 5 Shaffer, P. A., and A. F. Hartman. The iodometric determination and its 
 use in sugar analysis. Jour. Bio. Chem. 45:349-390. 1920. 
 
Buu 529] Maturity Tests for Table Grapes 7 
 
 for standardization. The hydrometer and refractometer readings are 
 very close together; the greater difference of the chemical analysis is 
 due to the fact that it measures only the sugar, while the others are 
 affected by nonsugar solids as well. The apparent irregularity of the 
 graph of chemical analysis is due to the fact that the Balling readings 
 have been used as the standard by which the division of grape samples 
 into groups was made, and the Balling line is thus straight by con- 
 struction. The irregularities in the other lines indicate simply devia- 
 tions between the three methods, and do not necessarily indicate that 
 any has an advantage over the others. 
 
 The results presented in figure 1 are confirmed by those of other 
 workers. 6 This is true both for the relatively small error of the Ball- 
 ing readings and for the greater irregularity in the results of an 
 analysis for sugar by chemical means. 
 
 In the case of mature, and approximately mature, vinifera table 
 grapes it would seem, therefore, that degree Balling gives a very 
 accurate relative measure of the sugar content of the expressed juice. 
 It may without question be accepted as the most practicable means 
 of determining the sugar content of grape juice under field conditions. 
 It is to be recommended over the refractometer because the latter 
 requires very small quantities of juice. Only one or two drops can 
 be used for a determination. Working with such small amounts of 
 juice, which may be obtained from a single berry, the error of 
 sampling may be very large. 
 
 In view of the above results on the determination of the sugar 
 content of the expressed juice and to facilitate the work, Balling 
 degree readings alone were taken after the 1928 season. 
 
 Balling Degree. — The cleared juice as obtained b}^ settling or 
 straining was poured into a tall glass cylinder, the cylinder being 
 always filled to overflowing so that the foam, which formed when the 
 juice was poured in, ran off. A Balling or Brix hydrometer was then 
 carefully placed in the filled cylinder. When the instrument came 
 to rest, the reading on the spindle at the surface of the liquid was 
 recorded and also the temperature of the juice. 
 
 Hydrometers, calibrated to 0.1 per cent of sugar at 63.5° and 
 82.5° F were used. A correction was made for any variation from the 
 calibration temperature. This temperature variation 7 is about 0.1° 
 
 6 Bioletti, F. T., W. V. Cruess, and H. Davi. Changes in the chemical com- 
 position of grapes during ripening. California Pub. Agr. Sci. 3:103-130. 1918. 
 
 7 Official and tentative methods of analysis of the Association of Official 
 Agricultural Chemists. Published by the Association of Official Agricultural 
 Chemists, Washington, D. C. 2nd Ed. p. 428. 1925. 
 

 8 University of California — Experiment Station 
 
 Balling for every 3° F above or below the calibration temperature of 
 the instrument used. 
 
 Acidity. — In determining" the acidity 10 cc of the clear juice was 
 pipetted into a 300 cc Erlenmeyer flask and made up to approxi- 
 mately 100 cc with distilled water. After adding 3 drops of 
 phenolphthalein indicator, the titration was made with sodium 
 hydroxide which had been standardized so that 1 cc was equivalent 
 to 0.01 gram tartaric acid. Care was exercised to stop the titration 
 at the first definite color change. While it is realized that the titra- 
 tion of grape juice against phenolphthalein gives results which are 
 high, no other indicator which could be used in the field gave more 
 accurate results. 
 
 It is essential that only clear juice, i.e., juice free from fiber and 
 other solid parts of the berry which come through in pressing be 
 used in the acidity determinations. Failure to use clear juice gave 
 results which were 10 to 100 per cent too high. This was owing 
 probably to the tannin content of the fibrous material which reacts 
 with the sodium hydroxide. 
 
 Determinations for pH were made on the clear juice in 1927. The 
 change in the pH of the expressed juice of grapes as they developed 
 from the stage of being almost mature to full maturity (say 16° to 22° 
 Balling) was small. There was no clear-cut relation between pH and 
 eating quality. 
 
 Scope and Nature of the Data. — During the seasons of 1927 to 
 1931, inclusive, data similar to those shown for the twelve samples of 
 table 1 were collected for 3,680 samples. This number of samples was 
 distributed among the varieties used as follows: Thompson Seedless 
 (Sultanina), 875; Malaga, 760; Tokay, 492; Emperor, 460; Ribier, 
 325; Molinera (Red Malaga), 260; Muscat, 200; Ohanez (Almeria), 
 120 ; Cornichon, 72 ; Rish Baba, 68 ; and Olivette Blanche, 48. The 
 large numbers of samples of Thompson Seedless and Malaga as com- 
 pared with the other varieties were used because of the wide dis- 
 tribution of these two varieties. They are grown under more varied 
 climatic conditions than all of the other varieties combined. 
 
 After the preliminary tests which showed that it would be injudi- 
 cious to continue with certain of the determinations, the data col- 
 lected for each sample consisted of the score for eating quality, the 
 degree Balling, and the per cent acidity of the expressed juice. The 
 Balling-acid ratio was calculated from the degree Balling and the per 
 cent acidity. A complete record for a single lot of fruit is shown 
 in table 1. 
 
Bul. 529] 
 
 Maturity Tests for Table Grapes 
 
 The scores shown in table 1 indicate the nature of the scoring. 
 Even in this very limited number of samples, the individuality of 
 the tasters is reflected. Scorer 1, for instance, marked all of the 
 samples with one exception, as low or lower than anyone else, while 
 scorer 4 marked each of the samples as high or higher than anyone 
 else. The opinions of scorers 3, 5, and 6 were in close agreement and 
 scorer 2 marked the samples only a bit more severely. Such differ- 
 ences as these are to be expected since no two individuals have identi- 
 cal tastes. The relative placing of the samples also varied from day 
 to day, apparently being influenced by the health and disposition of 
 the scorer at the time the scoring was done. 
 
 TABLE 1 
 
 The Scoring, the Numerical Score, and the Analytical Data for One Lot 
 of Thompson Seedless (Sultanina) 
 
 
 
 Scorers with their scores 
 
 
 Average 
 
 
 Per cent 
 
 Ball- 
 
 Sam- 
 
 
 
 
 
 
 
 numeri- 
 cal 
 
 Degree 
 Balling 
 
 acid, 
 
 as 
 
 ing — 
 
 ple 
 
 
 
 
 
 
 
 acid 
 
 Mo. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 score* 
 
 
 tartaric 
 
 ratio 
 
 1 
 
 Fair - 
 
 Poor 
 
 Fair 
 
 Fair 
 
 Fair — 
 
 Fair 
 
 18.1 
 
 15.6 
 
 93 
 
 17 
 
 2 
 
 Poor 
 
 Poor + 
 
 Good- 
 
 Fair + 
 
 Poor + 
 
 Poor + 
 
 16.5 
 
 15.4 
 
 91 
 
 17 
 
 3 
 
 Good- 
 
 Good 
 
 Good 
 
 Good + 
 
 Good 
 
 Good- 
 
 48.7 
 
 20 4 
 
 74 
 
 28 
 
 4 
 
 Fair 
 
 Fair 
 
 Good- 
 
 Good 
 
 Good- 
 
 Good- 
 
 38.2 
 
 18.8 
 
 0.72 
 
 26 
 
 5 
 
 Fair + 
 
 Fair + 
 
 Good 
 
 Good 
 
 Fair -f- 
 
 Good 
 
 41.5 
 
 20.2 
 
 0.73 
 
 28 
 
 6 
 
 Good- 
 
 Good 
 
 Good 
 
 Good 
 
 Good 
 
 Good 
 
 48.7 
 
 20.9 
 
 0.67 
 
 31 
 
 7 
 
 Poor 
 
 Poor 
 
 Fair 
 
 Fair 
 
 Poor 
 
 Fair — 
 
 11.2 
 
 14.2 
 
 95 
 
 15 
 
 8 
 
 Fair 
 
 Good- 
 
 Fair 
 
 Good- 
 
 Fair — 
 
 Fair 
 
 29.4 
 
 16.4 
 
 87 
 
 19 
 
 9 
 
 Fair — 
 
 Fair — 
 
 Fair — 
 
 Fair 
 
 Fair — 
 
 Fair — 
 
 18 3 
 
 14.1 
 
 90 
 
 16 
 
 10 
 
 Good 
 
 Very good 
 
 Good + 
 
 Very good 
 
 Good 
 
 Good + 
 
 61 
 
 21 
 
 0.67 
 
 31 
 
 11 
 
 Fair 
 
 Fair 
 
 Fair 
 
 Good + 
 
 Fair 
 
 Fair 
 
 30 5 
 
 17.0 
 
 0.85 
 
 20 
 
 12 
 
 Good- 
 
 Good + 
 
 Good 
 
 Good 
 
 Good - 
 
 Good 
 
 48.7 
 
 19 3 
 
 0.70 
 
 28 
 
 'Numerical values of the scores: Poor=0; fair=25; good=50; very good=75; and excellent=100. 
 A plus (+) or minus (— ) =8. 
 
 Some of the differences in the scoring were also due to the 
 difference in the maturity of the individual berries on the clusters. 
 Although great care was exercised in selecting the fruit for each 
 sample, yet it was obviously impossible to have all of the clusters and 
 berries of one sample of identically the same stage of maturity. It 
 was obviously impractical to have the different scorers taste parts 
 of the same berries, hence no two scorers were tasting identical 
 berries. Such variances from the other scores as that given by 
 scorer 4 on sample 11 were, no doubt, owing to the fact that this 
 scorer tasted berries which were far above the average in quality for 
 the sample. 
 
10 University of California — Experiment Station 
 
 Despite these influences the accuracy of the scores may be con- 
 sidered sufficient for the purpose of classifying' the samples. There 
 is all reason to believe that they are equal if not superior to any which 
 could be obtained by other means. Where a sufficient number of 
 samples were scored by the same group of individuals to permit of 
 statistical treatment the greatest difference between scorers for the 
 same samples was only about 5 per cent. 
 
 THE INFLUENCE OF REGIONAL CONDITIONS ON THE DEGREE 
 
 BALLING, PER CENT ACIDITY, AND PALATABILITY 
 
 OF GRAPES 
 
 The influence of regional conditions upon the eating quality of 
 grapes has been recognized in a general way for many years. In 
 fact, it was incorporated in the California Standardization law until 
 1931. Sufficient figures to prove the definite relation with palatability, 
 however, have been lacking. 
 
 The Influence of Regional Conditions on Composition. — In com- 
 paring the influence of regional conditions on the composition of the 
 fruit, samples were obtained from the following regions: (1) Coa- 
 chella and Imperial valleys, (2) Kern County, and (3) the region 
 from Fresno to Davis, The first of these regions is typical of the hot 
 arid desert. The region Fresno-to-Davis is considerably cooler than 
 the first named in that it is subject to the influence of the ocean 
 breezes that come in from the San Francisco Bay region. Kern 
 County is intermediate. 
 
 The process of ripening in the grapes is a continuous one. This 
 being the case, there is no maximum in the sugar content nor mini- 
 mum in the acid content at which a grape can be said to be ripe. The 
 relative rates in the change of these substances also influences the 
 time at which the fruit becomes palatable. A rapid decline in acidity 
 may result in the fruit becoming palatable at a relatively low sugar 
 content. On the contrary, a rapid accumulation of sugar with a slow 
 decline in acidity may result in the development of fruit which is 
 palatable at a very high acid content because its sugar content also 
 is high. Palatability is influenced not only by the quantity of each 
 of these substances in the fruit but also by their relation to one 
 another. 
 
 For the purpose of comparing fruit of one region with that of 
 another it is necessary to employ some definitely measurable factor 
 as a basis. For this purpose both the degree Balling and the per 
 cent acidity have been employed. The regional influence on the degree 
 
Bul, 529] 
 
 Maturity Tests for Table Grapes 
 
 11 
 
 Balling of grapes of the same per cent acidity is shown in table 2. 
 This same influence on the per cent acidity and the relation of the 
 sugar to the acid content of the fruit of the same degree Balling is 
 shown in table 3. 
 
 TABLE 2 
 
 The Influence of Regional Conditions on the Degree Balling of Grapes of 
 
 the Same Acid Content 
 
 Variety 
 
 Thompson] 
 Seedless ] 
 
 Malaga 
 
 Coachella and Imperial 
 
 valleys 
 
 Kern County 
 
 Fresno-to-Davis 
 
 Coachella and Imperial 
 
 valleys 
 
 Kern County 
 
 Fresno-to-Davis 
 
 Per cent acid 
 
 0.55 to 
 0.60 
 
 0.60 to 
 0.65 
 
 0.65 to 
 70 
 
 0.70 to 
 75 
 
 0.75 to 
 0.80 
 
 Degree Balling 
 
 18.4 
 
 18.5 
 
 0.80 to 
 0.85 
 
 0.85 to 
 0.90 
 
 18.6 
 
 18 
 
 18 5 
 
 18.0 
 
 
 19.4 
 
 19 8 
 
 19.3 
 
 19 
 
 18.9 
 
 
 21.8 
 
 21 5 
 
 21.9 
 
 21 5 
 
 18.1 
 
 18 5 
 
 18 3 
 
 18.5 
 
 
 19 3 
 
 19 4 
 
 19 6 
 
 198 
 
 18.7 
 
 
 21.6 
 
 21 3 
 
 21 4 
 
 20 7 
 
 20 4 
 
 The figures of table 2 show the influence of the conditions of the 
 three regions on palatability rather than the relation which existed 
 between degree Balling and acidity during normal ripening in these 
 regions. Usually grapes of high acidity would be relatively low in 
 sugar and those of low acidity would have a relatively high sugar 
 content. Since the samples were collected by taste so that they would 
 fall within a relatively narrow range of palatability from just below 
 what would be considered fair in eating quality to what would be 
 considered good this normal relation of degree Balling to acidity 
 was almost completely upset. The relation of acidity to eating quality 
 was not disturbed by this method of sampling. Of the fruit collected 
 in the Coachella and Imperial valleys 100 per cent of the samples of 
 0.55 to 0.60 per cent acidity were scored fair or better by the tasters, 
 while only 33 per cent of the samples of 0.75 to 0.80 per cent acidity 
 were scored fair or better. A similar relative influence of acidity on 
 eating quality was shown by the sample of fruit from the other 
 regions. 
 
 Samples collected in this way, however, clearly show the influence 
 of regional conditions on eating quality. In the Thompson Seedless 
 the Balling reading of the fruit of the Fresno-to-Davis region was 
 
12 
 
 University of California — Experiment Station 
 
 2.4° higher than that of Kern County and 3.3° higher than that of 
 the Coachella and Imperial vallelys region, The fruit of Kern 
 County was 0.9° Balling higher than that of Coachella and Imperial 
 valleys. For the Malaga the samples of the Fresno-to-Davis region 
 were 2.7° Balling higher than those of Coachella and Imperial valleys 
 and 1.7° Balling higher than those of Kern County. In this variety 
 the samples from Kern County were 1.0° Balling higher than those 
 from the Coachella and Imperial valleys. In other words, for the 
 fruit of the three regions to be of the same eating quality that of 
 Kern County must contain sufficiently more sugar to increase its 
 Balling reading about 1°, and that of the Fresno-to-Davis region 
 enough more to increase its Balling reading about 2.5° above that of 
 the fruit of the Coachella and Imperial valleys. 
 
 TABLE 3 
 
 The Influence of Kegional or Climatic Conditions on Per Cent Acid and 
 
 the Balling- Acid Eatio of Grapes of the Same Degree Balling 
 
 Variety 
 
 
 Degree Balling 
 
 of the 
 
 expressed 
 
 juice 
 
 Coachella 
 
 and 
 Imperial 
 valleys 
 
 Kern 
 County 
 
 Fresno-to- 
 Davis 
 
 
 Per cent acid 
 
 f 
 Thompson Seedless \ 
 
 Malaga i 
 
 17.0 to 17.9 
 18.0 to 18.9 
 19.0 to 19.9 
 
 17.0 to 17.9 
 18.0 to 18 9 
 19.0 to 19.9 
 
 73 
 70 
 0.69 
 
 0.69 
 64 
 59 
 
 80 
 0.78 
 71 
 
 0.80 
 0.73 
 69 
 
 0.85 
 82 
 74 
 
 81 
 0.77 
 71 
 
 
 
 Balling-acid ratio 
 
 
 [ 
 I 
 
 17.0 to 17.9 
 18.0 to 18.9 
 19.0 to 19.9 
 
 17.0 to 17 9 
 18.0 to 18.9 
 19.0 to 19.9 
 
 24:1 
 26:1 
 28:1 
 
 25:1 
 29:1 
 33:1 
 
 22:1 
 24:1 
 27:1 
 
 22:1 
 25:1 
 28:1 
 
 22:1 
 23:1 
 
 Malaga ' 
 
 26:1 
 
 22:1 
 24:1 
 27:1 
 
 These differences in the degree Balling at the same per cent acidity 
 may be the result of several conditions. The most generally accepted 
 theory is that the acidity of the fruit is reduced more rapidly in the 
 hotter regions. This belief is supported by the figures on acidity 
 in table 3. The difference may also result from a retarded accumula- 
 tion of sugar and a rapid reduction of the acidity in the hotter 
 
Bul. 529] Maturity Tests for Table Grapes 13 
 
 regions. This idea is supported by the fact that the sugar content 
 of the fruit in hot seasons in the hot regions never gets very high. 
 A third possible cause for this difference might be a greater accumu- 
 lation of sugar and a smaller reduction in acidity in the cooler 
 regions. It is a recognized fact that the largest accumulation of 
 sugar takes place in such regions as that of Fresno-to-Davis — the 
 coolest region considered in these comparisons. 
 
 The figures of table 3 show a decided increase in the acid content 
 of the grapes of the Kern County and the Fresno-to-Davis regions 
 over that of the Coachella and Imperial valleys region. In the 
 Thompson Seedless this increase was 16.5 per cent at 17° Balling, 
 17.1 per cent at 18° Balling, and 7.2 per cent at 19° Balling, for the 
 Fresno-to-Davis region. 
 
 In the Malaga the differences in the per cent acid for the Kern 
 County and Fresno-to-Davis regions over that of the Coachella and 
 Imperial valleys region were still greater. The increase in favor of 
 Kern County was 16.0 per cent at 17° Balling, 14.1 per cent at 18° 
 Balling, and 17.0 per cent at 19° Balling. In the Fresno-to-Davis 
 region the increase over that of the Coachella and Imperial valleys 
 region was 18.4 per cent at 17° Balling, 20.3 per cent at 18° Balling, 
 and 20.4 per cent at 19° Balling. 
 
 The above figures definitely show the influence of regional con- 
 ditions on the acidity of grapes. The differences are all clearly 
 significant when the comparisons are made between the Coachella 
 and Imperial valleys region and the other two regions. The same 
 is true of the differences for the Thompson Seedless between the 
 Kern County and the Fresno-to-Davis region. In the Malaga the 
 difference in per cent acid in the Kern County and the Fresno-to-Davis 
 regions was relatively small. This was possibly owing to the rela- 
 tively later harvesting of this variety in the latter region. This 
 longer exposure of the grapes to the conditions prevailing in late 
 summer in this region would tend to reduce the acid content. 
 
 The Balling-acid ratio shown in table 3 is simply a function of 
 degree Balling and the per cent acid. It shows the influence of 
 regional conditions on both the sugar and the acid content of the 
 grapes relative to one another. 
 
 In the Thompson Seedless the Balling-acid ratio of the fruit of 
 the Fresno-to-Davis region was 4.8 per cent at 17° Balling, 4.4 per 
 cent at 18° Balling, and 3.9 per cent at 19° Balling lower than that 
 of the fruit of Kern County. The difference between the Fresno-to- 
 Davis and Coachella and Imperial valleys regions was 14.6 per cent 
 
14 University of California — Experiment Station 
 
 at 17° Balling', 13.1 per cent at 18° Balling:, and 7.7 per cent at 19° 
 Balling". 
 
 As in the case of the per cent acidity, there was a relatively small 
 difference in the Balling-acid ratio of the Malaga for the Fresno-to- 
 Davis and the Kern County regions. The difference between the 
 Fresno-to-Davis and the Coachella and Imperial Valleys regions, 
 however, was very marked. At 17° Balling it was 12.0 per cent in 
 favor of the hot desert region. With an increase in Balling the 
 difference became even greater, so that at 18° Balling", it was 18.5 
 per cent, and at 19° Balling, 22.2 per cent. 
 
 The Balling-acid ratio not only further illustrates the influence oF 
 regional conditions on the sugar and acid content of the fruit, but 
 it appears to indicate a difference in the effect of the regional con- 
 ditions at different degrees Balling. At 17° Balling the percentage 
 difference in the Balling-acid ratio between the regions was less than 
 the difference in the per cent acidity, while the reverse is true at 19° 
 Balling'. This difference may result from a difference in the condi- 
 tions prevailing at the time the fruit was 17° Balling and when it 
 reached 19° Balling. Such conditions could hardly account for the 
 difference shown here, however, since all of the samples from a given 
 region were harvested in the course of only a few days. It would 
 seem, therefore, that the difference was owing- to the fact that the 
 riper fruit was more susceptible to the influences of climatic conditions. 
 Most growers in the very hot regions believe this to be true. 
 
 The Influence of Regional Conditions on Palatability. — The influ- 
 ence of regional conditions on the palatability of grapes can be shown 
 by comparing' the scoring of the fruit of the same degree Balling 
 from the three regions. For the Coachella and Imperial valleys region 
 and the Kern County region all of the samples that were analyzed 
 were also scored by tasting. Thus, all of the samples from these 
 regions appear in tables 2 and 3 as well as in tables 4 and 5. In the 
 case of the Fresno-to-Davis region most of the fruit was so acid at 17° 
 Balling as to be unpalatable ; hence, to obtain more representative 
 information concerning the per cent acid and the Balling-acid ratio 
 at 17° and 18° not all of the fruit from this region was scored. 
 Enough samples, however, were scored to indicate the relative eating 
 quality at the different degrees Balling. The data on the influence 
 of regional conditions on the palatability of the Thompson Seedless is 
 shown in table 4 and that of the Malaga is shown in table 5. 
 
 The figures of table 4 show that 61 per cent of the fruit from the 
 Coachella and Imperial region was considered as mature at 17° 
 
Bul. 529 
 
 Maturity Tests for Table Grapes 
 
 15 
 
 Balling. Of the fruit from the Kern County region 38 per cent was 
 scored as being mature at 17° Balling, and of that from the Fresno-to- 
 Davis region only 8 per cent was considered good to eat at 17° Balling. 
 At 18° Balling there is an increase in the per cent of mature fruit 
 from each region, so that 83 per cent of the Coachella and Imperial 
 fruit, 61 per cent of the Kern County fruit, and 37 per cent of the 
 Fresno-to-Davis fruit was scored as being good to eat. A similar 
 increase was found at 19° Balling. In the Thompson Seedless, there- 
 fore, the influence of these regional conditions on palatability has 
 amounted to about 1° Balling. That is, 61 per cent of the fruit of 
 
 TABLE 4 
 
 The Influence of Regional Conditions on the Palatability of Thompson 
 
 Seedless Grapes 
 
 Region 
 
 Number of 
 samples 
 
 Degree 
 Balling 
 
 Number 
 
 of samples 
 
 scoring 
 
 mature* 
 
 Per cent 
 
 of samples 
 
 scoring 
 
 mature* 
 
 ( 
 
 41 
 46 
 54 
 
 42 
 33 
 41 
 
 26 
 22 
 28 
 
 17 
 18 
 19 
 
 17 
 18 
 19 
 
 17 
 
 18 
 19 
 
 25 
 30 
 50 
 
 16 
 20 
 37 
 
 2 
 
 8 
 
 20 
 
 61 
 83 
 
 
 92 
 
 38 
 61 
 
 Fresno-to-Davis j 
 
 90 
 
 8 
 37 
 
 72 
 
 * Mature as used here refers to all of the fruit that was considered good to eat. It embraces the scores: 
 fair, good, very good, and excellent. 
 
 the Coachella and Imperial region was good at 17° Balling, 61 per 
 cent of the fruit from Kern County was good at 18° Balling, and 72 
 per cent of the fruit from Fresno-to-Davis was considered mature 
 at 19° Balling. 
 
 As indicated by the figures of table 5, a very high percentage of 
 the Malaga fruit from the Coachella and Imperial valleys above 17° 
 Balling was scored mature. Even at 17° Balling, 78 per cent of the 
 fruit was considered good to eat. For the Kern County region 38 
 per cent of the samples were considered palatable at 17° Balling, 57 
 per cent were good at 18° Balling, and 86 per cent were good at 19° 
 Balling. In the region Fresno-to-Davis 10 per cent of the samples 
 were mature at 17° Balling, 40 per cent at 18° Balling, and 57 per 
 cent at 19° Balling. In Kern County and the Fresno-to-Davis regions 
 
16 
 
 University of California — Experiment Station 
 
 ,the percentage of Malaga samples that were considered mature was 
 almost the same as for the Thompson Seedless. 
 
 Ribier was also collected in sufficient quantity from the Kern 
 County and the Fresno-to-Davis regions to further illustrate the 
 influence of regional conditions on palatability. In this variety all 
 of the 44 samples of 17° and 18° Balling collected in the former 
 region were considered mature. Of the 56 samples of 17° and 18° 
 Balling collected in the region Fresno-to-Davis 80 per cent were 
 scored mature. 
 
 TABLE 5 
 
 The Influence of Eegional Conditions on the Palatability of Malaga 
 
 Grapes 
 
 Region 
 
 Number of 
 samples 
 
 Decree 
 Balling 
 
 Number 
 
 of samples 
 
 scoring 
 
 mature 
 
 Per cent 
 
 of samples 
 
 scoring 
 
 mature 
 
 
 • 
 
 63 
 47 
 69 
 
 8 
 7 
 14 
 
 30 
 52 
 23 
 
 17 
 18 
 19 
 
 17 
 18 
 19 
 
 17 
 18 
 19 
 
 49 
 40 
 65 
 
 3 
 4 
 
 12 
 
 3 
 21 
 13 
 
 78 
 85 
 
 
 94 
 
 38 
 57 
 
 
 f 
 
 86 
 
 10 
 40 
 
 
 57 
 
 THE INFLUENCE OF SEASONAL TEMPERATURES ON THE 
 COMPOSITION AND PALATABILITY OF GRAPES 
 
 The dates of ripening and of the development of color vary with 
 the season. The most general and perhaps the principal factor of 
 the cause of this is the mean of the daily maximum air temperature 
 during the development and ripening of the fruit. Fortunately, for 
 the purpose of the investigation, there was an unusually large varia- 
 tion in this factor during the three seasons covered and one of them 
 diverged widely from the mean of the localities considered. 
 
 The season of 1931 was peculiar in that for the early sections the 
 mean daily maximum temperature was considerably below normal, 
 while in the later sections the mean daily maximum temperature was 
 well above normal. In the Coachella Valley there was also a sufficient 
 difference in the temperature before and during harvesting between 
 the season of 1929 and that of 1930 to be reflected in the fruit. 
 
Bul, 529] 
 
 Maturity Tests for Table Grapes 
 
 17 
 
 The Coachella Valley. — This valley is the earliest commercial 
 grape -growing 1 section in California. Here the fruit develops very 
 rapidly, i.e. the period of time required for the growth and maturing 
 of the fruit is relatively short. In view of the rapid development 
 of the fruit, the temperature records for this section were compiled 
 for a period of thirty days before the date of harvesting. A period 
 of such length was sufficient to cover the ripening period and hence 
 to embrace the chief effects of temperature on the composition and 
 palatability of the fruit at harvesting. 
 
 The influence of the seasonal temperatures of the Coachella 
 Valley on the degree Balling of grapes of the same per cent acidity is 
 shown in table 6. The influence of the same conditions on the per 
 cent acidity and the eating quality of the fruit at the same degree 
 Balling is shown in table 7. 
 
 TABLE 6 
 
 The Influence of Seasonal Temperature on the Degree Balling of Grapes 
 
 of the Same Acid Content: Coachella Valley 
 
 
 Year 
 
 Mean maximum 
 temperature 
 for 30 days 
 
 before 
 harvesting, 
 
 degrees 
 Fahrenheit 
 
 Per cent acid 
 
 Variety 
 
 0.55 to 
 0.60 
 
 0.60 to 
 0.65 
 
 0.65 to 
 70 
 
 0.70 to 1 0.75 to 
 075 80 
 
 0.80 to 
 0.85 
 
 0.85 to 
 0.90 
 
 
 Degree Balling 
 
 Thompson { 
 
 1929 
 
 1092 
 
 18 5 
 
 18 .6 
 
 18.7 
 
 18 1 
 
 18 2 
 
 
 
 Seedless -j 
 
 1930 
 
 105.6 
 
 19 3 
 
 19 4 
 
 19 4 
 
 19 2 
 
 19 
 
 
 
 1931 
 
 97.9 
 
 
 
 
 20 3 
 
 20 .6 
 
 20.2 
 
 20 1 
 
 ( 
 
 1929 
 
 109 .2 
 
 18 6 
 
 17.8 
 
 18 3 
 
 18 5 
 
 18 3 
 
 
 
 Malaga \ 
 
 1930 
 
 105.6 
 
 18.5 
 
 18.7 
 
 18 9 
 
 18 4 
 
 18.9 
 
 
 
 I 
 
 1931 
 
 97.9 
 
 
 19.9 
 
 19.9 
 
 19 5 
 
 19.2 
 
 19 1 
 
 18.7 
 
 As was indicated in the discussion of the influence of regional 
 conditions in connection with table 2, the figures of table 6 show 
 no significant difference in the degree Balling at the various per cents 
 of acidity over the range of acidity of the samples. There is, however, 
 a definite indication of the influence of seasonal temperatures on the 
 degree Balling of the samples of fruit of the same acidity. In 1929 
 the average Balling reading of the Thompson Seedless fruit over the 
 entire range of acidity was 0.8° lower than in 1930 and 1.9° lower 
 than in 1931. For the Malaga the Balling reading of the 1929 fruit 
 was 0.4° lower than that of 1930 and 1.2° lower than that of 1931. 
 These differences in degree Balling are directly correlated with the 
 seasonal conditions of temperature. In 1929 the mean maximum 
 
18 
 
 University of California — Experiment Station 
 
 temperature for the thirty-day period before harvesting: was 3.6° F 
 higher than in 1930 and 11.3° F higher than in 1931. Similarly, the 
 difference in the degree Balling was less between 1929 and 1930 than 
 between 1930 and 1931. 
 
 TABLE 7 
 
 The Influence of Seasonal Conditions on the Acidity and the Palatability 
 
 of Grapes of the Same Degree Balling 
 
 
 Years 
 
 Mean 
 
 maximum 
 
 temperature 
 
 30 days 
 
 before 
 
 harvesting, 
 
 degrees 
 Fahrenheit 
 
 Degree Balling of expressed juice 
 
 Scoring of 
 samples of 17° to 19° 
 
 
 17.0 to 
 17.9 
 
 18.0 to 
 18.9 
 
 19.0 to 
 19.9 
 
 Balling 
 
 Variety 
 
 Per cent 
 scored 
 mature* 
 
 Per cent 
 
 
 Per cent acid 
 
 scored 
 poor 
 
 Thompson f 
 
 1929 
 
 109.2 
 
 69 
 
 66 
 
 66 
 
 85 
 
 15 
 
 Seedless... \ 
 
 1930 
 
 105.6 
 
 79 
 
 77 
 
 76 
 
 45 
 
 55 
 
 i 
 
 1931 
 
 97.9 
 
 1.02 
 
 1 04 
 
 1 04 
 
 11 
 
 89 
 
 f 
 
 1929 
 
 109.2 
 
 66 
 
 0.62 
 
 56 
 
 78 
 
 22 
 
 Malaga \ 
 
 1930 
 
 105.6 
 
 0.71 
 
 67 
 
 62 
 
 65 
 
 35 
 
 { 
 
 1931 
 
 97.9 
 
 0.86 
 
 0.77 
 
 74 
 
 28 
 
 72 
 
 * Mature as used here refers to all of the samples scoring fair or better. 
 
 The figures of table 7 show that with a drop from 109.2° to 105.6° 
 F in the mean daily temperature for thirty days before harvesting, 
 there was a marked increase in the acidity. In the Thompson Seedless 
 this increase was 14.5 per cent at 17° Balling, 16 per cent at 18° Ball- 
 ing, and 15.2 per cent at 19° Balling in 1930 as compared to that 
 of 1929. With a further reduction in the mean temperature during 
 the thirty-day period before harvesting from 105.6° F in 1930 to 
 97.9° F in 1931 there was an increase in the acidity of 29 per cent 
 at 17° Balling, 35 per cent at 18° Balling, and 35 per cent at 19° 
 Balling. The increases in the acidity of the Malaga at the same 
 degree Balling with the drops in the mean maximum temperatures as 
 indicated above were proportional to those of Thompson Seedless but 
 of only about one-half the magnitude. 
 
 The influence of the seasonal conditions in the Coachella Valley 
 on palatability is shown in the two columns at the right of table 7. 
 For the Thompson Seedless samples 17°, 18°, and 19° Balling 85 
 per cent were considered good to eat in 1929, 45 per cent in 1930, and 
 11 per cent in 1931. For the Malaga samples of these same degrees 
 Balling 78 per cent were scored as mature in 1929, 65 per cent in 
 1930, and 28 per cent in 1931. The palatability of the samples reflects 
 the relative influence of the seasonal conditions on the relation of the 
 degree Balling to the per cent acidity. This relation was influenced 
 
Bul. 529] 
 
 Maturity Tests for Table Grapes 
 
 19 
 
 more by the seasonal conditions in the Thompson Seedless than in 
 the Malaga. Likewise the Thompson Seedless samples show a greater 
 spread in palatability for the three years than those of the Malaga. 
 
 Kern County and Fresno County. — The influence of the tempera- 
 ture conditions of those two regions will be presented together. Here 
 the period required for the maturing of the fruit is longer than in the 
 Coachella Valley. It is also somewhat longer in Fresno than in Kern 
 County. With the lengthening of the season required for the develop- 
 ment of the fruit the period of time before harvesting for which the 
 temperature records were compiled was increased to 40 days. 
 
 The influence of the seasonal temperatures of these sections on 
 the degree Balling of grapes of the same per cent acidity is shown in 
 table 8 and the influence on the per cent acidity and palatability is 
 shown in table 9. 
 
 TABLE 8 
 
 The Influence of Seasonal Temperature on the Degree Balling of Grapes 
 
 of the Same Acid Content 
 
 
 
 Mean 
 
 
 
 Per cent acid 
 
 
 
 
 Year 
 
 maximum 
 temperature 
 for 40 days 
 
 before 
 harvesting, 
 
 degrees 
 Fahrenheit 
 
 
 
 
 
 
 Variety 
 
 0.60 to 
 0.65 
 
 0.65 to 
 0.70 
 
 0.70 to 
 0.75 
 
 0.75 to 
 0.80 
 
 0.80 to 
 0.85 
 
 0.85 to 
 90 
 
 
 Degree Balling 
 
 Thompson 
 
 1929 
 
 101 6 
 
 20 1 
 
 20 2 
 
 19.6 
 
 19.4 
 
 19 2 
 
 
 Seedless \ 
 
 1930 
 
 101.8 
 
 19.2 
 
 19.4 
 
 19.2 
 
 19 
 
 19.5 
 
 
 (Kern County) { 
 
 1931 
 
 96 3 
 
 
 
 21.0 
 
 21.9 
 
 21.8 
 
 21.1 
 
 ( 
 
 1929 
 
 93.5 ) 
 
 
 21.6 
 
 21.3 
 
 21.4 
 
 20.7 
 
 20 4 
 
 Malaga j 
 
 1930* 
 
 92.5/ 
 
 
 
 
 
 
 
 (Fresno County) ( 
 
 1931 
 
 103.2 
 
 19 1 
 
 18.5 
 
 18.5 
 
 18.7 
 
 18 1 
 
 
 * Only 24 samples of Malaga were collected in Fresno County in 1930. Owing to the similarity in 
 the temperature of this season with that of 1929, as indicated in table 8, these samples are combined with 
 those of 1929. 
 
 In these regions the mean maximum temperature for the forty-day 
 period before harvesting in 1929 and 1930 was almost the same. The 
 degree Balling of the fruit for these seasons at the same per cent 
 acidity also was almost the same. For Kern County in 1931 when 
 the mean maximum temperature for the period before harvesting 
 was 5.5° F lower than in 1929 and 1930, the Balling for the fruit of 
 the same per cent acidity was 1.9° Balling higher. 
 
 The data of table 8 show a reversal of temperature conditions in 
 Fresno County as compared to Kern County and the Coachella Valley 
 sections. Here the mean maximum temperature for the forty-day 
 period before harvesting was higher in 1931 than in 1929 and 1930. 
 
20 
 
 University of California — Experiment Station 
 
 The increase of 10.2° F in the temperature of 1931 over the average 
 for the same period of time in 1929 and 1930 was accompanied by a 
 reduction of 2.5° Balling of the fruit of the same per cent acidity 
 in this season. 
 
 TABLE 9 
 
 The Influence of Seasonal Conditions on the Acidity and the Palatability 
 
 of Grapes of the Same Degree Balling 
 
 
 Year 
 
 Mean 
 
 maximum 
 
 temperature 
 
 for 40 days 
 
 before 
 harvesting, 
 
 degrees 
 Fahrenheit 
 
 Degree Balling of expressed juice 
 
 Scori 
 samples 
 
 ngof 
 17° to 19° 
 
 
 17.0 to 
 17.9 
 
 18.0 to 
 18.9 
 
 19.0 to 
 19.9 
 
 Balling 
 
 Variety 
 
 Per cent 
 scored 
 mature 
 
 Per cent 
 
 
 Per cent acid 
 
 scored 
 poor 
 
 Thompson ( 
 
 1929 
 
 101 6 
 
 0.78 
 
 0.76 
 
 69 
 
 46 
 
 54 
 
 Seedless .-{ 
 
 1930 
 
 1018 
 
 80 
 
 77 
 
 70 
 
 42 
 
 58 
 
 (Kern Co.) [ 
 
 1931 
 
 96.3 
 
 1.08 
 
 1.09 
 
 1.05 
 
 14 
 
 86 
 
 Malaga f 
 
 1929 
 
 93.5) 
 
 78 
 
 75 
 
 70 
 
 38 
 
 62 
 
 (Fresno i 
 
 1930 
 
 92.5/ 
 
 
 
 
 
 
 County) [ 
 
 1931 
 
 103.2 
 
 68 
 
 0.64 
 
 0.59 
 
 71 
 
 29 
 
 The figures of table 9 indicate that under conditions of about the 
 same temperature the acidity of the grapes of the same degree Balling 
 was about the same. There was no significant difference in the acidity 
 of the Thompson Seedless in Kern County in 1929 and 1930. The 
 same was true for the Malaga in Fresno in these seasons. With a drop 
 in 1931 of 5.5° F in Kern County in the mean maximum temperature 
 for the period before harvesting the acidity of Thompson Seedless 
 was 35 per cent higher at 17° Balling, 41 per cent higher at 18° 
 Balling, and 50 per cent higher at 19° Balling than in 1929 and 1930. 
 In the Fresno section, on the contrary, where the temperature for 
 1931 was 10.2° F higher than in 1929 and 1930 there was a reduction 
 of the acidity in this season of 13 per cent at 17° Balling, 15 per cent 
 at 18° Balling, and 16 per cent at 19° Balling. 
 
 During 1929 and 1930, when the seasonal influences on the fruit 
 of the Kern section were about the same, approximately the same 
 amount of fruit at 17°, 18°, and 19° Balling was considered mature by 
 the scorers. The great increase in the acidity of the fruit of these 
 degrees Balling in this section in 1931 caused the scorers to mark only 
 14 per cent of it mature. 
 
 Of the fruit of 17°, 18°, and 19° Balling collected in the Fresno 
 section in 1929 and 1930 the scorers marked 38 per cent mature. The 
 considerable reduction in the acidity of the fruit in 1931 resulted in 
 the scoring of 71 per cent of the fruit of this season as mature. 
 
Bul, 529 
 
 Maturity Tests for Table Grapes 
 
 21 
 
 THE RELATION OF ACIDITY AND DEGREE BALLING TO 
 PALATABILITY 
 
 In the preceding parts of this paper the influence of regional and 
 seasonal conditions on the acidity and the sugar content of the 
 expressed juice of grapes was discussed. The relation of these sub- 
 stances to the eating quality of the grape will now be considered. 
 For this purpose three varieties will be selected : one to represent the 
 
 TABLE 10 
 The Belation of Per Cent Acid and Degree Balling to the Palatability of 
 
 Grapes 
 
 Degree Balling 
 
 Molinera (Red Malaga) 
 
 16 to 16. 9 
 
 17.0 to 17. 9 
 
 18 Oto 18.9 
 
 19 to 19. 9 
 
 20 Oto 20. 9 
 
 21. Oto 21. 9 
 
 Emperor 
 
 17.0 to 17. 9 
 
 18 Oto 18. 9 
 
 19 Oto 19.9 
 
 20. Oto 20. 9 
 
 21.0 to 22.9 
 
 23 
 
 Thompson Seedless 
 
 17.0 to 17.9 
 
 18.0 to 18. 9 
 
 19. Oto 19. 9 
 
 20. Oto 21. 9 
 
 22.0 to 23 9 
 
 24 or more 
 
 Per cent acid 
 
 35 
 
 to 
 
 0.40 
 
 40 
 
 to 
 
 0.45 
 
 45 
 
 to 
 
 0.50 
 
 50 
 
 to 
 
 55 
 
 55 
 
 to 
 
 0.60 
 
 60 
 
 to 
 
 65 
 
 65 
 
 to 
 
 70 
 
 70 
 
 to 
 75 
 
 75 
 
 to 
 
 80 
 
 80 
 
 to 
 
 0.85 
 
 0.85 
 
 to 
 
 90 
 
 Palatability scores* 
 
 22.5 
 
 22.5 
 
 20 
 
 15 
 
 17 5 
 
 15 
 
 7.5 
 
 
 
 
 27.5 
 
 25.0 
 
 22 5 
 
 22.5 
 
 20 
 
 17.5 
 
 12.5 
 
 
 
 
 22.5 
 
 25.0 
 
 32 5 
 
 25.0 
 
 22.5 
 
 22.5 
 
 20.0 
 
 
 
 
 40.0 
 
 40.0 
 
 40 
 
 42.5 
 
 35 
 
 37.5 
 
 35 
 
 
 
 
 42.5 
 
 47.5 
 
 45.0 
 
 40 
 
 47.5 
 
 40 
 
 40 
 
 
 
 
 
 57.5 
 
 62.5 
 
 62 5 
 
 52 5 
 
 52.5 
 
 60 
 
 
 
 
 
 
 20.0 
 
 25 
 
 22 5 
 
 20 
 
 17.5 
 
 22.5 
 
 15 
 
 
 
 
 25 
 
 22 5 
 
 22.5 
 
 30 
 
 30 
 
 25 
 
 20 
 
 
 
 
 27.5 
 
 30 
 
 35 
 
 32.5 
 
 32.5 
 
 30 
 
 22.5 
 
 
 
 
 37 5 
 
 37.5 
 
 35 
 
 37 5 
 
 35 
 
 35 
 
 25.0 
 
 
 
 
 45 
 
 42 5 
 
 37.5 
 
 45.0 
 
 45 
 
 42 5 
 
 37.5 
 
 
 
 
 52 5 
 
 45 
 
 50 
 
 47.5 
 
 55 
 
 42.5 
 
 37 5 
 
 
 
 
 
 
 25 
 
 30 
 
 32.5 
 
 25.0 
 
 25 
 
 20 
 
 
 
 
 
 30 
 
 32.5 
 
 32.5 
 
 35.0 
 
 27.5 
 
 25 
 
 
 
 
 
 32 5 
 
 37.5 
 
 37.5 
 
 32 5 
 
 30 
 
 27.5 
 
 
 
 
 
 42 5 
 
 42.5 
 
 42 5 
 
 45 
 
 37.5 
 
 37 5 
 
 
 
 
 
 50 
 
 50 
 
 50 
 
 52.5 
 
 50 
 
 42 5 
 
 
 
 
 
 62.5 
 
 62.5 
 
 62.5 
 
 67.5 
 
 65.0 
 
 52.5 
 
 15.0 
 17 5 
 17.5 
 30.0 
 37.5 
 47.5 
 
 * A palatability score of 25 or more indicates that the fruit was fair or better in eating quality. 
 
 group of varieties of low acidity, another to represent those of medium 
 acidity, and a third to represent those of high acidity. To show 
 the relation of each of these substances to palatability, the average 
 scores of the tasters for the samples at each degree Balling, and at 
 the various per cents of acid over the entire range of acidity for the 
 varieties, are included in table 10. The scores at each degree Balling, 
 
22 University of California — Experiment Station 
 
 i.e. the figures across the table, show the influence of acidity on eating 
 quality. The figures at a given per cent of acidity, i.e., the scores 
 shown in the various columns of the table, indicate the relation of 
 degree Balling to palatability. 
 
 The figures of table 10 indicate a relation between acidity and 
 palatability. In each variety the palatability scores are reduced as 
 the acidity becomes somewhat high. This reduction was most pro- 
 nounced in the samples of low Balling. Yet with the highest degree 
 Balling shown there was a slight reduction in the palatability score 
 of the samples of each variety, except those of Molinera, at the higher 
 acidities. This relation of acidity to eating quality for the three 
 varieties is possibly more clearly illustrated by the graphs of figure 2. 
 The significance of the relation of acidity to eating quality is shown 
 by the correlation computation of table 11. 
 
 ^3S 
 ^ 30 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 , / 
 
 r/)ompso/7 Seed/e* 
 
 $s 
 
 
 
 Vfo/mera 
 
 
 
 
 »»*°""" 
 
 J&- 
 
 o.^ 
 
 . 
 
 
 
 / 
 
 3=^-^ 
 
 
 
 
 t/fmpt 
 
 >ror 
 
 % "*V» 
 
 ■» v 
 
 
 
 
 
 ^ 
 
 -»— _*>" 
 
 
 
 \ 
 
 
 x 
 
 N 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 \> 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 o.js 040 o.4s oso ass oao oas O70 O 7S OSO OSS O-ffO 
 
 Per Ceo f dad/ ft/ of f/?e Gropes. 
 
 Fig. 2. — The relation of aeidity to eating quality. 
 
 The relation of degree Balling to palatability, as shown by the 
 figures of table 10, is much more definite than that shown for the 
 acidity. An increase in the degree Balling was accompanied by a 
 decided increase in palatability at each of the different per cents of 
 acidity. The increase in score between the lowest and the highest 
 degree Balling for each of the varieties at a given acidity was 100 
 per cent or more. This relation of degree Balling to eating quality 
 is more clearly indicated by the graphs of figure 3. Its significance 
 is further confirmed by the data of table 11. 
 
Bul. 529] 
 
 Maturity Tests for Table Grapes 
 
 23 
 
 55 
 
 50 
 
 45 
 
 S 40 
 
 
 ?5 
 
 SO 
 
 /5 
 
 /O 
 
 
 
 
 
 
 
 
 
 -■ 
 
 "* 
 
 
 
 
 Mo/ 
 
 '/?era-?^~ 
 
 1 T/?o/7?pso/7 Seed/ess — ^. 
 
 
 
 
 
 
 
 
 
 ,-■'■"" ^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 r 
 
 , 1 ' ' 
 ,*' t s -~&~> fmperor 
 
 
 
 
 
 
 
 v 
 
 
 
 
 
 
 
 
 
 ''"°p 
 
 
 
 
 
 
 
 
 
 V 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 // /<? /i> <?<? iV -A? /?J- <?-* AT ^ 
 
 degrees 8a////?g 
 Fig. 3. — The relation of degree Balling to eating quality. 
 
 TABLE 11 
 The Correlation of Acidity and Degree Balling with Palatability 
 
 
 Years 
 included 
 
 Correlations 
 
 Variety 
 
 Balling with 
 palatability 
 
 Acidity with 
 palatability 
 
 
 1927-1930 
 1927-1930 
 1927-1930 
 1927-1930 
 1927-1930 
 1927-1930 
 1927-1930 
 1929 
 
 -f0 735-4-11 nu. 
 
 523±0 019 
 
 
 +0 
 +0 
 +0 
 +0 
 +0 
 +0 
 +0 
 
 649±0.017 
 635±0 020 
 681±0 018 
 656±0 021 • 
 546±0.035 
 815±0 014 
 715±0 049 
 
 640±0 018 
 
 Tokay 
 
 Emperor 
 
 Rjbier 
 
 Muscat 
 
 -0.368±0 030 
 -0 144±0 034 
 -0 420±0 031 
 —0 367zb0 044 
 
 Molinera (Red Malaga) 
 
 +0 009±0 041 
 — 480±0 057 
 
 Ohanez 
 
 
 
 
 
 The figures of table 11 indicate that the correlation of acidity 
 and palatability is of questionable significance when applied to all 
 of the varieties. In the Thompson Seedless and Malaga the average 
 correlation for the four seasons is sufficiently high to be decidedly 
 significant. In single seasons and for given localities, however, the 
 correlations for these varieties dropped in some instances as low as 
 — 0.30 ±0.12 and — 0.35 ± 0.10, respectively. These correlations 
 are of doubtful significance. In the Tokay, Ribier, Muscat, and 
 Ohanez the correlation figures are near the lower limits of being con- 
 
24 University of California — Experiment Station 
 
 sidered significant. The figures for the Emperor and Molinera fail to 
 show any significant correlation of acidity with eating quality. 
 
 The correlations of degree Balling and palatability are all very 
 high. The influence of seasonal and regional conditions upon these 
 correlations have not been as clearly indicated as for the correlations 
 of acidity and palatability. 
 
 ACIDITY AS A MEANS OF MEASURING MATURITY 
 
 Many of the poor table grapes that get on the markets are poor 
 because they are green, i.e., not ripe enough for dessert purposes. 
 This fruit is immature because its acidity is too high in relation to its 
 sugar content. To overcome this condition it has frequently been 
 suggested that acidity rather than degree Balling be used as a basis 
 for measuring maturity. 
 
 That the acidity of the grape is not a suitable constituent for the 
 purposes of standardization is shown in tables 10 and 11 and figure 2. 
 It bears a certain relation to palatability but its influence per se on 
 palatability is not sufficiently marked. For the three varieties used 
 the difference in the palatability score was only 17 per cent in the 
 acidity range 0.38 to 0.63 per cent, for Molinera; 7 per cent in the 
 acidity range 0.48 to 0.73 per cent, for Emperor; and 9 per cent in 
 the acidity range 0.58 to 0.78 per cent, for Thompson Seedless. When 
 it is considered that these ranges in acidity include the majority of 
 the grapes of these varieties that appear on the markets, it is obvious 
 that the difference in eating quality at the different percentages of 
 acid is not sufficient to make it possible to separate the good from 
 the poor grapes on the basis of acidity. The slopes of the graphs in 
 figure 2 also show this indefiniteness of the relation of acidity and 
 palatability. Except for the point of highest acidity in the Emperor 
 and the two points of highest acidity in the Thompson Seedless, the 
 graphs are relatively straight. 
 
 Further evidence against the use of acidity as a basis of measuring 
 maturity is offered by the correlation calculations shown in table 11. 
 Here the correlation of acidity with palatability is shown to range 
 from — 0.640 ± 0,018 in the Malaga down to — 0.144 ± 0.034 in the 
 Emperor and on down to -f- 0.009 ± 0.041 in the Molinera. In other 
 words, there is no consistently significant correlation between acidity 
 and eating quality when all of the varieties are considered. Even the 
 relatively high average correlations shown for the Malaga and Thomp- 
 son Seedless, lose their apparent importance when the correlations 
 
Bul, 529] Maturity Tests for Table Grapes 25 
 
 for these varieties in the various localities in which they are grown 
 are considered individually. To be of value as a measure of maturity 
 the relation of acidity to palatability would of necessity have to be 
 fairly constant for all of the varieties and especially so for the 
 individual varieties. 
 
 DEGREE BALLING AS A MEANS OF MEASURING MATURITY 
 
 The degree Balling of the expressed juice of grapes has been used 
 for many years in California as a means of measuring maturity. Its 
 use in this connection was given legal recognition in the Standardiza- 
 tion law of 1915. Although no single composition test has been found 
 sufficiently accurate as a measure of the maturity of grapes in this 
 investigation, degree Balling has a higher degree of correlation with 
 eating quality than any other. This high degree of correlation is 
 indicated by the figures of tables 10 and 11. 
 
 Despite its long use as a means of determining maturity and the 
 above data which appear to indicate that degree Balling should serve 
 well for this purpose, its use in the standardization of table grapes 
 has not been entirely satisfactory. In some seasons it has worked 
 well, while in others a relatively large quantity of fruit that met 
 the Balling requirement, but which was nevertheless poor in eating 
 quality, was placed on the markets. The nature of the limitations 
 of degree Balling can be shown by indicating how it has functioned 
 as a means of separating the good and poor samples of fruit used 
 in these tests. First, figures will be presented to show the actual 
 results obtained with the degree Balling requirement as set forth 
 in the Standardization law of 1931. After this, the possibility of 
 improving the functioning of this means of determining palatability 
 by raising the degree Balling requirement will be indicated. 
 
 The 1931 Standardization Law. — The degree of satisfaction with 
 which the present Balling requirement is functioning may be indi- 
 cated by showing the percentage of poor fruit that it permits to reach 
 the markets. To do this, the samples of fruit used in this investiga- 
 tion that were of a Balling reading equal to or above the present 
 legal requirement were divided into two groups. One group was 
 made up of the samples that were considered poor in eating quality 
 by the scorers, and the other was made up of all the samples that were 
 considered fair or better in eating quality. The results of this 
 grouping of the samples on the basis of palatability is shown in 
 table 12. The good fruit excluded by this requirement is also shown. 
 
26 
 
 University of California — Experiment Station 
 
 These figures indicate that of the fruit meeting the 1931 standard- 
 ization requirements as regards degree Balling 10 to 26 per cent was 
 considered to be poor in eating quality. On this basis an average of 
 20.0 per cent of the fruit of the eleven varieties that met this require- 
 ment was scored as not being good to eat. This is indeed a very high 
 percentage. If the samples of fruit were representative of the fruit 
 that moved to market, and there is every reason to believe that they 
 were, the 1931 degree Balling requirement is not sufficiently effective 
 as a means of keeping the poor grapes off our markets. 
 
 TABLE 12 
 
 The Present Degree Balling Requirement as a Means of Measuring 
 
 Maturity in Relation to Palatability 
 
 Variety 
 
 The 1931 
 standardiza- 
 tion 
 requirement* 
 
 Number 
 of samples 
 equal to or 
 above the 
 1931 degree 
 
 Balling 
 requirement 
 
 Fruit 
 
 scoring fair 
 
 or better 
 
 Fruit 
 
 scoring 
 
 poor 
 
 Fruit scoring 
 
 fair or better 
 
 excluded by 
 
 the 1931 
 
 degree 
 
 Balling 
 
 requirement 
 
 Thompson Seedless 
 
 degrees Balling 
 17 
 17 
 17 
 17 
 17 
 18 
 16 
 16 
 16 
 16 
 16 
 
 709 
 
 648 
 
 469 
 
 104 
 
 59 
 
 200 
 
 438 
 
 242 
 
 226 
 
 65 
 
 45 
 
 per cent 
 
 74 
 83 
 78 
 81 
 84 
 90 
 76 
 85 
 84 
 88 
 80 
 
 per cent 
 26 
 17 
 22 
 19 
 14 
 10 
 24 
 15 
 16 
 12 
 20 
 
 per cent 
 
 
 
 0.8 
 
 Tokay 
 
 8 
 
 Ohanez 
 
 
 
 
 4 
 
 
 15 
 
 
 0.0 
 
 
 3 6 
 
 
 4 
 
 
 0.0 
 
 
 
 
 
 
 * The California Fruit, Nut, and Vegetable Standardization Act of 1931. 
 
 Higher Degree Balling Requirements. — A raise in the degree Ball- 
 ing requirement has been advocated by many individuals as a solution 
 to the limitations of the present and past Balling requirements. The 
 probable success of such a revision is indicated by the figures of tables 
 13 and 14. The figures of these tables are similar to those of table 12 
 except that in table 13 the minimum is one degree Balling and in 
 table 14 two degrees Balling above the 1931 requirement. The per- 
 centage of good fruit eliminated by these increases in degree Balling 
 is shown in the column at the right of the tables. 
 
 The figures of table 13 show that an increase of 1° Balling in the 
 minimum requirement has excluded 30 per cent of the poor fruit that 
 was equal to or above the 1931 Balling requirement. The increase of 
 1° Balling has also excluded an average of 4.8 per cent of the fruit 
 that scored fair or better. 
 
Bul. 529] 
 
 Maturity Tests for Table Grapes 
 
 27 
 
 TABLE 13 
 
 A Degree Balling Kequirement of 1° Higher Than That of 1931 as a Means 
 
 of Measuring Maturity in Belation to Palatability 
 
 Variety 
 
 Degrees 
 Balling 
 
 Fruit 
 scoring 
 fair or 
 better 
 
 Fruit 
 
 scoring 
 
 poor 
 
 Fruit 
 scoring fair 
 
 or better 
 
 excluded by 
 
 the increase of 
 
 1° Balling 
 
 Thompson Seedless 
 
 18 
 18 
 18 
 18 
 18 
 19 
 17 
 17 
 17 
 17 
 17 
 
 per cen t 
 90 
 92 
 84 
 88 
 88 
 92 
 79 
 95 
 92 
 100 
 85 
 
 per cent 
 10 
 
 8 
 
 16 
 12 
 12 
 
 8 
 21 
 
 5 
 
 8 
 
 
 36 
 
 per cent 
 6 
 
 
 9 
 
 Tokay 
 
 Ohanez 
 
 1 
 
 
 
 34 
 
 
 3 
 
 Emperor 
 
 
 13 
 
 
 1 
 
 
 5 
 
 
 
 
 
 
 TABLE 14 
 
 A Degree Balling Kequirement of 2° Higher Than That of 1931 as a Means 
 
 of Measuring Maturity in Belation to Palatability 
 
 Variety 
 
 Degrees 
 Balling 
 
 Fruit 
 scoring 
 fair or 
 better 
 
 Fruit 
 
 scoring 
 
 poor 
 
 Fruit 
 scoring fair 
 
 or better 
 
 excluded by 
 
 the increase of 
 
 2° Balling 
 
 Thompson Seedless 
 
 19 
 19 
 19 
 19 
 19 
 20 
 18 
 18 
 18 
 18 
 18 
 
 per cent 
 
 95 
 
 97 
 
 91 
 
 92 
 100 
 100 
 
 85 
 
 99 
 
 99 
 100 
 
 93 
 
 per cent 
 5 
 3 
 9 
 8 
 
 
 15 
 1 
 1 
 
 7 
 
 per cent 
 15 
 
 
 21 
 
 Tokay 
 
 4 
 
 
 8 
 
 
 64 
 
 
 6 
 
 
 2 
 
 
 26 
 
 
 8 
 
 Rish Baba 
 
 16 
 
 
 7 
 
 
 
 By raising the minimum 2° Balling above the 1931 requirement, 
 as shown in table 14, 75 per cent of poor fruit was excluded. This 
 increase of 2° Balling, although quite effective in reducing the per- 
 centage of poor fruit that was admitted by the 1931 requirement, 
 increased the amount of good fruit that was excluded to 12 per cent. 
 
 These figures clearly illustrate the insufficiency of degree Balling 
 as a means of measuring maturity. It is true that a sufficiently high 
 degree Balling will exclude practically all of the poor fruit. To 
 
28 University of California — Experiment Station 
 
 increase the requirement to that extent, however, is too costly in 
 delaying' the harvesting- of the considerable quantity of fruit that is 
 good to eat before it reaches this higher standard. In the warmer 
 regions such a delay in harvesting-, especially in the hotter seasons, 
 would result in the loss of much of the fruit that becomes good to 
 eat at 17° and 18° Balling. 
 
 The Defects of Degree Balling as a Means of Measuring Matur- 
 ity. — In view of the very high degree of correlation between degree 
 Balling and palatability shown in tables 10 and 11 and figure 3, and 
 the insufficiency of degree Balling' as a means of measuring palata- 
 bility as shown in tables 12, 13, and 14, it would appear that some- 
 thing- has been missed in the endeavor to find the actual relation of 
 degree Balling to palatability. The factor which would most likely 
 clear up this apparent discrepancy is the influence of regional and 
 seasonal conditions on the correlation of degree Balling and 
 palatability. 
 
 In collecting the samples of fruit for this investigation they were 
 all tasted so as to have them fall within a given range of palatability. 
 This procedure tended to mask the effects of regional and seasonal 
 conditions by bringing about a shift in the degree Balling of the fruit 
 collected in different regions and seasons. When the conditions were 
 such that the fruit became palatable at a, low degree Balling, more 
 fruit toward the lower end of the Balling range was collected. On 
 the contrary, when the conditions were such that the fruit of the 
 lower degrees Balling was unpalatable, the majority of the samples 
 were collected in the middle or at the higher part of the degree Ball- 
 ing range. Since all of the fruit was within the same relatively 
 narrow range of palatability it is not surprising that the correlation 
 between its degree Balling and palatability is about the same in the 
 different regions and seasons. 
 
 Although the data collected do not clearly show the influence of 
 seasonal and regional conditions on the correlation of degree Balling 
 and palatability when the entire Balling range over which fruit was 
 collected is used, the importance of the influence of these conditions 
 can be indicated by using only the fruit of 17°, 18°, and 19° Balling. 
 The influence of regional conditions on palatability at these degrees 
 Balling as indicated by the scores of the tasters is shown in table 15. 
 The influence of seasonal conditions on the palatability score of fruit 
 of the same degrees Balling is indicated in table 16. 
 
 The figures of table 15 indicate that the palatability score of the 
 Thompson Seedless fruit of the Coachella and Imperial valleys was 17 
 
Bul. 529] 
 
 Maturity Tests for Table Grapes 
 
 29 
 
 per cent higher at 17° Balling, 40 per cent higher at 18° Balling, and 
 36 per cent higher at 19° Balling than that of Kern County. The 
 score of the fruit of this variety was 47 per cent at 17° Balling, 53 
 per cent at 18° Balling, and 44 per cent at 19° Balling higher in 
 Coachella and Imperial valleys than in the region Fresno-to-Davis. 
 Differences of about the same magnitude are shown by the scores for 
 the Malaga fruit of these regions. 
 
 TABLE 15 
 
 The Influence of Kegional Condition on the Palatability Score of Grapes 
 
 of 17° to 19° Balling, for 1929 
 
 
 Region 
 
 Palatability scores 
 
 Variety 
 
 At 17.0° to 
 17.9° Balling 
 
 At 18.0° to 
 18.9° Balling 
 
 At 19.0° to 
 19.9° Balling 
 
 Thompson Seed- f 
 
 
 30 
 25 
 16 
 
 34 
 24 
 12 
 
 45 
 27 
 21 
 
 37 
 31 
 15 
 
 48 
 
 less .-j 
 
 
 31 
 
 
 
 27 
 
 r 
 
 
 39 
 
 
 
 29 
 
 1 
 
 
 22 
 
 
 
 
 TABLE 16 
 
 The Influence of Seasonal Conditions on the Palatability Score of 
 
 Grapes of 17° to 19° Balling 
 
 
 
 
 
 Year 
 
 Mean 
 
 maximum 
 
 temperature 
 
 before 
 harvesting,* 
 
 degrees 
 Fahrenheit 
 
 Palatability scores 
 
 Variety 
 
 Region 
 
 At 17.0° 
 to 17.9° 
 Balling 
 
 At 18.0° 
 to 18.9° 
 Balling 
 
 At 19.0° 
 to 19.9° 
 Balling 
 
 f 
 
 
 f 
 
 1929 
 1930 
 1931 
 
 1929 
 1930 
 1931 
 
 1929 
 1930 
 1931 
 
 1929 
 1930 
 1931 
 
 109.2 
 105.6 
 
 97.9 
 
 101.6 
 
 101 8 
 
 96.3 
 
 109.2 
 105.6 
 
 97.9 
 
 93.5) 
 92.5/ 
 103.2 
 
 31 
 20 
 12 
 
 26 
 27 
 17 
 
 33 
 
 22 
 19 
 
 12 
 
 26 
 
 44 
 26 
 13 
 
 27 
 26 
 21 
 
 38 
 26 
 24 
 
 15 
 
 30 
 
 46 
 37 
 
 Thompson 
 Seedless • 
 
 
 
 1 
 
 19 
 
 30 
 31 
 
 
 Coachella Valley < 
 
 25 
 
 39 
 31 
 
 
 
 26 
 
 
 Fresno County • 
 
 ' 
 
 22 
 33 
 
 * For a 30-day period in Coachella Valley and a 40-day period in Kern and Fresno counties. 
 
30 University of California — Experiment Station 
 
 The figures of table 16 show that the drop in temperature from 
 109.2° F in 1929 to 105.6° F in 1930 was accompanied by a reduction 
 in the palatability score of Thompson Seedless in the Coachella 
 Valley of 35 per cent at 17° Balling, 41 per cent at 18° Balling, and 
 24 per cent at 19° Balling. The further reduction in the mean maxi- 
 mum temperature for the thirty-day period before harvesting to 
 97.9° F in 1931 reduced the score 61 per cent at 17° Balling, 71 per 
 cent at 18° Balling, and 37 per cent at 19° Balling below the score 
 of 1929. The influence of the seasonal conditions of the Coachella 
 Valley on the palatability scores of the Malaga at 17°, 18°, and 19° 
 Balling was similar to that of the Thompson Seedless. 
 
 In Kern County the mean maximum temperature for the forty 
 days before harvesting was almost the same during 1929 and 1930. 
 In these seasons the palatability scores at the degrees Balling indicated 
 also were almost the same. In 1931, however, when the mean maxi- 
 mum temperature was only 96.3° F there was a reduction in the 
 palatability score of 33 per cent at 17° Balling, 21 per cent at 18° 
 Balling, and 18 per cent at 19° Balling. 
 
 For Fresno County where the temperature for the period before 
 harvesting was higher in 1931 than in 1929 and 1930 the palatability 
 score also was higher. This increase accompanying the 10.2° F 
 increase in the mean maximum temperature was 110 per cent at 17° 
 Balling, 100 per cent at 18° Balling, and 50 per cent at 19° Balling. 
 
 The figures of tables 17 and 18 indicate the extent to which the 
 palatability score of grapes of the same degree Balling was influenced 
 by regional and seasonal conditions. They clearly show that so long 
 as grapes are grown in regions which differ climatically, and so long 
 as seasons vary, degree Balling alone cannot be expected to serve 
 perfectly as a means of measuring palatability. 
 
 In the past the state was divided into two regions for the purpose 
 of increasing the efficiency of degree Balling as a means of meas- 
 uring maturity. Such a division might improve the accuracy of 
 this means as a measure of eating quality to some extent, provided 
 that sufficient differences are made in the degree Balling requirement 
 for the different regions. It would, however, never achieve entirely 
 satisfactory results since it removes only the influence of regional 
 conditions. The influence of seasonal conditions would continue to 
 move the palatability score which indicates the lower limit of good 
 eating quality through the ripening range of 16° to 20° Balling, thus 
 nullifying our best efforts to make degree Balling a workable means 
 of measuring maturity. 
 
Bul. 529] Maturity Tests for Table Grapes 31 
 
 THE BALLLING-ACID RATIO AS A MEANS OF MEASURING 
 
 MATURITY 
 
 The conditions which have been largely responsible for the failure 
 of either per cent acid or degree Balling used alone as a means of 
 measuring maturity in the sense of eating quality indicate that 
 these means might give promise if used in combination. In combina- 
 tion these composition factors embrace the very high correlation of 
 degree Balling and palatability as well as the condition of fluctuating 
 acidity which has been principally responsible for the partial failure 
 of the degree Balling standard. The Balling-acid ratio of the ex- 
 pressed juice of the grapes is obtained by dividing the degree Balling 
 (per cent total solids) by the per cent acidity. The relation of these 
 two factors to one another has long been known to influence greatly 
 the palatability of grapes. In the past, however, sufficient data to 
 indicate the utility of this relation or ratio as a means of measuring 
 maturity have been lacking. 
 
 The efficiency of the Balling-acid ratio as a means of measuring 
 maturity can be indicated by applying it to the samples of fruit that 
 have been used in this investigation. For this purpose the samples 
 are divided on the basis of the Balling-acid ratio indicated for each 
 variety in table 17. All fruit meeting this ratio was admitted irre- 
 spective of its palatability score. Some of this fruit may have had a 
 score of less than 25 (fair) ; if so, it was listed with the samples of 
 poor fruit admitted by this test. Fruit having a palatability score 
 of 37 or more was admitted even though its Balling-acid ratio was 
 not equal to or above that indicated for the variety. If its Balling- 
 acid ratio was below that indicated, such fruit was listed among the 
 samples of good fruit excluded by this test. Fruit having a palata- 
 bility score between 25 and 37 was admitted when its Balling-acid 
 ratio was equal to or above that indicated and excluded when the 
 ratio was below that indicated for the variety in table 17. This latter 
 fruit is marginal. Its inclusion or elimination was immaterial so 
 far as the Balling-acid ratio test is concerned. It maiy be considered 
 as gcod to eat by those who like their fruit tart. It would be con- 
 sidered poor by those who like their grapes sweet. The results 
 obtained on this basis with the Balling-acid ratio as a means of 
 measuring maturity in relation to eating quality are shown in table 17. 
 
 The figures of table 17 show the very high degree of efficiency with 
 which the poor fruit was excluded by the Balling-acid ratio test. In 
 the case of Ohanez and Cornichon 7.5 and 7.0 per cent, respectively, of 
 
32 
 
 University of California — Experiment Station 
 
 poor fruit was admitted. From these figures the amount of poor fruit 
 admitted in the other varieties varied downward to 1.0 per cent in 
 Muscat, The average amount of poor fruit admitted by this test for 
 all the varieties was 2.5 per cent. 
 
 This exclusion of poor fruit was affected without the loss of an 
 appreciable amount of good fruit. In Emperor 1.1 per cent of good 
 fruit was excluded. In no other variety did the elimination of good 
 fruit amount to as much as 1 per cent. For the eleven varieties the 
 loss of good fruit by this test amounted to 0.4 per cent. 
 
 TABLE 17 
 The Balling-acid Batio as a Means of Measuring- Maturity in Belation to 
 
 Palatability 
 
 Variety 
 
 Thompson Seedless 
 
 Malaga 
 
 Ribier 
 
 Emperor 
 
 Ohanez 
 
 Muscat 
 
 Cornichon 
 
 Tokay 
 
 Molinera (Red Malaga) 
 
 Olivette Blanche 
 
 Rish Baba 
 
 Number 
 of samples 
 collected 
 
 875 
 760 
 325 
 460 
 120 
 200 
 
 72 
 492 
 260 
 
 48 
 
 Balling- 
 acid 
 ratio 
 
 25:1 
 25:1 
 25:1 
 30:1 
 30:1 
 30:1 
 30:1 
 35:1 
 35:1 
 35:1 
 40:1 
 
 Fruit 
 
 scoring poor 
 admitted 
 
 per cent 
 
 2.0 
 
 2 
 
 5 
 
 1 
 
 5 
 
 3 
 
 7 
 
 7 
 
 5 
 
 1 
 
 
 
 7 
 
 
 
 1 
 
 4 
 
 3 
 
 5 
 
 2 
 
 
 
 3 
 
 
 
 Fruit scoring 
 
 fair or better 
 
 excluded 
 
 per cent 
 0.0 
 0.7 
 
 1.1 
 
 5 
 
 8 
 0.0 
 
 
 
 The figures of table 17 do not fully show the effectiveness with 
 which the Balling-acid ratio indicated serves as a means of excluding 
 sour grapes. The majority of the samples of poor fruit admitted by 
 this test were poor because they were flat or insipid and not because 
 they were green or high in acid. Of the poor fruit admitted 85 per 
 cent was of this character. Therefore, this test admitted only 0.38 
 per cent of sour or immature fruit. 
 
 None of the tests have excluded the flat or insipid fruit. The 
 samples included in this investigation were collected with the view 
 of making the range of sampling more complete. Fortunately, in 
 actual harvesting and packing operations this fruit would usually be 
 eliminated because of its soft texture and its dull lifeless appearance. 
 
 The superiority of the Balling-acid ratio to degree Balling alone 
 as a means of measuring maturity is indicated by the figures of table 
 17 as compared to the figures of tables 12, 13, and 14. The present 
 degree Balling requirement admitted an average of 20.0 per cent of 
 
! 
 
 Bul. 529] Maturity Tests for Table Grapes 33 
 
 poor fruit for the eleven varieties. It excluded 0.7 per cent of good 
 fruit, The Balling-acid ratio admitted only an average of 2.5 per cent 
 of poor fruit and excluded only 0.4 per cent of the good fruit, To 
 raise the degree Balling requirement 2° reduced the amount of poor 
 fruit admitted to an average of 5.8 per cent for the eleven varieties ; 
 however, it excluded 12 per cent of the good fruit. 
 
 Accompanying its superiority over degree Balling as a means of 
 separating the good grapes from those that are sour the Balling-acid 
 ratio is not affected by climatic (regional and seasonal) conditions. 
 In very hot regions where the acidity is low and where grapes become 
 palatable at a relatively low sugar content the low acidity enables the 
 grapes to meet the Balling-acid ratio requirement at a relatively low 
 degree Balling. In the cooler regions, on the contrary, where the 
 acidity is higher, and where higher quality is possible owing to the 
 higher acid content, the grapes must be left on the vines until they 
 have attained a higher degree Balling in order to meet the Balling- 
 acid ratio requirement. In a similar manner the Balling-acid ratio 
 requirement will take care of the fluctuation in acidity which is 
 brought about by hot and cool seasons. 
 
 A SUGGESTED MEANS FOR DETERMINING THE MATURITY OF 
 
 TABLE GRAPES 
 
 Of the considerable number of samples used in this investigation 
 practically no grapes scoring fair or better in eating quality were 
 excluded by the minimum degree Balling requirement indicated in 
 table 18. Thus, a degree Balling requirement which is equivalent to 
 the lower limit of the ripening range of the varieties used can be 
 employed to obviate the need of making an acidity determination on 
 fruit of this degree Balling or less. Within the ripening range — from 
 the degree Balling indicated in table 18 up to 20° Balling — the degree 
 Balling and the per cent acid should both be determined, so that the 
 Balling-acid ratio may be used to interpret the maturity of the 
 fruit in relation to its palatability. Above 20° Balling, again, the 
 degree Balling test alone is sufficient. Only a very limited amount of 
 fruit of 20° and higher Balling was found to be poor in eating quality 
 in these tests. It is negligible. Also above 20° Balling the Balling-acid 
 ratios which have been found to apply in the ripening range do not 
 always fit. This is owing to masking of the acid taste by the relatively 
 hif^h percentage of sugar. 
 
 The requirements of this method of measuring maturity are shown 
 in table 18. 
 
34 
 
 University of California — Experiment Station 
 
 The different Balling-acid ratio requirements shown for the four 
 groups of varieties are necessary owing to the varietal differences in 
 the relation of degree Balling to acidity. The difference is largely in 
 the per cent acidity of the varieties. This does not seriously compli- 
 cate the utilization of this means of determining maturity since the 
 ratio for the individual varieties will be the same for the entire state. 
 
 TABLE 18 
 
 A Suggested Standard of Maturity for 
 
 Table Grapes 
 
 Variety 
 
 Minimum 
 
 degree 
 
 Balling 
 
 requirement 
 
 Balling-acid 
 
 ratios for fruit 
 
 up to 20° 
 
 Balling 
 
 
 17 
 17 
 16 
 17 
 17 
 17 
 17 
 17 
 17 
 16 
 16 
 
 25:1 
 
 
 25:1 
 
 Ribier 
 
 25:1 
 
 Ohanez 
 
 30:1 
 
 
 30:1 
 
 
 30:1 
 
 
 30:1 
 
 
 35:1 
 
 
 35:1 
 
 
 35:1 
 
 
 40:1 
 
 
 
 SUMMARY 
 
 During the seasons of 1929, 1930, and 1931 more than 3,000 sam- 
 ples of the leading table grape varieties in the ripening range, i.e., 
 from poor to good in eating quality, were collected from all of the 
 principal districts of the state in which they are grown. Each sample 
 was scored for eating quality by at least six individuals, The samples 
 were then pressed and the degree Balling and per cent acidity of the 
 juice obtained. 
 
 The influence of regional conditions on the composition and palat- 
 abilitjy of grapes was indicated by a comparison of the samples col- 
 lected in the three regions, Coachella and Imperial valleys, Kern 
 County, and Fresno-to-Davis. The fruit of the same degree Balling 
 was considerably higher in acidity in the region Fresno-to-Davis than 
 in the Coachella and Imperial valleys. The fruit of Kern County 
 was intermediate in acidity. Owing to this difference in acidity it 
 was found that the sugar content of fruit of Kern County had to be 
 about 1° Balling higher and the fruit of the region Fresno-to-Davis 
 
Bul. 529] Maturity Tests for Table Grapes 35 
 
 about 2.5° Balling' higher than that of the Coaehella and Imperial 
 valleys if the fruit of all three regions was to be of the same relative 
 eating quality. 
 
 The influence of differences in the seasonal temperatures on com- 
 position and palatability was very similar to that of the different 
 regional conditions. In cool seasons the acidity was relatively high in 
 relation to degree Balling and in hot seasons it was relatively low. 
 Thus, in hot seasons the fruit became palatable at a lower degree 
 Balling than in cool seasons. 
 
 The acidity of the expressed juice of grapes is correlated with 
 their eating quality. This correlation with eating quality, however, is 
 not sufficiently marked to serve as a means of measuring maturity. 
 
 The Balling reading of the expressed juice of grapes has a very 
 high degree of correlation with eating quality. If regional and sea- 
 sonal conditions were constant, the degree Balling of the expressed 
 juice would serve well as a measure of maturity. Owing, however, to 
 the variations in regional and seasonal conditions which very mate- 
 rially influence the relation of acidity to sugar content the Balling 
 reading alone is not a reliable measure of maturity in relation to 
 eating quality. 
 
 To raise the present degree Balling requirement would exclude 
 more of the poor fruit, but such a revision would prove very costly 
 in forcing the delay of harvesting of much palatable fruit, especially 
 in hot seasons. 
 
 By combining degree Balling and per cent acidity of the expressed 
 juice in the form of a Balling-acid ratio an index of maturity was 
 obtained which embraces the very high correlation of degree Balling 
 and eating quality as well as the condition of fluctuating acidity. The 
 Balling-acid ratio has shown promise as a means of excluding poor 
 fruit without also forcing the delay of harvesting of certain good 
 fruit. 
 
 A means for determining the maturity of table grapes by using 
 the degree Balling and the Balling-acid ratio of the expressed juice 
 
 is suggested. 
 
 ACKNOWLEDGMENT 
 
 It is a pleasure to acknowledge the cooperation of many growers 
 in the various regions who supplied the grapes for these tests. Much 
 credit for the success of this study is also due the group of individuals 
 who tasted the samples and scored them for eating quality, and to Mr. 
 W. C. Condit, who assisted in the collection of most of the samples 
 and who made many of the determinations. 
 
 13m-6,'32