gj SB 295 .H8 R8 Copy 1 SB 295 .H8 R8 Copy 1 s^.^'^^o. ) STATES DEPARTMENT OF AGRICULTURE BULLETIN No. 282 Contribution from the Bureau of Plant Industry WM. A. TAYLOR, Chief Washington, D. C. PROFESSIONAL PAPER August 11, 1915 A STUDY OF THE SOFT RESINS IN SULPHURED AND UNSUL- PHURED HOPS IN COLD AND IN OPEN STORAGE. By G. A. Russell, «• Expert, Drug-Plant and Poisonous-Plant Investigations. CONTENTS. Page. Introduction 1 Preparation of the hops studied 2 Changes in physical appearance 3 Moisture content and changes in the propor- tion of soft and hard resins 4 Changes in the composition of the soft resins . . 10 Chemical values of the soft resins 15 Summary 18 INTRODUCTION. During the past decade the soft resins of hops have been the sub- ject of numerous investigations wliich have dealt almost exclu- sively with the percentage of yield and the methods of extraction. With the exception of the work of Fischer/ no statements have been found in the literature to show that recognized chemical methods have been used to determine the changes which occur in the soft resins of hops subsequent to harvesting. The effect of refrigeration on the physical condition and on certain chemical constituents of sul- phured and unsulphured hops has been studied by Stockberger and Rabak/ who gave special consideration to the changes which occur in the volatile oil. Aside from the changes noted by these authors, extensive modifications also occur in the soft resins of hops, the character of which may be determined through the use of reliable analytical methods. 1 Fischer, Alfred. Analysis of hops as a basis for their valuation. In Pure Products, v. S, no. 10, p. 5.36-538. 1912. 2 Stockberger, W. W., and Rabak, Frank. Some effects of refrigeration on sulphured and unsulphured hops. U. S. Dept. Agr., Bur. Plant Indus. Bui. 271, 21 p. 1912. Note.— This bulletin presents the results obtained from experiments conducted to determine the extent and character of the changes in the soft resins in hops under varying conditions of curing and storage. The soft resins, or so-called bitter aci4s, are a principal factor in determining the commercial value of hops. 98657°— Bull. 282—15 1 Ml z y^-'. ^^ 2 BULLETIN 282, V. S. DEPARTMENT OF AGEICULTURE. In order to obtain additional data regarding the effect of various storage conditions upon the soft resins of sulphured and unsulphured hops, a quantity of material was prepared and held under observa- tion for several years. The data secured indicate that there is a marked chemical rearrangement or balancing of at least a part of the components of these resins during the first year after the hops are harvested. This rearrangement is most marked in hops kept in cold storage, and of these it is most evident in the unsidphured hops. It is generally conceded that the commercial value of hops is almost entirely contingent upon two considerations, namely, the character of the aroma and the nature and quantity of the soft resins. At the last International Hop and Barley Exhibit, held in Chicago in 1911, the score card gave an equal rating to aroma and to the soft resins, or, as they are sometimes termed, the hop bitter acids. Although sulphuring and cold storage are efficient factors in retard- ing the diminution of the quantity of soft resins in hops, they do not prevent chemical changes from taking place therein. Nevertheless, the data obtained by the study of these changes indicate that they are influenced to a considerable degree by both sulphuring and cold storage. The experiments detailed in the following pages were made with a view to determining the extent and character of these changes. PREPARATION OF THE HOPS STUDIED. Since soil and climate, as well as other factors, are undoubtedly responsible for the varying quantity of soft resins found in hops of different geographical origin, all the samples of hops used in this investigation were secured from a common source, in order to elimi- nate variation so far as possible. Accordingly, two lots of hops harvested from the same field at Perkins, Cal., in September, 1911, were dried in ordinary hop kilns, one portion without being sulphured, the other receiving the customary sulphuring in the early stages of drying. Duplicate samples of each lot were then placed in hermeti- cally sealed tin cans and shipped to Washington, D. C. About the 1st of December one sample each of the sulphured and unsulphured hops was subjected to analysis, and the remaining samples, each weighing 2 kilograms, were then removed from the tins, compressed to about the same degree as the hops in a commercial bale, and com- pletely inclosed in a cover of ordinary hop sacking. Three each of those sulphured and unsulphured samples were then placed in cold storage in the hop storeroom of a local brewery, and a similar set of samples was placed in the attic of a frame building at the Arlington Experiment Farm, Virginia. On December 1 of each of the three f ol- lov/ing years one sample each of the sulphured and the unsulphured hops was withdrawn from cold and open storage, respectively, and subjected to analysis. a «F a. AUa 2.(1 ''9^5 r" SOFT RESINS IN SULPHURED AND UNSULPHURED HOPS. CHANGES IN PHYSICAL APPEARANCE. > On receipt of the various samples of hops from Perkins, Cal., in 1911, they were examined and the following notes taken respecting their physical characteristics: Sulphured hops in the original lot. — Fine fresh hop flavor; oily feeling; h:pulin sticky; aroma excellent; color bright, characteristic of new fresh hops; color of lupiJin bright. Unsulphured hops in the original lot. — Fine fresh hop flavor; oily feeling; Ir.pulin sticky; aroma excellent; color bright, characteristic of new fresli hops, thorgh some- what greener in appearance than the corresponding snlphitred sample; color of Ir.pr.lin bright. (3n December 1 of the three following years, two samples each from cold and from open storage were examined and the following notes were taken on their physical characteristics: Sulphured hops in cold storage one year. — Fresh hop flavor; oily feeling; lupnlin sticky; aroma good; color darker than the original sample, not so briglit and charac- teristic; color of lupulin bright. Unsulphured hops in cold storage one year. — Fresh hop flavor; oily feeling; lupulin sticky; aroma good; color much darker than the original sample, not so bright and characteristic; color of lupulin bright. Sulphured hops in open storage one year. — Strawlike flavor; oily feeling; lupulin less sticky; aroma disagreeable; color dull, bright color ha\ing disappeared; color of lupulin dull. Unsulphured hops in open storage one year. — Strawliko flavor; oily feeling less notice- able; lupulin less sticky; aroma disagreeable; color A^ery dull; color of lupulin dull. Sulphured hops in cold storage two years. — Decided strawlike flavor; oily feeling very slight; lupulin slightly sticky; aroma slightly hoplike; color dark yellow, brightness having disappeared; color of lupulin dull. Unsulphured hops in cold storage two years. — Most decided strawlike odor, somewhat musty; oily feeling practically gone; lupulin not sticky; aroma like musty straw; color dark brownish yellow; color of lupulin very dull. Sulphured hops in open storage two years. — Decided strawlike flavor; oily feeling practically gone; lupulin slightly sticky; aroma that of musty straw; color dark brown- ish yellow; color of lupulin very dull. Unsulphured hops in open storage two years. — Very decided musty flavor; oily feeliu"- gone; lupulin very slightly sticky; aroma that of musty straw; color dark brov.'nish yellow; color of lupulin very dark and dull. Sulphured hops in cold storage three years: — Most decided strawlike flavor, somewhat musty; oily feeling gone; lupulin very slightly sticky; aroma that of old musty straw; color dark brownish yellow; color of lupulin A^ery dark and dull: hop cones falling apart. Unsulphured hops in cold storage three years. — Very decided musty, strawlike fluAor; oily feeling entirely gone ; lupulin not sticky ; aroma that of old musty straw ; color Aery dark, dirty brownish yellow; color of lupulin very dark and dull; hop cones falling apart. Sulphured hops in open storage three years. — Very decided musty, strawlike flavor; oily feeling entirely gone; lupulin not sticky; aroma that of old musty straAV; color dark broAvnish yelloAv; color of lupulin very dark and dull; hop cones fallen ajjart. Unsulphured hops in open storage three years. — Most decided musty, straAvUke flavor; oily feeling entirely gone; lupulin not sticky; aroma that of old musty straw; color A'ery dark brownish yellow; color of lupulin A-ery dark and dull; ho]i cones fallen apart. 4 BULLETIN 282, U. S. DEPARTMENT OF AGEICULTTJRE. As far as physical valuation indicates, the sulphured hops in cold storage deteriorated at a slower rate than the unsulphured hops, and the same is true for the samples placed in open storage. At the end of one year of storage very little phj^sical difference could be noticed in the cold-storage hops other than that the color had darkened in both the sulphured and unsulphured samples, more especially in the latter. The samples in open storage at the end of one year had each developed a strawlike odor and had become dull in color. The lupulin of both the sulphured and unsulphured hops had begun to lose its brightness and its sticky feeling. At the end of the second year of storage a most decided change had taken place in all the samples. The sulphured hops in cold storage had developed a strawlike flavor and a dry feeling and the bright color had disappeared. The unsulphured samples had developed a musty odor and an extremely dry feeling, and the characteristic greenish yellow color had disappeared. The unsulphured hops had deteriorated more rapidly than the corresponding sulphured hops. So far as the physical valuation indicated, the hops in open storage had deteriorated to a much greater degree than the hops in cold storage. The unsulphured samples in open storage had become very musty in odor and very dark in color, in addition to losing their crisp and sticky feeling. At the close of three years of storage the samples had lost all traces of hop flavor and had developed a musty, strawlike odor. A slight stickiness could still be detected in the sulphured hops in cold storage. The hop cones in the cold-storage samples had fallen apart to some extent, whereas those in the open storage samples had completely fallen apart. The lupulin in all the samples was much discolored. MOISTURE CONTENT AND CHANGES IN THE PROPORTION OF SOFT AND HARD RESINS. At the time the hops were received m Washington a sample each of the sulphured and unsulphured hops was analyzed and the results thus obtained were used as the basis for comparing the analyses which were made of the various samples during each year of storage. MOISTURE CONTENT. For the determination of the moisture content 12 grams of hops were taken from each of the samples under investigation, dried over sulphuric acid until of constant weight, and the loss in weight returned as moisture. The moisture content of the original hops and of the hops in both cold and open storage for the several years is given in Table I. SOFT RESINS IN SULPHURED AND UNSULPHURED HOPS. Table I. — Moisture in the original samples of sulphured and unsulphured hops and in samples hept in cold and in open storage. Treatment at the kiln. Original sample, 1011. Cold storaKC Open storage. 1012 1913 1914 1912 loi:! 1914 Sulphured Unsulphure.d Per cent. 6. IS 5.23 Per cent. 11.04 10. SO Per cent. 11.04 10.79 Per cent. 9.83 10.90 Per cent. 5.81 6.14 Per cent. 6.37 5.90 Per cent. 6.40 5.50 From Table I it is evident that the moisture content of the hops kept in cold storage was greater than of those in open storage. In the samples kept hi cold storage the moisture content was very uniform for the three years in both the sulphured and the unsul- phured hops, indicating that the cold-storage room was kept at a uniform temperature throughout this pericnl. In the open-storage samples a slight fluctuation in the moisture content was evident, due apparently to differences m the atmospheric conditions at the time the samples were removed for analysis. Since moisture is an imjior- tant adjunct to a great many chemical changes, it is probable that the greater quantity found in the samples kept in cold storage had a direct bearing on the chemical changes that took place in the soft resins. SOFT RESINS. In determining the quantity of soft resins hi the hop samples, a departure was made from the method usually employed. A kilo- gram of hops was extracted by maceration and percolation with petroleum ether (B. P. 35° C. to 70° C). Two macerations were necessary to complete the extraction. The mixed percolates were then heated on a water bath at 70° C. and the major portion of the petroleum ether recovered. The remainder of the petroleum ether was allowed to evaporate spontaneously and the weight of the residue returned as soft reshis. The residues each contained a small fraction of approximately 0.4 per cent of wax, which for purposes of com- parison may be disregarded. The percentage of soft resins in the original sulphured and unsulphured samples and in the corresponding samples in cold and in open storage is shown in Table II. Table II. -Soft 7-esins in the original samples of sulphured and unsulphured hops and in samples kept in cold and in open storage. Treatment at the kiln. Original sample, 1911. Cold storage. | Open stora;-:c. 1912 1913 1914 1912 19i:i 1914 Sulphured Unsulphured Per cent. 12.32 11.17 Per cent. 11.91 9.72 Per cent. 11.46 8.66 Per cent. Per cent. 4.98 11.32 3.81 S.73 Per cent. 9.03 7.43 Per cent. 3.20 2.32 BULLETIN 282, U. S. DEPAETMENT OF AGRICULTURE. Regarding, first, the sulphured hops, the data in Table II show that the percentage of soft resins decreased somewhat during the first and second years of storage and very rapidly during the third year. The decrease was less, however, in the cold-storage samples than in those kept in open storage. The unsulphurcd hops show a marked decrease from year to year, the decrease being most pro- nounced in the third year of storage. The unsulphured samples in open storage show a greater loss than the corresponding samples kept in cold storage. Durmg the first year of open storage the soft-resin content in the sulphured hops decreased less rap- idly than in the un- sulphured hops, but more rapidly in the following two years. It will be observed from figure 1 that the quantity of soft resins present in the sulphured hops in both cold and open storage decreased during each year and that the decrease was especially marked during the third year of storage. Figure 1 also shows that the unsulphured hops in cold storage decreased in soft-resin content more rapidly than the sulphured hops and that this decrease was rapid during the first year, less pronounced during the second year, and at the end of the third year gradually ap- proached the same point of value as in the sulphured hops in cold storage. The soft-resin content of the misulphured hops in open storage decreased at about the same rate as that of the sulphured hops in open storage. The percentage of decrease in soft resins during the three years, as compared with the original samples, is given in Table III. y^C/iffS //V STORAGE Fig. 1.— Curves of the percentage of soft resins in sulphured and un- sulphured hops in cold and in open storage. SOFT RESINS IN SULPHURED AND UNSULPHURED HOPS. 7 Table III. — Decrease in the soft resins of sulphured and unsulphured hops in cold and in open storage compared with the soft-resin content of the original samples. Original sample, 1911. Cold storage. Open storage. 1912 1913 1914 1912 1913 1914 Sulphured Unsulphured . . Per cent. 100 100 Per cent. 3.32 12.98 Per cent. 6.98 22.47 Per cent. 59. 57 65.89 Per cent. 8.11 21.84 Per cent. 26.71 33. 48 Per cent. 74.02 79.23 From Table III, in which the soft-resin content in the origintil samples is considered as 100 per cent, it is evident that the decrease in the sulphured hops during the first two years in cold storage was not great, but it was rapid during the third year. In open storage the decrease was very pronounced during each year. The unsul- phured hops in cold storage show a marked decrease, which was gi-eatest in the third year, and in open storage the decrease was even more pronounced year by year. HARD RESINS. The hard resins in the various samples of hops used in this study were also determined. A portion of tlie hops after being extracted with petroleum ether was again extracted with ether, the ether recovered, and the weight of the residue returned as hard resin. By this method an extra calculation is necessarj^, but in using large quantities of hops the time consumed is more than compensated for in the accuracy obtained. The hard-resin content of the various samples is shown in Table IV. Table IV. — Hard resins in the original samples of sulphured and unsulphured hops and in samples kept in cold and in open storage. Treatment at the kiln. Original sample, 1911. Cold storage. Open storage. 1912 1913 1914 1912 1913 1914 Per cent. 5.26 6.43 Per cent. 6. .53 8.35 Per cent. 8.97 10. 08 Per cent. 9.90 10.05 Per cent. 8.32 9.53 Per cent. 9.09 10. 45 Per cent. 10. 10 10.46 The figures in Table IV give an index of the change in the quantity of hard resins that took place in the various hop samples. The greatest change occurred in the unsulphured hops in open storage and the least change in the unsulphured hops during the first two years in cold storage. The difference in the content of hard resins of both sulphured and unsulphured hops in cold and in open storage, respectively, became materially less in the third year of storage and probably indicates that the changes which took place in the hops 8 BULLETIN 282, U. S. DEPARTMENT OF AGEICULTURE. tended to reach a state of equilibriiun irrespective of the treatment of the sample. Figure 2 gives a graphic representation of the increase in the hard- resin content of sulphured and unsulphured hops in cold and in open storage. During the first year the increase in the hard-resin content in the sulphured hops was greater in open storage than in cold storage. -Vt the end of the second year the sulphured hops in both cold and open storage con- tained about the same percentage of hard resms. The unsulphured hops followed the same lines, but did not present quite so marked a difference durmg the first year of storage. At the end of the third year the hard-resin content m all the samples had become uniform and a state was reached where the increase, if any, was very slow. Table V gives the percentage of mcrease in the hard-resin content of the various samples as compared with the original, the hard-resin content of the latter ])eing considered as 100 per cent. Table V. — Increase in the hard resins of sulphured and unsulphured hops in cold and in open storage, compared with the hard-resin content of the original samples. y£^/?S //y STOPAGE -Curves of the percentage of hard resins in sulphured and un- sulphured hops in cold and in open storage. Treatment at tlie kiln. Original sample, 1911. Cold storage. 1912 Open storage. Sulphured l^nsulphured. Per cent. 100 100 Per cent. 24.14 29.85 Per cent. 70.53 52.75 Per cent. 88.21 56.29 Per cent. 58. 17 48. 21 Per cent. 72.81 62.51 Per cent. 92.01 62.67 The sulphured hops appeared to react less readily to changes that brmg about an increase in the hard resins. From this it is uif erred that sidphm-mg is a factor that retards the changing of soft resms to hard resins. This is shown most emphatically in Table V by the fact that the percentage of increase in the misulphured hops was much less in both cold and open storage than in the corresponding sulphured SOFT EESINS IN SULPHURED AND UNSULPHUKED HOPS. 9 hops. A further study of Tabh^ V mdicates that a combination of sulphuring and cokl storage was most effective in retardmg the changes that produce hard resins. TOTAL RESINS. The total resin content of the various hop samples, found by adding the soft resins and tlie hard resins together, is shown in Table Yl. Table VI. — Total resins in the original samples of sulphured and unsulpJiured hops and in samples kept in cold and in open storage. Treatment at the kiln. Sulphured Unsulphured. Original sample, ion. P(r cent. 17. 58 17.60 Told storage. Per cent. 18. -14 18. 07 Per cent. 20. 43 18. 74 Per cent. 14. 88 13. 86 cipen storage. Per cent. 19.64 18.26 Per cent. IS. 12 17.88 Per cent. 13.30 12. 78 From the figures in Table VI it appears that some tliscrepancies exist, since the total resins in some years ran higher than those of the original sample. Experiments in this laboratory have shown that two samples are rarely ever the same in total yield of resms ; hence, no weight need be attached to the apparent discrepancies. The sudden decrease in the total resins in all the samples in the year 1914 is of special interest. Up to this point the hops in storage had retained approximately their original content of soft resms. A marked diminution now occurred in the content of soft resms, which is not compensated by a corresponding increase in the content of hard resins. It appears from the data at hand that a portion of the soft resins had been transformed into a compound or compounds insoluble in ether or in petroleum ether, since the marked loss in percentage of soft resms does not appear in the ether extract. The extent of the change was greatest in the unsulphured hops in open storage and least in the sulphured hops in cold storage, but m all samples, irrespective of treatment either at the kiln or during storage, the decrease was rapid. Table IV shows that at the end of the second year of storage a point was reached by all the samples beyond which the hard resins did not materially increase. Nevertheless, at this point the soft resins began to decrease most rapidly. Although pre- vious investigators have stated that the soft resins change entirely to hard resins, it is probable that only a small portion of the soft resins undergoes such a change, and the remamder is changed into a compound or compounds insoluble in the solvents used m extraction and for that reason is lost sight of in the analysis. 98657°— Bull. 282—15 2 10 BULLETIN 282^ U. S. DEPARTMENT OF AGRICULTURE. Table VII. — Soft resins in the original samples of sulphured and unsulphured hops and in samples kept in cold and in open storage, calculated with reference to the totnl resins. Treatment at the kiln. Original sample, 1911. Cold storage. Open storage. 1912 1913 19H 1912 1913 1914 Sulphured Per cent. 70.13 63.46 Per cent. 64.59 53. 79 Per cent. 56.08 46.21 Per cent. 33.47 27.49 Per cent. 57.63 47. 80 Per cent. 49.83 41.55 Per cent. 24.06 18.15 The data in Table VII show that the sulphured cold-storage hops retained a greater percentage of soft resins each year than did any of the other samples. The unsulphured hops in cold storage and the sidphured hops in open storage contained year by year practically the same percentage of soft resins, as calculated with reference to the total resins. The greatest decrease is noted in the soft resins from the unsulphured hops in open storage. CHANGES IN THE COMPOSITION OF THE SOFT RESINS. That chemical changes take place in the soft resins of hops is a foregone conclusion. In order to study these changes, methods in general use in chemistry, with some modifications, were applied to the soft resins with satisfactory results. The physical properties of color and odor presented in Table YIII were observed from year to year. Table VIII. — Physical properties of the soft resins in the original samples of sulphured and unsulphured hops and in samples kept in cold and in open storage. Treatment at the kiln. Original sample, 1911. Cold storage. 1912 1913 1914 Color: Sulphured Greenish brown. Dark brown Aromatic, pleas- ant. do Dark brown Ve r y dark brown. Aromatic, pleas- ant. Aromatic, pun- gent. Greenish brown, do Unsulphured Do. Odor: Aromatic, pleas- ant. Agreeable, hop- like. pleasant. Do. Treatment at the kiln. Original sample, 1911. Open storage. 1912 1913 1914 Color: Greenish brown. Dark brown do Greenish l)rown. do Do. Odor: Sulphured Aromatic, pleas- ant. do . Aromatic, pleas- ant. Aromatic, pun- gent. Aromatic, pleas- ant. Aromatic, pun- gent. Disagreeable, somewhat aro- matic. Do. Unsulphured SOFT EESINS IN SULPHURED AND UNSULPHUEED HOPS. 11 All the samples had an extremely bitter taste, manifested strongly at the base of the tongue when a minute particle of the soft resin was held in the mouth for a few seconds. Tlie color, odor, and taste, which appeal solely to the senses, are of relatively small importance in this investigation. As shown in Table VIII, the color of the soft resins in all cases became darker with the age of the sample examined; the odor became very disagreeable with the decrease of the soft resins and the taste at aU times remained very bitter. The soft resins are fluid in nature, and during the first two years of storage all were of the same consistency. Those extracted in 1914 were more solid and had the consistency of a thick sirup. Owing to their nature, the specific gravity of these resins could not be deter- mined with accuracy. ACro AND ESTER VALUES. The determination of the free acidity or acid value of the soft resins was carried out as foUows: A small quantity of w^eighed soft resin was taken up in 2 c. c. of standardized alcoholic potassium hydroxid and the excess potassium hydroxid titrated back with N/10 hydrochloric acid. The acid value represents the number of milli- grams of potassium hydroxid necessary to completely neutralize the free acids in 1 gram of the soft resins. In determining the ester value of the soft resins a weighed portion was taken up in standardized alcoholic potassium hydroxid and allowed to stand 24 hours in the cold. Complete saponification took place in that length of time. The excess alkali was titrated back with N/10 hydrocliloric acid and the saponification value calculated. This value, minus the acid value, gives the ester value of the soft resins and represents the number of milligrams of potassium hydroxid necessary to completely saponify aU the combined acids in 1 gram of the soft resins. The changes observed in the acid and ester values are shown in Table IX. Table IX. — Acid and ester values of the soft resins in the original samples of sulphured and unsulphured hops and in samples kept in cold and in open storage. Treatment at the kiln. Orisinal sample, 1911. Cold .storage. Open storage. 1912 19i:3 1914 1912 1913 191-1 Acid value: Sulphured 71.80 60.87 97.7 121.78 97.00 67.00 169. 5 71.. 5 87. .50 76.50 191.1 S7.0 80.7 76.2 226.3 207.8 72.5 52.0 122. 5 123.5 61.50 70.00 202.5 158.0 47.0 77.6 Ester value: Sulphured 271.0 Unsulphured 158. 4 12 BULLETIN 282, U. S. DEPAETMENT OF AGRICULTURE. A graphic representation of tlie acid values is given in figure 3. From this figure it will be seen that after the first year of storage the acid value of the soft resins diminished in the sulphured hops and gradually increased in the unsulphured hops. The rise in acid value of the soft resins of the sulphured hops during the first year in cold storage was probably due to the rearrangement that was taking place in these resins; although esters were formed during this period the esterification did not proceed as rapidly as in the following years, with a consequent rise in free-acid value. During the first year of open storage the acid value of the soft resins of the sulphured hops remained about the same and then gradually decreased at a rate proportionate to that of the sulphured hops in cold storage. The formation of esters was slow during the first year of storage and rapid during the next tv\'0 years, reaching a slightly higher value at the end of the third year than in the corresponding sam- ple in cold storage. The unsulphm^ed hops in cold storage yielded soft resins whose acid value constantly increased throughout the pe- riod of storage. The ester value for these soft resms decreased during the first year, then gradually increased durmg the second year, and very rapidly during the third year of storage. In open storage the acid value in the unsulphured hops was slightly less at the end of the fii'st year than in the corresponding original sample. The ester value (fig. 4) remained almost constant, indicating that there was little change in these values during the first year of storage. From this point the acid values from the rmsulphured hops increased gradually, until at the end of the third year of storage about the same degree of acidity was reached. The increase in acidity was, however, most marked in the unsul- phured hops in open storage. The ester values for the soft resins of the unsulphured hops increased after the first year of storage and was most rapid in the cold-storage samples. The acid value of the soft resins from sulphured hops in both cold and open storage gradually diminished at approxhiiately the same rate after one year of storage. The corresponding ester values in- FiG. 3.- y£^/?s //v sro/fyis£ •Acid-value curves of the soft resins in sulpliured anu unsul- phured hops in cold and in open storage. SOFT RESINS IN SULPHURED AND UNSULPHURED HOPS. 13 creased in approximately the same proportion as the acid values diminished . This decrease in the acid ^'*'"" value a n d increase in ester value would indicate that ester- ification took place faster than free acids were formed, the original quantit}' of free acids being prac- tically used up. In other words, the sul- l^huring of hops ap- pears to hasten the formation of esters ui the soft resins but retards the forma- tion of free acids. The acid value of the soft resins from the sulphured hops m both cold and open storage gradual!}' in- creased during the period of storage, and the correspondhig ester value likewise gradually increased, indicatmg that in the unsul- phured hops the for- mation of free acids and of the corre- sponding esters goes on with regularity. SAPONIFICATION VALUE. y£:^/?s //v sro/fy^GS Tig. 4. — Ester-value curves of the soft resins in sulphured and imsul- phured hops in cold and in open storage. K /SO -^ .1^ <^^ .yU>JiS^