UNITED STATES DEPARTMENT OF AGRICULTURE

DEPARTMENT BULLETIN No. 1420

Washington, D. C.

August, 1926

RELATION OF KERNEL TEXTURE TO THE PHYSICAL CHARACTERISTICS, MILLING AND BAKING QUALITIES, AND CHEMICAL COMPOSITION OF WHEAT

BY J. H. SHOLlenberger, Milling Investigations, and D. A. COLEMAN, Chemical Research Laboratory, Grain Division, Bureau of Agricultural Economics

Wheats of certain classes containing a high percentage of hard and vitreous kernels usually command a premium over the price paid for the yellower or more starchy appearing wheats of the same class. The reason is that the hard vitreous kernels are more glutenous and are generally believed to have superior bread-making qualities. This belief has existed in the minds of the grain trade for many years, and because of it when the official United States grain standards were promulgated, the percentage of hard and vitreous kernels present was taken as the basis for establishing subclasses for the hard red spring, hard red winter, durum, and white wheat classes.

In the official grade requirements for the hard red spring and hard red winter wheat subclasses, these kernels are referred to as "dark, hard, and vitreous"; for the durum wheat subclasses as "hard and vitreous kernels of amber color"; and for the white wheat subclasses as "hard (not soft and chalky)".

SOURCE AND DESCRIPTION OF SAMPLES USED

To establish definitely whether a relationship exists between kernel texture and milling and baking quality, the following special studies on the hard red spring, hard red winter, and durum classes were made.

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With the aid of certain of the Federal grain supervision offices of the Bureau of Agricultural Economics and the Office of Cereal Investigations of the Bureau of Plant Industry, three special samples each of hard red winter and hard red spring and two of durum wheat were obtained and from a portion of each of these there were separated, by hand picking, a sufficient quantity for milling, baking, and chemical tests of kernels of the three following types of texture: (1) Dark, hard, and vitreous, or amber; (2) spotted or mottled; and (3) yellow or starchy. Considerable care was taken to make these separations as distinct and consistent as possible; that is, the kernels selected as dark, hard, and vitreous, or as hard and vitreous and of amber color were practically 100 per cent free from starchy specks or spots. For the sake of convenience this type of kernel texture hereafter will be referred to as "dark." The yellow or starchy kernels varied from seven-eighths starchy to all starchy in appearance. The spotted or mottled kernels included the in-between range of starchiness, from a mere speck up to seven-eighths, and for that reason varied more widely in appearance than did the kernels of the other two separations.

The separations of kernels of dark type of texture made in connection with this experiment corresponded with the separations which are made in the grading or inspection of wheat for marketing purposes, except that the latter usually include the slightly mottled kernels.

Three of the samples selected represented commercially-grown wheat, and five were true varietal wheats grown at agricultural experiment stations. In procuring the commercial samples, care was taken to insure against their being mixtures of wheats from different sections of the country. The true varietal samples were selected in order that, on at least a portion of the experiment, there would be positive assurance that any differences shown in results would not be due to differences in variety, climate, soil, or cultural conditions. Furthermore, for the sake of convenience in separating, each selection was of bright clean wheat containing approximately equal proportions of these three different textures of kernels. There was one exception in the case of the hard red winter wheat sample No. 7489 from Lincoln, Nebr., which was slightly bleached from weathering.

The separating of these kernels by hand in quantities sufficient for the tests involved a tremendous amount of tedious work. In separating the kernels into these three texture groups all foreign material and broken and damaged kernels were discarded. Before milling the portion representing the original sample the foreign material present was removed but not the broken and damaged kernels.

The hard red spring wheat samples, M. I. Lab. Nos. 7006 and 7276, were obtained in Oregon and No. 7066 was obtained in Minnesota. Samples Nos. 7006 and 7066 represented commercially grown wheat and No. 7276 represented the Marquis variety grown on & single experimental plot at the agricultural experiment station, Corvallis, Oreg.

The hard red winter wheat samples bear the M. I. Lab. Nos. 7005, 7154, and 7489. Sample No. 7005 was a commercially grown wheat from St. Marys, Kans. The samples numbered 7154 and 7489 were both of the Kharkof variety. The former sample was

grown at the United States Plant Introduction Station, Chico, Calif., and the latter at the agricultural experiment station, Lincoln, Nebr.

The two durum wheat samples tested bear the M. I. Lab. Nos. 7401 and 7402. These both represent true varietal wheats grown at the agricultural experiment station, St. Paul, Minn. Sample No. 7401 was of the Arnautka variety and 7402 of the Kubanka variety.

In addition to the results given in tabular form, graphs are presented for some of the more important factors discussed, that the results may be more readily compared and that the extent of the differences may be more apparent.

PHYSICAL CHARACTERISTICS OF KERNELS OF DIFFERENT TEXTURES

In Table 1 data are presented that show the test weight per bushel of the cleaned wheat in each separation before scouring, the test weight after scouring, the weight per thousand kernels, and the specific gravity.

TABLE 1.-Data pertaining to the physical characteristics of kernels of the different types of texture

TEST WEIGHT PER BUSHEL

A study of the test weights per bushel in Table 1 and in the graphs in Figure 1, shows that, of the three types of kernel textures, the mottled kernels were generally highest and the starchy kernels lowest TEST WEIGHT PER BUSHEL (BEFORE SCOURING) - POUNDS

FIG. 1.-Comparison of the test weight per bushel of the separations of dark, mottled, and starchy kernels of wheat

in test weight per bushel both before and after scouring. The differences in test weight between kernel textures were comparatively small. The kernels of dark texture averaged 62.2, the mottled 62.7, and the starchy 61.4 pounds in test weight before scouring and 62.7, 63.3, and 62 pounds, respectively, in test weight after scouring.

Although not of particular importance in connection with kernel texture, it is of interest that scouring had the effect of increasing the test weight of every one of the hard red spring and hard red winter wheat separations, whereas with the durum separations it had just the opposite effect. The reason for this reversal of effect in the case of the durum wheat separations is not known, but a similar tendency has been observed before in connection with tests on other durum samples.

WEIGHT PER 1,000 KERNELS

A considerable spread was shown in weight per 1,000 kernels. The lowest weight was 23.7 grams for the dark kernel separation of the hard red winter wheat sample No. 7005 and the highest weight was 46 grams for the dark separation of the durum sample No. 7401. Considering all the samples no consistent tendency was shown for any type of separation to weigh more than any other type. The only definite fact established by the results was that the weights of the durum separations were in every instance higher than those of the hard red spring and hard red winter wheat samples.

It might be expected that the weight per 1,000 kernels would have a consistent relation to test weight per bushel but this is not the case. For example, in the separations for the hard red winter Kharkof variety sample No. 7154 the starchy textured kernels, although lowest in test weight per bushel both before and after scouring, was highest in weight per 1,000 kernels.

SPECIFIC GRAVITY OF KERNELS

The data presented on specific gravity show a very definite relationship between that factor and kernel texture. In each sample the dark separation was highest in specific gravity and the strachy separation lowest. The mottled separations of four of the samples, however, were higher in specific gravity than were some of the dark separations from other samples.

MILLING YIELDS

In Table 2 the milling results obtained from the various types of kernel texture are given. The products resulting from the milling of these wheats were straight flour, bran, and shorts.

The results given for flour yields were in most cases highest for the dark kernels. This is particularly significant because the dark kernels were not highest in test weight per bushel. In other mill products the starchy kernels usually yielded the greatest percentage of bran and the least percentage of shorts. No consistent differences in bran or shorts yields were noticeable between the dark and mottled kernels. The durum wheat separations consistently yielded the highest percentages of flour and the hard red spring wheat samples yielded the lowest.