HAWAII AGRICULTURAL EXPERIMENT STATION HONOLULU, HAWAII Under the joint supervision of the UNITED STATES DEPARTMENT OF AGRICULTURE AND THE UNIVERSITY OF HAWAII BULLETIN No. 79 METHODS OF EVALUATING THE MACADAMIA NUT FOR COMMERCIAL USE AND THE VARIATION OCCURRING AMONG SEEDLING PLANTINGS IN HAWAII By J. C. RIPPERTON, Chemist R. H. MOLTZAU, Principal Agricultural Aide and D. W. EDWARDS, Junior Chemist UNITED STATES DEPARTMENT OF AGRICULTURE OFFICE OF EXPERIMENT STATIONS For sale by the Superintendent of Documents, Washington, D. C. - - - - Price 15 cents HAWAII AGRICULTURAL EXPERIMENT STATION, HONOLULU [Under the joint supervision of the Office of Experiment Stations, United States Department of Agriculture^ and the University of Hawaii] James T. Jardine, Chief, Office of Experiment Stations. D. L. Crawford, President, University of Hawaii. STATION STAFF AS OF MAY 31, 1937 Administrative O. C. Magistad, Ph. D., Director. H. K. Hee, Junior Administrative Assistant. Agronomy: J. C. Ripperton, M. S., Chemist. J. M. Westgate, M. S., Consultant in Tropical Agriculture. L. D. Whitney, B. S., Asst. Agrono- mist. F. A. I. Bowers, B. S., Prin. Agr. Aide. A. W. Burt, N. D. D., Prin. Agr. Aide. E. Y. Hosaka, M. S., Asst. Biol Aide. M. Takahashi, M. S., Asst. in Agronomy. Animal Husbandry: L. A. Henke, M. S., Animal Hus- bandman. S. H. Work, Ph. D., Assoc. Animal Husbandman. G. W. H. Goo, B. S., Asst. in Animal Husbandry. C. Maruyama, B. S., Farm Superin- tendent. Bacteriolog/, Pathology, and Histology: O. N. Allen, Ph. D., Collaborator in Bacteriology. G. K. Parris, Ph. D., Assoc. Plant Pathologist. Chemistry and Soils: O. C. Magistad, Ph. D., Prin. Chemist. E. M. Bilger, Ph. D., Collaborator in Chemistry. L. A. Dean, Ph. D., Asst. Chemist. D. W. Edwards, M. S., Jr. Chemist. R. R. Thompson, B. S., Sci. Aide. Foods and Nutrition: Carey D. Miller, M. S., Assoc. Professor of Foods and Nutrition. N. P. Larsen, M. D., Collaborator. Martha Potgieter, Ph. D., Assoc. Chemist. Horticulture: J. H. Beaumont, Ph. D., Prin. Horticulturist. G. W. Groff, M. S., Collaborator in Horticulture. W. W. Jones, Ph. D., Asst. Physiolo- gist. J. E. Welch, M.S., Jr. Olericulturist. R. H. Moltzau, Prin. Agr. Aide. J. C. Thompson, B. S., Prin. Sci. Aide. W. B. Storey, B. S., Biol. Aide. Irrigation: H. A. Wadsworth, B. S., Irrigation Engineer and Soil Physicist. Marketing: F. Okumura, B. A., Marketing Assistant. T. O. Frazier, B. A., Sci. Aide. J. Kaneshiro, B. S., Jr. Sci. Aide. Parasitology and Zoology: J. E. Alicata, Ph. D., Parasitologist. 1 C. J. Hamre, Ph. D., Zoologist and Histologist. H. G. Hansen, District Agent. 2 H. J. Spencer, B. A., Asst. Biologist. J. S. Caceres, Collaborator. 1 W. Jordan, Sr. Sci. Aide. W. Ishikawa, B. S., Asst. Biol. Aide. T. H. Hong, M. S., Jr. Sci. Aide. Poultry: C. M. Bice, B. S., Poultry Husband- man. B. A. Tower, M. S., Asst. Poultry Husbandman. F. L. Brown, Asst. Agr. Aide. Substations: R. K. Pahau, B. S., Superintendent Kona Substation. R. A. Lyman, B. S., Superintendent TIalcakala Substation. 1 In cooperation with Territorial Board of Health. 3 In cooperation with U. S. Department of Agriculture, Bureau of Biological Survey. HAWAII AGRICULTURAL EXPERIMENT STATION HONOLULU, HAWAII Cadet the joint supervision of the l NITED 8 I kTES DEF 1RTMENT Of AGRICULTURE and the I n | \ ERS1 I V OF It \\\ MI BULLETIN No. 7!) Washington, I). C. \|>ril 1938 METHODS OF EVALUATING THE MACADAMIA NUT FOR COMMERCIAL USE AND THE VARIATION OCCURRING AMONG SEEDLING PLANTINGS IN HAWAII By .J. C. Hi ppjbrtom , Chemist, H. H. Mmm/m , Principal Agricultural Aide, and I). W. EiDWARDB. Junior ( fit mist l ONTENTS Page race [ntsoduction i Evaluation of nuts from d iiTerent seedling treea The rough-shell and smooth-shell types of mac- from diflerenl localities n; adamia nut - Methods of evaluat inir macadamia nut- Evaluating commercial samples of macadami i uuts by the quahty-jatio method Discussion 21 Summary 23 Literature cited 23 Appendix a 1 ) l\ I Koi) I CTION The macadamia has been grown in Hawaii as isolated trues or small orchards since the time of its introduction about 1892 (7). 1 Not until 1922 was an attempt made to grow the nut for commercial use. A stock company was formed and sizable plantings were made on two islands, Oahu and Hawaii. With this impetus other interests have made appreciable plantings in many locations on the several islands. The present plantings comprise about N()() acres containing about C)(),()()() trees, most of which are less than 15 years old. In 1031 ;i factory was built and machinery, specially developed for processing the macadamia as a roasted vacuum-packed article for the world trade, was installed. At the time this investigation was begun no data existed as to the nature or extent of variation among macadamia seedlings. Plantings in Hawaii have consisted entirely of seedling trees, the seeds being taken from certain of the old trees of the Territory known to yield well and to produce nuts of good quality. The same general situation appears to exist in Queensland and New South Wales, Australia, where the nut is indigenous. Most of the crop comes from the native "bush" and the largest bearing orchards i Italic numbers in parentheses refer to Literature Cited, p. 23. 26S4<; — :;8 1 1 2 BULLETIN 79, HAWAII EXPERIMENT STATION are but a few acres in size. Certain varieties have been named by nurserymen there, but, as far as can be ascertained, these are not based on extensive tests as to bearing, adaptability, or nut quality. The investigations of the Hawaii Agricultural Experiment Station here reported consisted of a study of methods of evaluating the mac- adamia nut from the standpoint of its use as a commercial article in a shelled and roasted form rather than as a table nut in the unshelled form. Such an approach appears justified for a number of reasons. The present trend in the nut trade is strongly in the direction of ex- tracted kernels. Even the thinnest shelled macadamias are difficult to c^ack with ordinary instruments owing to the smooth surface and tough fibrous nature of the shell, while the thick-shelled nuts offer serious obstacles to anything short of commercial machinery. Fur- ther, the flavor of the macadamia is greatly enhanced by proper roasting or oil cooking and salting. The station's investigations show that there is marked variation in kernel quality, and elimination of the inferior kernel is necessary to produce a uniform product. This is best accomplished in a commercial plant. Selection from this standpoint emphasizes the qualities of the extracted kernel which adapt it to processing as a roasted product rather than large size of nut or paper-thin shell, although these are not to be overlooked. Using the methods developed by the station, nuts from the chief bearing orchards have been evaluated. Samples of nuts from individ- ual trees have been tested for several crops. These show the extent to which seedling variation, climate, and type affect the nut char- acteristics. It is believed that these data, together with the methods of evaluation which have been developed, furnish a basis for an ex- tensive study of the several thousand bearing seedling trees of the Territory, looking toward the selection of varieties for top working and further planting material. THE ROUGH-SHELL AND SMOOTH-SHELL TYPES OF MACADAMIA NUTS There are two distinct types of macadamias in Hawaii, the rough- shell type (Macadamia ternifolia) and the smooth-shell type (M. ternifolia var. integrifolia) . 2 Presumably both types were brought in from Australia where the macadamia is indigenous. The present investigation shows that they have marked differences in both vegetative and nut characteristics (pis. 1, 2, and 3). Table 1 gives a comparison of the two. 2 There is some question as to whether the smooth-shell type should be classed as a separate species or as a variety of Macndnmia ternifolia. For the present, and in this bulletin, the arbitrary term "type" is used instead of "species" or "variety." Hawaii As^icultural Experiment Station. Bull. 79 Plate I Hawaii Agricultural Experiment Station, Bull. 79 Plate 2 Two Rough-Shell Types of Macadamia nuts. A, desirable type, ovoid in shape, moderate thickness of shell, and good size kernel; B, undesirable type, elliptical shape, and very thick shell. The rough-shell macadamia is characterized by a knobby surface of the shell and a sweeter flavor of the kernel. Hawaii Agricultural Experiment Station. Bull. 79 Plate 3 Two Smooth -Shell-Type Macadamia Nuts, Showing Their General Spherical Shape and Smooth-Shell Surface and Great Variation in Thickness of Shell The percentage of kernel in different trees ranges from 19 to 42. This type is generally considered superior to the rough-shell for a commercial roasted nut. Digitized by the Internet Archive in 2013 http://archive.org/details/metevalOOunit THE MACADAMIA NUT IN HAWAII 3 Table I. — Tree and nut characteristics of the rough-shell and smooth-shell types of macadamia nut Item Tree: Leaves Bark Wood .structure Susceptibility to insect* Age of initial tn-aririk? (seed- lings). Cnshelled nut: Shape Shell surface Shell tartan Raw kernel: Color Shrinkage Texture Quality Adhesion to shell Ko.i-t.M kernel: Color. Texture Flavor Rough-shell type Excessively spiny; young leaves pink to red in color. Light gray with many lenticels. WVak, resulting in much splitting of branches. Attacked by leaf rollers, mealy- bugs, grasshoppers, aphids, and nut borer. 3 to 4 years Ovoid to elliptical Knobby Tough, coarse, and fibrous Darker kernel; grayish base Considerable Firm; not easily chipped or bruised. Variable Generally loosens readily. Dark brown Firm to hard Pronounce.!, sweei, variable . Smooth-shell type Somewhat spiny, young leaves usually green, rarely pink. Dark gray with fewer lenticels. Fairly strong; much less splitting. Damage negligible except for leaf rollers. 4 to 6 years. Usually spherical. Smooth. More brittle. Clear, white kernel; usually light- colored base. Usually small. Tender; easily chipped and bruised. Generally superior and more uni- form. Often adheres. Light golden. Tender, crisp. Delicate, mild, uniform. While considerable differences exist within each type both as to tree and to nut characteristics, there is no difficulty in differentiating between the two. From the standpoint of a roasted product the dif- ferences are pronounced. In the raw state, the smooth-shell kernel has a rather flat flavor and mealy texture while the rough-shell kernel has a somewhat pleasing sweetish flavor and firm texture. Upon roasting, the smooth-shell nut develops a light-brown color, crisp, tender texture, and a delightful mild nutty flavor, while the rough- shell kernel darkens quickly and develops a somewhat burned variable flavor and harder texture. Public preference for the smooth-shell roasted nut is by no means universal, but because of the greater uni- formity in quality and more desirable field characteristics, the present trend is toward the smooth-shell type. While most of the commercial plantings are of the smooth-shell type, there is a sufficiency of the rough-shell, particularly in the Kona district, to necessitate its inclusion in this investigation. METHODS OF EVALUATING MACADAMIA NUTS 3 INDIRECT METHODS OF DETERMINING THE OIL CONTENT The oil content is of importance in evaluating a nut, not only because . oil is the predominant constituent, but also because it serves as a I criterion of other qualities. Chemical methods of determining the oil content of various products are laborious and time-consuming so that rapid indirect methods have been developed; for example, the re- tractive-index method of determining the oil content of flax (2) and avocados (/), and the Babcock method of estimating the oil in pecans I (5 ). Specific gravity as an indirect means of determining variations in 4 In the station investigation the nuts were brought to air-dry condition. This requires about 3 weeks in j a dry, wdi-\eutilated place. The air-dry moisture content of 3 to 4 percent permits cracking with a mini- mum of damage to the kernels. 4 BULLETIN 70. HAWAII EXPERIMENT STATION chemical composition and quality has been used with a variety of products, for example, to show the starch content of potatoes (4), and the sugar content and maturity of prunes (6). SPECIFIC GRAVITY The macadamia kernel lends itself well to specific-gravity measure- ment, a single nut being of sufficient size to permit individual deter- mination if desired. The specific-gravity method, as finally perfected for the macadamia, was as follows: The kernel was suspended by forcing into it a fine steel wire of about 30 gage (Brown & Sharpe). To insure that there were no air spaces between the halves, the kernel was split and the halves were strung on the wire with the convex surface downward. The macadamia kernel is of such tender texture that the wire penetrates without difficulty and with a negligible rupturing of tissue. One end of the wire was bent into a hook and the nut was suspended on an ordinary analytical balance. It was weighed in air, and then im- mersed in ethyl alcohol of about 95 percent or any other convenient strength. Ethyl alcohol was found to be satisfactory for the purpose. Its specific gravity of 0.8092 (95 percent by volume at 25°/25° C.) is sufficiently less than that of the lightest macadamia kernel (about 0.965) to permit accurate determinations. Imbibition or interaction of nut and alcohol is negligible as judged by the fact that the weight of the kernel remains practically constant during the time required for weighing in alcohol. The volume of that portion of the steel wire which is submerged is a constant factor and too slight to be of conse- quence. The specific gravity of the alcohol solution was checked at intervals during the tests and frequent measurements of temperatures were made for intermediate corrections. The kernel, after specific-gravity determination, was wiped dry and placed in a stream of air at 60° to 70° C. for about 1 hour to remove the last traces of liquid adhering. The oil was then determined by ether extraction in a Soxhlet apparatus for 24 hours. The procedure finally adopted was as follows: The kernel was placed on a 7-cm filter paper and shaved very fine with a sharp knife or razor blade. The filter paper and contents were placed in an alundum thimble and extracted in a Soxhlet apparatus overnight. The kernel was then ground in an agate mortar. Sufficient oil had been extracted so that the material could be ground to a fine powder. It was then replaced in the filter paper and alundum thimble and extraction continued for the re- mainder of the 24-hour period. The oil was dried to constant weight at 100°. Specific-gravity determination has many desirable features as a laboratory method. It is very rapid and requires no special laboratory equipment. The determination of the specific gravity of a single kernel is often of great advantage. The kernel can subsequently be used for determination of oil, sugars, roasting qualities, or any other properties that it is desired to measure. Use of the entire kernel for ether-extract determination simplifies the procedure and increases its accuracy since exact sampling of the ground kernel is exceedingly difficult. Table 2 gives the results of specific-gravity and ether-extract determinations on a series of 34 rough-shell and GO smooth-shell kernels, the nuts being selected at random from commercial samples. THE MACADAMIA NUT IX HAWAII 5 Table 2.— Relation of specific gravity and oil content of macadamia nut kernels KOIGH-SHELL TYPE Oil content Oil content Oil content Dovia- Devia- Devia- Specinc gravit y El OCT Calcu- lated from f i f calcu I'll "■' t Bpecific pr.ivit v Et hiT Calcu- lated from tion of calcu- lated Pjiecific j.'r:i\ it v Et her Calcu- lated from tion of calcu- lated extrac t \ lllll » \tr. 11 1 1 xtract equa- fi|ii'i- tion 1 fr'lin equa- tion 1 frorn° tion 1 et her extntct ct her extract et her extract Per- Per- Per- Per- Per- p,, Per- Per- Per- cent cent cent cent cent cent cent cent cent 0. 9692 B6t 28 *o. ;{9 +0. Of) 0.9914 74 *9 75. 10 0.21 1.0463 61. 55 62. 01 0. 46 .97119 7s 7:< 79. 99 1.26 . w:f Specific gravity/ether extract of the rough-shell and smooth-shell tyi>es, resj natively (see below). The coefficients of correlation of specific gravity and percent oil, calculated from data in table 2, are as follows: Smooth-shell type— r= — 0.979 ±0.005 Rough-shell type— r= —0.985 ± 0.005 The degree of correlation is sufficiently high to permit the use of the specific gravity as a measure of the percentage of oil in macadamia kernels. In figure 1 the best fitting curves which relate specific gravity to percentage of oil are given for the two types. The equa- tions for these graphs are as follows: (1) Smooth-shell type— y= —212.57^+284.70 (2) Rough-shell type— y= -238.35^+311.40 where 7/ = the percent of oil in the kernel and £=the specific gravity of the kernel. 6 BULLETIN 79, HAWAII EXPERIMENT STATION REFRACTIVE INDEX The method described by Coleman and Fellows (2) was used in determining the refractive index of macadamia kernels: A weighed amount of the material is ground in a mortar with a known amount of Halo wax and the index of refraction of the liquid determined. By referring this value to a curve of the refractive indexes of varying proportions of Halo wax and oil of the material being determined, 85 80 75 UJ 70 u. 65 60 55 50 0.96 N < • SM001 "H-SHELL TYPE^ ( o R0UGH-S HELL TYF 1 Z^A 'E \\ vs 1.08 1. 10 0.98 1.00 1.02 1.04 1.06 SPECIFIC GRAVITY OF KERNEL Figure 1.— Relation of specific gravity of macadamia kernels to ether extract. the percent of oil in the Halowax is read off and the percent of oil in the original material calculated. In the construction of this curve, oil was extracted from the smooth- shell type of macadamia kernels with ethyl ether. The oil was dried in vacuo at about 60° C. and filtered through filter paper. Varying amounts of this oil were added to constant amounts of Halowax for refractive-index determination. The Halowax was measured with a pipette, the same pipette being used for all determinations both of the oil and of the kernel. To 5 ml of Halowax weighing 6.06 ± 0.0 1 g weighed amounts of macadamia oil were added to provide a range oi U to '_ ,( .) percent of oil in the mixture ae i efractive index was deter THE MACADAMIA NUT INB IWAI1 7 mined in a water-jacketed Abbe-Zeiss refractonieter, the temperature being maintained at 27.5° C. This refraetometer permitted direet reading to the third decimal place, the fourth place being estimated. The degree of accuracy is correspondingly less than that possible with an instrument of narrower range as used by Coleman and Fellows. The values for index of refraction (N D ) are plotted against corre- sponding percents of oil in the Halowax-oil mixtures in figure 2. The equation for the best fitting curve is (3) y= —497.1 l.r+806. 56 where 7/ = the percent oil in the Halowax-oil mixtures and x=N D , the index of refraction. The curve in the above equation does not hold for all values of as proved by the fact that extrapolation of the equation to 2=1.4651, the index of refraction of pure macadamia-kernel oil, gives values for ?/ of 78 percent instead of 100 percent, its true value. Within the lim- its used, x= 1.57 to 1.03, the true values of y follow the curve very closely. Using the relation- ship given in equation (3), the applicability of the refractive-index method to detennina- t LOU of the oil content of macadamia kernel was next studied. Kernels of the smooth- shell type Were sepa- rated by Specific grav- ity into 7 samples, each containing 1 2 to 15 kernels. Each sample was t h e n fi n el y chopped and thorough- ly mi xed. E t h e r- ex tract determina- tions wei / made as de- scribed under specific gravity. In determining the refractive index, 5 ml of Halowax were measured exactly as in the procedure described in the foregoing section and added to a weighed portion of the kernel in a small porcelain mortar. The mixture was I hen triturated with a pestle for about 10 minutes. A drop of liquid was withdrawn and the refrac- tive index determined. Trituration was then continued until a con- stant reading resulted. For the final reading, a portion of the liquid was passed through filter paper. N D determinations were made in trip- licate and ether extract in duplicate. The results are given in table 3. £ 30 INDEX OF REFRACTION Figlrk 2.— Index of refraction of mixtures of maeadamia nut oil and Halowax in varying proportions. 8 BULLETIN 79, HAWAII EXPERIMENT STATION Table 3.— Comparison of percent of oil by refractive index method with percent ether extract in macadamia kernels Weight of sample (grams) Index of re- fraction at 27.5° C. Proportion of oil in Halowax- oil mixture Proportion of oil in kernel Calculat e f i from equa- tion i Ether ex- tract -L'G V Id LIU 11 of calcu- lated value from ether extract 2 0473 1. 5899 1. 5902 1. 5909 Percent 21.438 21. 325 20. 916 Percent 80. 77 80. 55 80. 10 Percent Percent 2 0403 2.0022 77. 26 Average. 80. 47 77. 26 +3. 21 2 1076 1. 5899 1. 5907 1. 5912 21. 428 21.019 20. 763 78. 45 78. 85 78.29 2 0464 73.76 74. 84 2.0294 Average.. .. 78. 53 74. 30 +4.23 2 1728 1. 5909 1. 5902 1. 5895 20.916 21. 274 21. 632 73. 81 74. 38 74. 70 9 9097 71.28 70. 41 2.2405 Average 74. 30 70. 85 +3. 45 O 071 1 1.5919 1.5911 1. 5893 20. 405 20.814 21. 734 75. 04 75.23 74. 68 9 1 1fi/1 70. 97 71. 27 2.2546 Average 74. 98 71. 12 +3. 86 2 1647 1. 5918 1. 5930 1. 5936 20. 456 19. 843 19. 536 72.03 73. 19 72.61 68. 78 66. 87 2.0273 Average 72.61 67.83 +4. 78 2.0438 1. 5958 1.5940 1. 5908 18.411 19. 332 20. 968 2.1495 67. 60 67.60 66. 12 66. 51 2.3798 Average 67. 38 66. 32 + 1.06 2.1546 1. 5961 1.5949 1.5917 18. 258 18. 871 20. 507 62. 86 62. 35 62.81 2.2618 61.23 61.03 2.4903 62. 67 61. 13 +1. 54 i Equation (3) p. 7. Table 3 shows the results by the refractometer method to be con- sistently higher than those by the ether-extract method, due probably to the solution of substances other than oil which affect the refractive index. The close agreement of triplicate results indicates that the refractive-index method of determining the oil content of macadamia nuts is essentially accurate if proper corrections of the curve are made In fact, the differences between determinations are less in most in- stances than those by the ether-extract method. For the present purpose the refractometer method has little to commend it as compared with the specific-gravity method. Ii is much more cumbersome and requires relatively expensive equipmenl Moreover, with the specific-gravity method, the kernels are unaffected so that direct correlation may be had with other characteristics such as chemical composition, roasting qualities, and the like. THE MACADAMLA NUT IX HAWAII 9 RELA I ION OF SPECIFIC GB Wi I V TO TOTAL SUGARS Figure 3 shows the relationship of specific gravity to total sugars iu a series of smooth-shell kernels. There appears to be a definite positive correlation of the two where the percentages of sugar are high and the kernels are obviously immature. 4 The percentage of total sugars in normal, mature kernels varies from about 3 to 5 percent. Within this range there is little correlation. RELATION OF SPECIFIC GRAVITY TO ROASTING QUALITIES If kernels of varying specific gravities are rousted 1 there will be noted a marked relationship bet ween specific gravity and the character .96 .98 £ 1.00 O 1.02 _ 1.04 o 1.06 1.08 o ) i— o o o 4 6 8 10 12 \* TOTAL SUGARS IN KERNEL (PERCENT) Relation of total sugars in inarailanna kernels to specific gravity IG of the roasted product. Kernels of high specific gravity acquire a dark-brov n color, a strong scorched taste, and a, hard or tough con- sistency. At. the other extreme, the low specific-gravity kernels develop a lighl golden color, a, mild nutty flavor, and a crisp texture. Specific gravity may thus be used as a basis for grouping of macadamia nuts according to their adaptability t<> a commercial rousted product. A study whs conducted to determine the relation of various specific- gravity groups of kernels to roasting qualities. Six water solutions were made up of the following specific gravities: 1.100, 1.050, 1.025, 1.000, 0.985, and 0.D70. Sodium chloride was used to make the solu- tions of specific gravity greater than unity while ethyl alcohol was used for the solutions of less than unity. The increments in specific * The terra "mature" is used in this bulletin to mean kernels which are plump in appearance and show- little shrinkage during curing. "Immature" kernels are defined as those which are shriveled and show considerable shrinkage during curing. 5 The term "roasted" is used throughout this bulletin to indicate either oven roasting or oil cooking. Both methods were used. From the standpoint of evaluating kernel quality, the two arc interchangeable. 20846°— 38 2 10 BULLETIN 79, HAWAII EXPERIMENT STATION gravity were made smaller in the solutions less than unity because of the greater concentration of kernels of normal composition in this narrow range. To divide a lot of kernels into specific-gravity groups, the kernels are first placed in the solution of specific gravity 1.000 and stirred vigor- ously to eliminate air bubbles. The kernels which float are skimmed off and the adhering solution removed by centrifuging. They are then placed in the 0.985 solution. Those which sink obviously have a specific gravity between 1 .000-0.985. In a similar manner the other separations are made so that a total of seven groups result from the six solutions, the heaviest group being that which sinks in the 1.100 solution, and the lightest that which floats on the 0.970 solution. Table 4 shows the division into groups by this method and the rela- tion of these groups to roasting qualities. The percentages of oil corresponding to these specific gravities were taken from the values given in figure 1 . Table 4. — Relation of specific gravity of stnooth-shell-typc kernels to roasting qualities Specific gravity Proportion of oil in kernel Appearance of raw kernel Roasting qualities Percent >1. 100 <50 Small size, shriveled base, hard or Very dark color, unpleasant burnt tough texture, off color. flavor, hard texture. 1. 100-1.050 50 -61.5 do Do. 1. 050-1. 025 61. 5-67 do Do. 1. 025-1. 000 67 -72 Slight shriveling of base; variable in Somewhat dark in color, tendency to size and color. off flavors and spongy texture. Sale- able, but distinctly inferior to lighter nuts. 1. 000-0. 985 72 -75 Smooth base, plump, well filled, light Light golden color, mild nutty flavor, color. crisp texture, excellent. 0. 985-0. 970 75 -78.5 do Do. <0. 970 >78.5 do Do. Table 4 shows the best grades of kernels to be those of a specific gravity of 1.000 or less. The group 1.000-1.025 is variable in flavor and texture. Repeated tests of kernels of both types at different seasons of the year and from a number of localities have resulted in the placing of this group in a distinctly lower price class for use possibly in the baking or confectionery trade or as nut butter. Kernels with a specific gravity greater than 1.025 appear to have little value except for vegetable oil or nut butter. There is no perceptible differ- ence in roasting qualities either as to flavor, texture, or color among the groups of specific gravity less than unity. On this basis, all kernels of a specific gravity less than 1.000 arc classed as grade 1; 1.000-1.025 as grade 2; and greater than 1.025 as culls. For practical purposes, it is thus possible to make all necessary separation with two solutions, namely 1.000 and 1.025 (pi. 4). Ordinary tap water at normal room temperature is sufficiently pure for use in commercial grading. This abbreviated method is now be- ing used commercially. It is more rapid and more accurate than hand separation of poor-grade kernels on the basis of the darker color and shriveled appearance after cooking. The expanded grading system is of value in the study of the differences in kernel quality in mils from individual trees. Hawaii Agricultural Experiment Station. Bull. 1^ Plate 4 THE MACADAMIA NUT IN HAWAII 11 The rough-shell kernel conforms fairly well to the same division into grades. However, the differences in texture, color, and flavor between the rough and smooth types persist throughout all specific- gravity grades. QUALITY- RATIO ME1 HOD Of SCORING M ACAD AMI A NUTS General standards have been set up for the grading of the more common commercial nuts. These have to do with the size and appear- ance of the unshelled nut, the relative wholeness of the kernels upon extraction from the shell, the color, size, and plumpness of the kernel, and its condition with respect to insect infestation {3, 8). These standards have been set up largely from the standpoint of market- ing the nut in the unshelled form. The macadamia crop in Hawaii, coming as it does from seedlings, different types, numerous localities, and with great differences in cultural care, is subject to great fluctuation in nut characteristics. There is need for some method of evaluation of these qualities from i lie standpoint of both commercial value and selection. The method of evaluating macadamias as finally developed is designed to determine the pounds of unshelled nuts required to produce 1 pound of grade 1 roasted kernel. This is designated "qual- ity ratio." The following factors enter into this ratio: SIZING OF UNSHELLED NUTS Three screens with round holes 2.75, 2.45, and 2.10 cm in diameter, respectively, are used to divide the unshelled nuts. The four sizes of nuts are thus >2.75 cm, 2.75 to 2.45 cm, 2.45 to 2.10 cm, and <2.10 cm in diameter. All nuts of a diameter >2.1() cm are given full value and are termed sizable while those <2.10 cm are termed culls with no value. This division between sizable nuts and culls is based on commercial practice. Nuts of the cull size are irregular in size, shape, and quality. Discarding of cull nuts likewise serves to eliminate objectionably small sizes of kernels. No further account i< taken of size of nut or of kernel in calculation of quality ratio. PROPORTION OF KERNEL The sizable nuts are cracked and the percent of kernels calculated. GRADING OF KERNELS The kernels of the sizable nuts are graded as in the regular specific- gravity method and the percent of kernels which are grade 1 deter- mined. Grades 2 and 3 are given no value. QUALITY RATIO Calculation of the quality ratio is as follows: Quality ratio = 100 Percent sizable nuts X percent kernel X percent grade 1 kernels An attempt was made to incorporate a color grading into the piality ratio. The normal macadamia kernel has a cream-colored 12 'BULLETIN 79, HAWAII EXPERIMENT STATION base which roasts into an attractive golden brown. Certain kernels apparently due to factors of climate and nutrition, as well as inherit- ance, have off -colored bases in the raw state. Others develop off- colors during roasting. Acceptable color standards for grading have not yet been agreed upon, therefore no account is taken of color in the quality ratio as used in this bulletin. PURCHASE OF NUTS ON THE BASIS OF THEIR QUALITY RATIO The quality ratio gives a single summation value for all the impor- tant qualities which affect the commercial value of the nut. By sub- 23456789 10 QUALITY RATIO (POUNDS OF UNSHELLED NUTS TO PRODUCE I POUND OF GRADE-1 KERNEL) Figure 4.— Quality ratio as a means of determining the gross value of unshelled nuts. The curves repre- sent the selling price of grade 1 kernels. Reading across to the ordinate gives the gross value of the un- shelled nuts at prices of grade 1 kernels from 20 cents to $1 .20 per pound. From this value must be sub- tracted the overhead to find the net value. (Sec below for an example of the use of this graph.) stituting in the formula the values obtained from analyzing a sample of nuts it is possible for the purchaser of a lot of unshelled nuts to calculate the pounds of finished product he may expect. Figure 4 gives the gross value per pound of unshelled nuts of varying quality ratios for prices of the grade 1 kernel varying from 20 cents to $1.20 per pound. An example of the method of using the graph is as follows: Assume that the wholesale price 6 of grade 1 kernels is 80 cents per pound and a given lot of nuts has a quality ratio of 4.5. Reading across to the ordinate from the intersection of the 80 line and $J& '■ These values for price of kernels and for overhead are assumed. The market price and processing costs cannot be climated with any degree of accuracy until production assumes larger proportions and methods Of processing are better developed. The charging of overhead on the basis of unshelled nuts rather than on finished kernels Seems justified in view of the fact that the factory operations of husking, curing, sizing, crack - ing, and grading are the same regardless of t he qualil y rat io. The overhead saving in subsequent dehydra- tion and roasting of the smaller quantities of nuts from the higher quality ratios would be negligible and would be offset by t he enforced idleness of t his part of the factory resulting from the poorer quality. THE Macadam la nut in Hawaii 13 quality ratio gives a gross value of 17.8 cents per pound of unshelled nuts as received. This value can likewise be easily calculated by dividing the price per pound of kernel by the quality ratio; i. e., 80^-4.5=17.8 cents. From this gross value must be subtracted overhead including profit per pound of unshelled nuts, the net being the price per pound to be paid to the grower. Thus with an overhead of 8 cents per pound, 17.8 — 8 = 9.8 cents per pound net. EVALUATING < OMMERCIAL SAMPLES OF MACADAMIA NUTS BY THE QUALITY-R VI [O MKTHOD Two-pound samples of the various lots of macadamias received by a local company were scored by the quality-ratio method. Such samples are composites of all the bearing trees of the orchard in a number of localities and represent sufficiently large quantities of nuts to minimize to a great extent the effect of individual trees. They thus indicate seasonal trends, effect of climate, and average quality which may be expected from the seedling orchards of both smooth- and rough-shell t vpes. s\K »( » i ei-shell rYPl In the appendix (table 14) is given the results of scoring of indi- vidual shipments from five orchards of Bmooth-shel] type, which are the principal bearing orchards of the Territory. Table 5 summarizes these results. In two Locations, Waipahu. and Xutridge, distinct seasonal trends appear. The results are subdivided into periods to make this apparent . 14 BULLETIN 79, HAWAII EXPERIMENT STATION 5 5 "3 2 a C ^ 5 c i- c-i id ed ■<*•' ci »o cc "5 i,' ci cm' "CNN fic J) i-i C _.~oas "5 OS IC i.". ON midi-i S cc cc od s ^ a-, cm as 1 8 c4 ei I 8 ■?7S IS CC5C as cc CM as cc • I — CM CO as -9> oe «d i ~ as ~ CM as CM CM* CM I- CM o oo ih CM 1- CD CO oo "5 as t}> o cc cc CM CC CM CC 00 00 cc ad ci as ih I- cm' rH 00 ,336 275 s CC ^ 00* 2 p Si I-- CM 5 CC i -' »0 CM as as 00 as 2.09 g oo IQ CM r, HAW j N. CM - , MAUI 00 cc" O HAIKU KEAUH 32.7 41.2 CM CM id oc as IC CM as s oo* as p CC O ci •d 1935-J i 4 «d gl cc M 3 4j THE MACADAM I A NUT IN HAWAII 15 The season's average of the various localities shows some marked differences, particularly with regard to the quality of kernels. In this respect Keauhou, Hawaii, is much lower in grade 1 kernels than the others. It is likewise lower in proportion of kernel. In percent of sizing culls and average weight per kernel, all locations are similar and acceptable. At Waipahu, during the initial period the quality of kernels was poor but improved rapidly. The quality ratio reached its lowest value of 3.7") during September and October. In the subsequent period the kernel quality increased slightly but the quality ratio dropped due to a decrease in the proportion of kernel. This phenom- enon lias been noted in other instances and is probably significant. Poor kernel quality during the early part of the season is evident at Nutridge, but there is no appreciable decrease in quality ratio during the last of the season. There is no marked seasonal trend in the grading of the nuts from the other localities although in the case of Haiku, Maui, and Kalaheo, Kauai, the shipments were limited in amount and number, and it is possible that the early harvest of poorer nuts was not sold. W ith roped to Keauhou, however, the harvesting period extended from May 1935 through January 193. Obviously these figures would change with the assumed price and overhead, but they do bring out the important fact that variation in quality is appreciable in commercial samples. An illustration of a single shipment which was below par is Keauhou, sample No. 642 (table 14) with a quality ratio of o.4.~>. This shipment of (*>{)."> pounds on the basis used above was worth only 4.4 cents per pound. New trees coming into bearing, hard winds, drought, excessive cloudy weather, nutritional factors, all may be contributing factors in such a sudden change in quality. Pur- chase of nuts on the basis of their quality ratio would mean a higher price for high-quality nuts and should act as a stimulus to growers to improve quality through top working and better cultural practices. BOUGH-SHELL I IPE Samples of rough-shell nuts were received from the Macadamia Nut Cooperative Marketing Association, located at Kailua, Hawaii. The association hand-cracked the crop and divided the kernels by specific gravity into grades. Composite samples of the hand-cracked kernels of each shipment were forwarded to the station. .Results of scoring these commercial shipments are given in table 6. BULLETIN 79, HAWAII EXPERIMENT STATION Table 6. — Scoring of factory shipments of rough-shell-type macadamia nuts from Kona, Hawaii, 1935-36 Shipment No. Date received at Honolulu Weight of un- shelled nuts Propor- tion of kernel Percentage of kernels having a grade and specific gravity of— Quality ratio Grade 1 kernels Grade 1 « 1.000) Grade 2 (1.000- 1.025) Grade 3 (> 1.025) 1 2 Dec. 1935 Feb. 17,1936 Mar. 7,1936 Mar. 17, 1936 Mar. 26, 1936 May 7, 1936 May 25, 1936 Pounds 136 ~"~295~ 808 1,228 695 418 Percent 21.7 24.0 26.4 25.5 24.6 23.5 27.0 Percent 27.9 44.5 53.4 70.8 65.5 79.9 84.9 Percent 38.2 40. 1 33.7 23.5 23.9 16.2 12.7 Percent 33.9 15.4 12.9 5.7 10.6 3.9 2.4 16. 54 9. 35 7. 09 5. 54 6. 22 5. 32 4.35 Pounds 8.2 3 4 5 6 7 41.7 146. 1 197.4 130.6 97.0 Table 6 shows an extremely poor quality of kernels in the early part of the season, with only 27.9 percent grade 1. Improvement in quality is rapid as the season advances, the last shipment having the highest value of 84.9 percent. The bulk of the crop was contained in the fourth, fifth, and sixth shipments, in which the proportion of grade 1 kernels was 65.5 to 79.9 percent. This is much below the standard of the smooth-shell types. As has been noted, the rough- shell type has other undesirable features as a commercial nut, such as poor color, variable flavor, and undesirable tree characteristics. EVALUATION OF NUTS FROM DIFFERENT SEEDLING TREES FROM DIFFERENT LOCALITIES The bearing trees of macadamia are made up of miscellaneous old trees found in many locations throughout the Territory and a number of commercial orchards, many of which are just coming into bearing. All trees are seedlings. The origin of the seed used in the various plantings is seldom known even in the younger commercial orchards. It requires only casual inspection to note the great variations among the trees in any one orchard. These variations are manifest not only in vegetative characteristics but also in fruiting habits, such as total yields, distribution of the harvest throughout the year, and the various factors of nut quality. VARIABLE FACTORS DISTRIBUTION OF THE CROP THROUGHOUT THE BEARING SEASON Nuts were collected throughout the bearing season from a series of 12 seedling trees at Waipahu, Oahu, to determine the variations in the drop of nuts throughout the year. The results are given in table 7. THE MACADAMIA NUT [N HAWAII 17 Table 7. — Variations in distribution of the crop of husked nuts throughout the bearing season of 12 8-year-old seedling trees of the smooth-shell type, Waipahu, Oahu, 1930-31 crop Tin No. uao 1931 Total yield July Ail};. Sept Oct. Nov. I tea Jan. Feb. Mar. A | >r. l 3-""""""""""""" u>. 17.9 .4 3.6 5.3 Lb. 10.8 1. 1 17.0 6.6 .3 2.2 1.2 .3 2.6 17. 1 6.4 6 7 Lb. 23.7 8.9 12.8 lo. 9 1.0 13.5 5.8 2.9 113 14.5 25 7 12 9 Lb. 6.5 8.3 12. 11.5 5.3 11.0 16.0 31. 5 12.8 11.5 10. 5 .6 Lb. 1.3 5.5 2.8 10. 1 7 4 9.5 4.3 5.6 4.8 6.3 1 I Lb. 0. 7 6.2 2.8 5.2 17.8 1.6 5.6 8.9 2.7 4 2 Lb. 0. 4 9.8 2.8 4 1 6.4 1.3 8.3 3.5 1.0 1.7 Lb. 1.0 3.9 2.0 1. 1 1.8 .7 6.3 4 3 .4 Lb. 1.3 2.3 1.6 1. 1 3. 1 1 4 3.8 4.5 Lb. 0.9 1.0 Lb. 0.6 .7 Lb. 65.1 48. 1 57.4 55 9 43^ 1 43.8 53.5 66.6 36.2 54.6 52. 1 47 4 5 2.6 .3 .6 .6 3 1 8.2 22 \> 8.. 9 1.3 3.8 .6 .7 10 u 12 3 1 | .6 .8 In this group of trees there are early hearers (N'os. 1 and 12) and late bearers (No. 5). There are those which bear the hulk of their crop in 2 or 3 months (\o. II) jind others which bear nearly the year around (Nos. 7 and 8). The variation in bearing habits of the noacadamia gives a wide range of harvest possibilities which commer- cialized interests may use to base further plantings of selected trees tr conform, in turn, with local Labor and processing conditions. TYPES OF niSTKIBl'TlON OF KKKNKI.S INTO SPKCIFIC-OKA YITY OKADES Grading of many lots of macadamia nuts taken systematically from specific locations or individual trees has shown different and characteristic types of distribution. Table S shows typical examples. Table 8. — Characteristic types of distribution into specific-gravity grades of nuts fnun stalling trees IVreetitagr of nuts in the group haying u specific gravity of— 1 )istrilmtion I ype ;m 1.050) Smooth shell : Percent Percent Percent Percent Percent Percent a 11 58 l b' a 25 18 18 10 16 c •23 39 31 1 6 d 20 21 18 I 40 Rough shell: e 16 37 22 21 3 1 f.. 3 6 20 20 51 Same tree as "a" the following year. In considering table 8, it is not possible to separate out and evaluate the various factors of type, locality, condition of tree, size of crop, and the like which might affect grade of kernels. The differences in specific-gravity distribution between crops from the same tree in successive years are illustrated in types a and b. In 1930-31, type a, the yield was heavy and practically the entire crop was in groups 1 and 2. In 1931-32, type b, the crop was distributed fairly evenly through all groups, only 56 percent being grade 1 kernels (groups 1 18 BULLETIN 79. HAWAII EXPERIMENT STATION to 3, inclusive). Type c is typical of a good smooth-shell tree, a large proportion of the nuts being grade 1. What poor nuts there are tend to be in group 6. Type d represents an extreme example of this tendency. This phenomenon might be ascribed to inherited characteristics or to early nutritional disturbances which later dis- appear since the distribution in the other groups is normal. Type e is a typical distribution for the rough-shell type. Whereas the smooth-shell type normally has few nuts in grade 2 (group 4), the rough-shell usually has a considerable percentage. This tendency to underfilling appears to be a characteristic of the rough-shell type rather than the result of nutritional disturbances. Type f shows how extreme this tendency may become with the rough-shell type. SEASONAL CHANGES IN DISTRIBUTION It has been previously noted that the crop varies in quality through- out the season, the first nuts which drop usually being poor in quality. If the tree is normal and in good condition, this represents only a small fraction of the crop. Sometimes this poor quality continues throughout the season. In table 9, tree No. 4 illustrates the rapid improvement in quality during the season, the bulk of the crop being borne during the last 3 months. With tree No. 10 the crop remained poor in quality throughout the season. This underfilling caused a marked decrease in the average weight per kernel and in proportion of kernel from that of the previous season. Table 9. — Seasonal changes in distribution in specific-gravity groups, smooth- shell type, Waipahu, Oahu Percentage of kernels having a grade and specific gravity of— Tree and month of harvest Proportion of kernel Average weight per kernel Grade 1 Grades 2 and 3 <0.970 0. 970- 0.985 0. 985- 1.000 > 1.000 Tree No. 4: 1930 average ... ... Percent 28.5 Grams 1.87 Percent 13 Percent 70 Percent 12 Percent 4 1931 June... 27. 6 1.34 1 fe! 20 79 July 27.4 1.45 1 9 26 64 August 27.3 26.9 1.63 1 52 23 24 September. . 1.74 14 fi4 12 10 October 27.7 1.86 24 70 6 November. 27.6 1.77 20 80 Tree No. 10: 1930 average 40.7 1.91 41 58 1 1931 July.. 36.8 1.45 6 52 14 28 August. 35.7 1.28 2 28 26 44 September.. 35. 9 1.37 7 25 23 45 October 36.5 1.37 13 25 18 44 November 37.5 1.44 20 21 18 41 December 37. 1 1.39 19 27 16 38 YIELD AND NUT QUALITY OP SEEDLING TREES FROM DIFFERENT LOCATIONS Study lias been made over a period of years of representative trees from a number of the commercial orchards for the purpose of deter- Hawaii Agricultural Exp*rimrnt Station. Bull. 79 Plate 5 Va riations in Size and shape of leaves from smooth -Shell Seedling Trees in a Single Grove. Hawaii Agricultural Experiment Station, Bull. 79 PLATE 6 A 12-Year-Old Seedling macadamia Tree, Smooth-Shell Type. Seedling trees vary greatly in shape. This demonstrates an open tree with slender branches. THE M V.CADAM1 \ NUT !\ B \ W MI 19 mining t ho extent of variation among seedling trees and the adapta- bility of the macadamia, to various localities in Hawaii (pis. 5 and 6). Certain changes were made in methods used during the progress of the project. Differences in facilities available at the different locations have likewise affected the type of data which could be collected. The data on the individual trees are, therefore, not the same for the different localities. On Oahu it has been possible to get monthly samples and individual tree yields. At the other locations the data arc le-s complete. No individual tree yields could be had and the samples usually consisted of but one or two taken during the peak of the crop. Tables 10 to 12 summarize the study of individual trees From Wai- pahu and Nut ridge on Oahu, Kona and Kohala on Hawaii. NUTRIDGB Complete records were kept of t ho monthly yield and nut quality on eight trees at Nutridge over a X-year period. The trees were planted at varying times, the average age being about 10 years. These trees were selected on the basis of some desirable quality such as yield or percentage kernel and hence do not represent a cross section of the orchard. This grove is at an altitude of 600 to 800 feet and has moderate rainfall. Table 10 shows that in all cases the season's average percentage of grade 1 kernels is very high, in all but three cases it is more than 00 percent. One tree, C 8 ">4, would be rated as commercially undesir- able because of the large percentage of sizing culls in spite of good quality in other respects. The Beasonal effect is apparent in C-14-156 where the size dropped badly in the 1935-36 harvest. Table 10. — Yield and nut characteristics of 8 sv>ooth-shcll-(>/pc seedling trees for 3 years, Nutridge, Oahu Tree No. Year Samples tested Propor- tion of un.shelled nuts >2.10 cm in diam- eter Propor- tion of kernel Propor- tion of kernels of prade 1 guality ratio Yield of un- shelled nuts per year Yield of grade 1 kernels per year Xiimhrr Percent Percent Percent Pounds Pound* 1 1933-34 95 30 88 4.05 51 12.6 A-i2-73 { 1934-35 9 100 29 93 3. 70 65 17.6 1 1935-36 100 29 92 3.81 69 18. 1 I 1933-34 2 98 32 98 3. 07 75 24.5 A 13-83 { 1934-35 95 37 100 2.85 79 27.7 1 1035-30 2 80 39 96 3. 24 119 36.8 1 1938-34 6 74 40 92 3. 72 48 12.9 C-8-54 \ UNM-36 3 48 34 97 6.32 22 3.5 I 1935-36 1 23 3fi 98 12.42 1933-34 8 95 28 97 3. 93 44 11.2 C-8-57 \ 1934-35 100 26 97 3.96 53 13.4 I 1935-36 5 98 28 97 3. 77 42 IL 1 1 1933-34 8 97 29 87 4.07 33 8. 1 O-10-89. \ 1934-35 5 99 31 99 3. 28 38 11.6 I 1935-36 1 83 33 93 3. 87 | 1933-34 5 99 31 98 3. 30 41 C-14-154 < 1934-35 5 92 98 30 97 3. 73 3.83 60 [ 1935-36 1 31 85 96 | 1933-34 5 85 39 3. 17 44 13.9 C-14-156 \ 1934-35 7 88 35 99 3. 29 37 11.2 ( 1935-36 6 43 36 92 7. 02 47 6.7 1 1933-34 8 94 32 96 3. 48 46 13.2 C-2S-415 { 1934-35 8 96 33 95 3. 32 57 17.2 t 1935-36 7 83 34 98 3.60 65 18.0 20 BULLETIN 79, HAWAII EXPERIMENT STATION WAIPAHU, OAHU Twelve trees were selected at random to determine the extent of variation in the Waipahu orchard. The orchard was about 8 years old. The location is at sea level and dry, the trees being irrigated when necessary. Each result is the average of five to seven samples taken throughout the bearing season. These trees are the same as in table 7. The results are given in table 11. Table 11. — Yield and nut characteristics of 12 smooth-shell-type seedling trees at Waipahu, Oahu, 1930-31 crop Tree No. 1 Total yield of un- shelled nuts Propor- tion of kernel Aver- age weight per kernel Percentage of kernels having a grade and specific gravity of— Quality ratio Yield of grade 1 ker- nels 1 Grade 1 Grades 2 and 3 <0.970 0. 970- 0.985 0.985- 1.000 Total grade >1.000 Pounds Percent Grams Percent Percent Percent Percent Percent Pounds 1 65. 1 32. 4 2. 02 9 61 21 91 9 3. 42 19. 1 2 48. 1 33. 3 1. 72 14 63 14 91 9 3. 33 14.5 3 57.4 31. 5 2. 02 8 84 ■ 7 98 2 3. 24 17. 7 4 55.9 28. 5 1.87 13 71 14 96 4 3. 65 15.3 5..... 43. 1 22. 9 1. 85 8 58 29 94 6 4. 64 9.3 6 43.8 28. 5 1. 87 2 62 27 90 10 3.91 11.2 7 53. 5 24. 3 2. 00 9 67 17 93 4. 38 12. 2 8 66. 6 28.8 2. 24 13 79 5 97 3 3. 58 18.6 9 36. 2 20.9 2. 41 6 58 24 88 12 5. 43 6.7 10 54. 6 40. 7 1. 91 41 58 99 1 2. 48 22.0 11 52. 1 31.8 2. 23 20 67 8 96 4 3.28 15.9 12 47.6 30. 1 1.86 21 64 12 96 4 3. 46 13.8 1 Same trees as in table 7. 2 Total yield of unshelled nuts divided by quality ratio. No sizing of unshelled nuts was done during this time. As noted in table 1 1 the proportion of kernels which are grade 1 is uniformly high. All trees but one bore 90 percent or more of grade 1 kernels. The variation in proportion of kernel is from 20.9 to 40.7 percent. The variation in yield of grade 1 kernels per tree of from 6.7 to 22 pounds is indicative of the possibilities for improvement of an orchard through elimination or top working of undesirable trees. KOHALA, HAWAII The trees in the Kohala orchard were 8 to 12 years old at the time of this test. The elevation is 400 feet above sea level and the rainfall about 40 inches. Only one sample was taken from each tree during the period of greatest nut drop. Results are given in table 12. THE MACADAM LA NUT IN HAW A I I 21 Table 12. NtU characteristics of 10 smooth -shell-type seedling trees at Kohohi, Hawaii, 1933-34 harvest tionof Average weight per kernel Percentage of kernels having a grade and specific gravity of— Tree No. un^helled >J. 10 cm p tion of kernel Grade 1 (lr;i<1p 9 Quality ratio in H i n m - eter < 0.985 0.US5 1.000 1.000- 1.025 ^> 1 .025 Percent 92 Pi TCi lit 32. 3 Gram* 2.or> Percent 9 Percent 7 Peroral Percent 3 3.47 100 27.3 2.29 95 4 1 3. 94 i 100 28. 2 2.57 96 4 3. 70 4 90 24. 9 2.73 86 f» 8 5.58 6 100 33. 3. 07 98 2 3.09 6 100 31.8 2. '■><) 100 3. 15 7 94 30.9 2. 38 86 4.05 8 100 31.3 2 18 84 10 3.99 9 100 18.3 2.51 83 6 11 fi. 58 10 100 35. 7 2. 18 VI 2 «.i 3. 15 All tiers are acceptable us to size of nut with a somewhat higher average weight per kernel than found in other orchards. The pro- portion of grade 1 kernels is also good. 'Frees f> and (> are exceptional in that they have unusually large kernels, 100-percent sizable nuts, and at the same time a relatively high percentage of kernels. This, together with very high proportion of grade 1 kernels, results in tin 1 low quality ratios of 3.00 and 3.15. CORK ELATION <>1 Ql VLI'IA <>t KKKNKL. WKMiHT OF I N SHELLED NUT AND KERNEL \m> PERCENT OF KERNEL A statistical examination was made 4 of the data secured from nuts of individual trees of the smooth-shell type grown at Xutridge, Oahu (table 10), to determine the correlation between the different nut characteristics. The results given in table 13 are based on 139 indi- vidual samples of nuts. Table 13. Correlation of quality of kernel, neigh t of ufisfieued nut and kernel, and percent ktrm I Variables Coefficient of correla- tion (r) Quality of kernel I Do Do Weight of unshelled nut . Do Percent of kernel Weigh! of unshelled nut Weight of kernel Percent of kernel Weight of kernel Percent of kernel Weight of kernel -0.02 +.02 +. 18 +.68 -.58 .01 > Percent of kernels which are grade 1 (i. e., with a specific gravity less than unity). From table 13 it may be concluded that (1) quality cannot be improved by selection for weight of nut or of kernel or of percent kernel; and (2) weight of kernel can be increased by selection for weight of nut but in so doing the percent of kernel drops off. DISCUSSION Investigations by the Hawaii Experiment Station show the great variation in nut characteristics among the several thousand bearing macadamia seedlings throughout the Territory. Within a single or- chard of the same type, the percent kernel may vary from 20 to 40 22 BULLETIN 79, HAWAII PLXPERIMENT STATION and the percent of grade 1 kernels (specific gravity less than 1) from 6 to 100. This percentage likewise may vary between wide limits for the same tree throughout the year as does the average value from one year to the next. Samples from commercial shipments of nuts received at the factory from different orchards obviously show less fluctuation than those from individual trees. The variations are sufficiently great, however, to warrant their being taken into account in the purchase of the nuts. For example, the quality ratio of the crop from one location was 5.70 during July and August, 3.75 during September and October, and 4.22 for the remainder of the crop. Since quality ratio represents the pounds of nuts in the shell as received to produce 1 pound of grade 1 kernels, these differences are of vital importance, the nuts of 3.75 quality ratio having a value approximately double those of 5.70. Correspondingly greater differences result when nuts are purchased from different localities. It would seem sound commercial practice that some account be taken of these differences in quality ratio in fixing the purchase price for nuts harvested from seedling trees from different localities. The fact that the composite crop from an orchard of bearing trees shows a small fluctuation in quality ratio compared with individual seedling trees is of course no argument for seedling trees. It simply means that the high-quality trees neutralize the low-quality, the upper limit being determined by the relative proportion of desirable and undesirable trees present. The records on individual trees are of value chiefly in showing the nature and extent of variation in nut characters, comprising as they do representative trees from the principal orchards of the Territory. The study likewise has served to develop the tecnhique necessary in evaluating the nut characteristics. It has shown that records of nut quality should be made on a tree over more than one crop and during the entire bearing season if possible. If this is not possible, the samples should be taken during the peak of the nut drop over several seasons. The differences between nuts from different localities were obviously the resultant of such factors as origin of seed, climate, culture, and the like. There are same indications that location affects kernel quality both as to percentage of grade 1 kernels, and the color of the kernel and the epidermis of the basal portion. From the standpoint of nut quality the best locations appear to be the relatively dry, leeward sides of the islands. The results given herein would seem to show an inherent difference in nut qualities between the smooth-shell and rough-shell types of nuts. Horticulturally, the two types are distinct. They produce two dif- ferent curves when specific gravities of kernels are plotted against the corresponding percentages of oil. The flavor, texture, and roasting qualities are likewise different. The rough-shell type appears more prone to underfilling of kernels and appears to show greater variability in this respect than the smooth-shell type. Public preference is gener- ally for the smooth-shell type because of its mild flavor and crisp tender texture, although many prefer the more pronounced, sweeter flavor and firmer texture of the rough-shell type. The present com- mercial demand is almost entirely for the smooth-shell type and THE M M A I > AM I A NUT IN HAWAII 23 indications are that most of the roucrh-shell trees will be either elimi- nated or top worked. The methods used in this study were devised primarily to evaluate the macadamia as a shelled processed kernel. As finally adopted, a sample is carried through the process of sizing the unshelled nut to eliminate small sizes, shelling, and specific-gravity grading to elimi- nate kernels of poor quality. The resultant quality ratio gives as a single value the pounds of nuts as received to produce 1 pound of grade 1 kernel As such, the method has proved useful both in the experimental phases and as a commercial procedure. SUMMARY This bulletin reports investigations by the Hawaii Agricultural Experiment Station on development of methods for evaluating the macadamia nut from the standpoint, of a shelled roasted product, and application of these methods to tin 4 evaluation of nuts from com- mercial orchards throughout the Territory. It was found that the specific gravity of the macadamia kernel has a very high negative correlation with the percent oil ( — 0.985 for the rough-shell type and —0.979 for the smooth-shell type). The method thus serves as a rapid method for determining the oil content. Specific gravity is likew ise related to the roasting quality of maca- damia kernels. It has been found that kernels may be graded as to roasting qualities as follows: Grade 1 specific gravity less than 1, grade 2 — specific gravity between 1.000 and 1 .02"), and grade 3— - specific gravity greater than 1.025. Only grade 1 kernels are used in present commercial packs. A single value known as quality ratio was developed which desig- nates the pounds of unshelled nuts as received to produce 1 pound of grade 1 kernels. Individual seedling trees show great variation in nut characteris- tics, the large number of bearing trees furnishes ample material for selection as to size, percent kernel, and quality of kernel, as well as total yield. There is evidence of significant difference in kernel characteristics between the rough-shell and smooth-shell types of macadamia nuts. The latter is the better type as judged by kernel quality and adapta- tion to the roasted pack. ( Commercial shipments of unshelled nuts received at the factory show- marked difference in quality ratio. It is believed that the purchase price of the nuts should be based on the quality ratio. LITERATI RE ( ITED (1) Camp, A. P. 11930). avocado maturity studies. Fla. Agr. Expt. Sta. Rept. 1929-30: 79-81. (2) Coleman, I). A., and Fellows, H. C. 1927. oil content of flaxseed, with comparisons of tests for de- termining oil content. U. S. Dept. Agr. Bull. 1471, 35 pp., illus. (3) Drake, N. F. 1930. a method for grading black w alnuts. Ainer. Nut Jour. 32 (2): 28. (4) Foth, G. 1907. DIE BEST1MMUNG DES STARKE GEHALTES DER KARTOFFELN NACH DEM -ikzifischen gewicht. Ztschr. Spiritusindus. [Berlin] 30: 217-218. [Abstract by J. F. B. in Jour. Soc. Chem. Indus. 26: 705. 19071 24 BULLETIN 70, HAWAII EXPERIMENT STATION (5) Lewis, R. D. 1932. DETERMINATION OF OIL CONTENT OF PECANS. NEW SULFURIC ACID digestion method. Indus, and Engin. Chem., Analyt. Ed. 4: 296-297. (6) Nichols, P. F., and Reed, H. M. 1932. RELATION OF SPECIFIC GRAVITY TO THE QUALITY OF DRIED PRUNES. Hilgardia 6: 561-583, illus. (7) Pope, W. T. 1929. the macadamia nut in Hawaii. Hawaii Agr. Expt. Sta. Bull. 59, 23 p., illus. (8) Shuhart, D. V. 1932. ENDOSPERM AND EMBRYO DEVELOPMENT AS RELATED TO FILLING OF pecans and walnuts. Amer. Soc. Hort Sci. Proc. (1931) 28: 161-163, illus. APPENDIX There is appended table 14 that shows seasonal variation in nut quality of commereial shipments of macadamia nuts from different bearing orchards iii Hawaii. Table 14. — Scoring of factor// shipments of smooth-shell-type nuts from different In aring orchards, 1935-36 WAIPAHU. OAHU Entry No. soy 22 229 381 388 Date re- ceived MM July 26 Aug. y aul' la Ann. 33 Beg*. | Subtotal or aver- age Sept IS Sept. 30 Sept. 37 Oct. 4 Oct. 11 Oct. 88 Subtotal or aver- age 29.1 801 388 :m 44. r . us 649 817 Kl.s S19 8 20 I >cc ...do... Dec. 13 Dec. 20 •Dec. 27 im Jan. 3 Jan ID Ian. i: Jan. 24 Subtotal or aver- age Season total nr average 821 bss Weight of nuts re- Mtved Lb. 146 98 108 200 IM 736 29* 2M 800 i-,.', Ml LOOS 546 273 :,»,* MS 3.82 300 3M 8, 004 5. 6,s5 Sizing (diameter) of onflheDed nuts Larue, >2.75 cm y,/. 4 2 6 3 4 3 9 8. 7 8.2 5.8 Medi- um, 2.75- 2 4.1 en Small. 2.45- 2.10 cm Pet : 5 82 4 29 (I IN .I 29. 1 _N II 29.3 27.0 25.3 27.3 24. 1 26. .1 26. 26. 1 26.3 27. 1 26. 2 27 7 Aver- age weight ner kernel drum* 1.70 1.99 2.01 1.96 2. 11 95 I is 2. 07 2.00 2. 04 2. .19 2. 16 2. 17 2. 17 2 U7 1.94 1 S2 2.09 2.03 2. 05 2. 08 2. 00 Percentage of kernels having a grade ami specific gravity of Grade 1, < 1.000 I'd. 50.8 67 2 68 H 86 II Mi .1 71 B 94. 1 9.1.2 92 7 96.3 100 9.1. 7 95. 6 88. 5 96.0 88 a 98. 1 99.5 95.3 98.0 9.1.4 92. 2 2. 02 96 3 2. 10 90. 00 » Irade 2, 1.000- 1.025 Pet. 26. 9 19. 4 19. 6 10. 2 9. 2 17.0 5.3 2.2 4.4 1.7 3.5 2 9 4.0 3.8 1.3 1. 1 0.5 2. 1 1.2 2.0 5.8 2.4 6.2 NUTRIDQE, o.Ull 19S5 Lb. Pet. Pet. Pet. Pet. Pet. (Ira BU Pet. Pet. Pet. 205 July 2 231 5 35 .16 4 28.8 1.95 73.7 22.4 4.0 4.90 207 July 12 321 5 26 60 9 SB. 5 1.96 74. 5 15. 7 9.8 5. 18 222 July 27 336 90 10 25.7 2. 87 62.8 22. 1 15.2 6. 17 224 Aug. a 2.16 1 23 60 16 30.7 2. 07 83.4 10.3 6,3 4. 65 226 Aug. 10 425 8 22 57 13 28. 1 2.00 83.0 7.0 9. 7 4.94 230 Aug. 17 422 3 26 58 12 31.3 2. 10 80. 1 13.9 6.0 4. 58 232 Aug. 20 143 100 33.0 1.87 89.9 3.2 6.9 3. 37 233 Aug. 27 426 5 31 56 8 29.8 2.00 80.3 7.8 11.9 4.51 234 Sept. 3 776 8 42 4,3 31.6 2. 19 82. 1 12.4 5.5 4. 10 Subtota ' or aver- age 3.336 13.8 23.9 54.5 7.8 29.7 2. 11 78.9 12.7 8.4 4. 71 294 Sept. 10 866 5 33 56 6 30. 1 2. 16 94.0 3.4 2.6 3. 78 296 Sept. 14 124 100 31.8 1.89 90. 5 7.0 2.5 3. 45 297 Sept. 17 77.1 5 43 48 4 30.6 2. 23 84. 7 10.4 4.9 3. 97 387 Sept. 24 739 6 38 50 5 29.3 2.23 87.6 9. 1 3.4 4.15 390 Sept. 30 691 4 30 60 6 32. 1 2.25 96.3 3.4 .3 3.46 447_ Oct. 7 1,210 6 42 46 6 30.3 2. 36 92.5 4. 5 2.9 3. 83 450 Oct. 14 I, 210 i 37 49 8 31.0 2. 27 94.4 4. 7 1.0 3. 70 453. Oct. 21 1,258 5 45 45 5 29.6 2. 25 94.3 2.4 3.3 3. 73 456 Oct. 28 1.154 5 50 41 4 30.4 2. 24 96.0 2.2 1.8 3. 61 644 Nov. 26 I, 147 25 28 43 4 27.3 2. 21 99. 1 .8 3 90 646 Dec. 2 997 12 47 27 13 26.6 2. 06 97.8 1.4 .8 4. 36 648.... Dec. 9 589 9 39 46 6 29.8 2. 22 95. 6 4. 1 .3 3.71 812 13 40 37 10 29.4 2.29 97.3 2.2 .5 3. 89 1 Pounds of unshelled nuts required to produce 1 pound of grade 1 kernels. 25 2g BULLETIN 79, HAWAII EXPERIMENT STATION Table 14. — Scoring of factory shipments of smooth-shell-type nuts from different bearing orchards, 1935-36 — Continued NUTRIDGE, OAHU— Continued Entry No. Date re- ceived 1935 Pec. if! Dec. 23 Dec. 30 1936 Jan. 6 Jan. 13 Jan. 20 ...do Jan. 27 Subtotal or aver- age Season total or average Weight of nuts re- ceived Lb. 1,242 485 690 814 427 428 15, 275 18,611 Sizing (diameter) of unshelled nuts Large, >2.75 Pet. 11 9 Medi- um, 2.75- 2.45 cm Pet. 41 2 33 38 37 41 37 32.0 Small, 2.45- 2.10 cm Pet. 52. 1 51.8 Culls, <2.10 cm Pet. 5 11 7 3 6 7 5 7 6. 1 Pro- por- tion of kernel Pet. 29. 9 34. 9 28.5 29.9 28.7 31.0 31. 1 31.2 30.2 30.0 Aver- age weight per kernel Grams 2. 37 • 1.81 2. 48 1.83 2. 26 2. 48 2.39 2. 19 2. 21 2. 19 Percentage of kernels having a grade and specific gravity of— Grade 1, < 1.000 Pet. 98.8 95.3 100.0 97.4 97.6 97.6 97.7 98. 2 95. 4 Grade 2, 1.000- 1.025 Pet. 4. 7 2. 1 1.3 1. 2 2.3 3.2 6.0 KEAUHOU, HAWAII 1935 May 15 June 28 Aug. 2 Aug. 13 Sept. 3 Aug. 23 Sept. 9 Sept. 20 Sept. 24 Oct. 3 Oct. 11 Oct. 18 Oct. 25 Nov. 15 Nov. 29 Dec. 12 1936 Jan. 10 Jan. 30 Season total or average. - Lbs. Pet. Pet. Pet. Pet. Pet. Grams Pet. Pet. Pet. 8 52 36 4 24.2 1.95 69. 2 21.8 9.0 278 8 42 48 2 25.4 1.95 74.3 12.4 13.3 529 94 6 24.4 2.91 73.3 17.2 9. 5 380 4 59 34 3 26. 1 2. 02 63.7 16.7 7.5 647 6 58 33 3 27.8 2. 20 85.5 10.0 4.4 408 18 48 31 3 23.7 2. 09 80.4 13.9 5.7 380 15 49 34 1 25.0 2.04 84.6 7.5 7.9 795 15 47 39 26.0 2. 12 86.4 6.4 7.2 739 11 37 45 6 25.3 1.98 82.3 12.8 5.0 485 25 52 23 1 26. 1 2. 26 78.0 17. 1 5.0 517 8 38 49 5 24.7 1.85 80. 1 13.5 6. 4 611 12 48 38 2 25.0 2. 04 79. 2 13.2 7.6 567 13 43 41 3 25.6 1.65 79. 2 14.3 6.6 695 23 37 26 13 34. 2 1.93 52.4 27.6 20.0 475 20 58 22 27.0 2. 25 86. 2 11. 1 2.7 417 24 50 26 25. 1 2. 16 88.8 6.8 4.5 716 25 48 27 24.3 2. 12 84.6 10.9 4.5 336 20 41 36 3 25.9 2. 16 89.3 6.4 4.3 8, 975 19.4 45. 2 32.7 2.7 25.8 2.09 78.9 13. 5 7.6 HAIKU, MAUI 227 1935 Aug. 13 Oct. 2 Lbs. 55 Pet. 6 I'd. 36 Pet. 55 Pet. 3 Pet. 30. 2 Grams 1.97 Pet. 86. 5 Pet. 4.2 Pet. 9.4 3. 97 392 221 12 36 47 5 27.5 2. 02 90.3 7. 1 2.6 4. 32 457 Oct. 29 343 6 39 50 5 29. 1 2. 12 94.7 3. 2.3 3. 83 641 Nov. 15 212 7 50 40 3 27.7 2. 14 94. 6 2. 1 3.3 3. 90 643 Nov. 23 139 269 11 48 38 3 28.3 2. 00 97.4 1.0 1.5 3. 78 647 Dec. 5 23 46 30 1 27. 2. 09 99. 5 .5 3. 76 826 13 44 37 5 26.9 2. 44 97.0 .7 2. 2 4. 03 827 Dec. 24 373 8 54 33 5 29.4 2.05 99. 1 .9 3.61 Season total or average. 1,612 10. 8 44. 2 41. 2 3.8 28.6 2. 23 94.9 2.4 2.7 3. 00 KALAHEO, KAUAI 1935 Lbs. Pet. Pet. Pet. Pet. Pet. drums Pet. Pet. Pet. 4. 3H 394 Oct. 7 932 28 10 2H. 1.91 90.7 6. 3 2.9 828 Dec. 23 615 23 22 45 11 35. 3 2. 15 95. H 2. 7 1. 5 3. 33 1936 4. 51 120 Jan. 27 147 17 36 42 25. 1 1.97 93. 2 5 5 1.3 Season lotiil or average. 1,69 J 15. 28.7 4*. 3 8.7 29. 5 2. 01 93. 3 4.8 1.9 4.07 U.S. OOVt. HNMtNT PHINTINO OFFICES l»fl UNIVERSITY OF FLORIDA 3 1262 08929 0752