1NDUSTRIAL A N D ENGl NEERING CHEMIisTRY
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SYMPOSIUM O N BREAD Papers presented before the Joint Session of the Division of Industrial and Engineering Chemistry and the Division of Agricultural and Food Chemistry a t the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 t o 14,1923.
Variations in Wheat Types
Triticum
. satiuum, L a m .
I{
,polonicum, Linn.,
dicoccum Schr emmer, spelta, ~ z ; l n $elt . tenax
o u l h ? . Vill., common wheat compacturn, Host., club wheat turgidurn, Linn., poulard wheat durum, Desf., durum wheat
Polish wheat
material, and test weight. Some attention is given to kernel characters, but comparatively little to the physiological characters of milling and baking quality, except as these may inadvertently be involved in the subclass and in the numerical grade assigned on account of quality, condition, mixture, or foreign material, and test weight. We are interested primarily in the milling and baking or the bread-making values of these wheats. The ultimate relative market value of these wheats depends upon the estimation of milling and baking value after making certain physical and chemical tests. There are a large number of varieties included under each class of wheat, Some of these varieties are well known throughout the whole section producing wheat of this class; other varieties are known only locally. HARDREDSPRING WmAT-Of the hard red spring varieties, Fife and Bluestem have been perhaps best known and most widely distributed, but are now being rapidly displaced by Marquis. The Fife wheat of this country dates back to 1842, when David Fife, of Otonabee, Ont., received from a friend in Glasgow, Scotland, a small package from a shipload arriving from Danzig, Germany, but supposedly of Russian origin. Later investigation indicated that the wheat originally came from Galicia. There have been many synonyms, such as Red Fife, Scotch Fife, Canadian Fife, Powers Fife, Wellman’s Fife, etc. It is a hard red spring wheat with a short kernel having a wide, deep crease. A number of different varieties of wheat have borne the name Bluestem, but the particular one referred to in the Dakotas and Minnesota is a hard red spring wheat with glumes pubescent and kernels narrower and longer than Fife. It shows excellent milling and baking qualities. Marquis is of hybrid origin, a cross between Hard Red Calcutta and Red Fife, made by William Saunders. It is a high yielding, early maturing variety of the Fife type, and one of our best varieties when judged from the milling and baking standpoint. HARD REDWINTERWHEAT-In the hard red winter wheat class, the varieties Turkey, Kharkov, and Kanred are best known and most widely distributed. Turkey was brought into south-centrctl Kansas in the early seventies by the Russian Mennonite settlers. The plant is very winterhardy and drought-resistant, giving good yields. The kernels are long, hard, dark red with tight crease. This variety is especially prized for its high milling and baking value. The Kharkov variety was probably originally identical with the Turkey, although it comes from the province or government of Kharkov, about two hundred miles further north than Crimea, the original home of the Turkey. Kanred is quite simiIar to Turkey, but somewhat more winter-hardy and rust-resistant. It is the product of a single head selection from the Crimean variety, made in 1906 by H. F. Roberts, of the Kansas Agricultural Experiment Station. Samples of Kanred and Turkey grown under the same conditions have been subjected to milling and baking tests, with practically identical average results. It may be interesting to note here that John H. Parker, of the Kansas Agricultural Experiment Station, has made some
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
crosses between Kanred and Marquis which are very promising. If he has succeeded in combining the good qualities of both varieties so as to secure an early, rust-resistant, highyielding wheat with the best of milling and baking qualities, such result will be a real and worth-while achievement. SOFTRED ’C~INTER WHEATS-The soft red winter wheats have been most widely known through such varieties as Fultz, Fulcaster, Mediterranean, and later varieties such as Jones’ Winter Fife, Mealy, and Harvest Queen. These varieties, like those of the hard wheats, represent both bearded and beardless types. The chief difference between the hard and soft wheats is the difference in texture of kernel. The endosperm of typical kernels of soft wheat is entirely soft and mealy or starchy, while that of typical kernels of hard wheat is hard and horny or vitreous throughout. However, each class produces wheats which approach the other class until there is an overlapping in kernels that are semihard. WHITE J F 7 ~ ~ ~ ~ s - Twhite h e wheats are quite widely distributed throughout the United States, and are represented by a large number of varieties, some of the most important being White Australian (also known as Pacific Bluestem), Dawson’s Golden Chaff, Gold Coin, Defiance, Rig Club, and Little Club. A large number of the wheats of the Pacific coast and the intermountain area belong to the white wheat class. These white kerneled varieties are easily distinguished from the red wheats by their appearance, and also, as a rule, possess lower milling and baking qualities. DURUMWHEATS-The durum varieties belong to a class distinctly different from the common bread wheats. The plants all have the spring habit of growth, the leaves have larger, broader blades, and the spikes are compact and very heavily bearded or awned. When true to type the kernels are very hard and horny. I n all but a few red varieties the typical kernels are clear or translucent and generally referred to as amber colored. The durum wheats have been widely grown in the United States only during the last twenty years, and on account of their drought-resistant qualities are particularly adapted to the arid portions of the western spring wheat States. The two best known and most widely distributed varieties are Arnautka and Kubanka.
VARIATIOKS IN WHEAT From the wheats belonging to the five great classes, the miller selects and blends until the mixture going to his rolls will produce a type of flour that will satisfy his customers, and his big problem is, once he has his product established, to maintain a uniform quality from day to day and week to week throughout the year. This is no easy task because of both physical and chemical variations in his raw product. He has to contend with varietal differences within a given area and, what is usually more important, he must deal with differences w i t h a given variety due to climatic and soil conditions. In some States, such as Ohio or Pennsylvania, the variations in climatic conditions will not be great, and the varietal differences will be more manifest. I n States like Xorth Dakota or Kansas, where the rainfall may vary from over 30 inches in the eastern to less than 19 inches in the western part and the altitude also increases as the rainfall decreases, the variations in composition due to climatic difference far exceed those due to variety. VARIATION I N PROTEIN CONTENT-The amount Of protein in relation to carbohydrates is the factor showing greatest variation and, as this corresponds very closely to the amount of gluten, it is a most important factor. The soft
red winter wheats and the white wheats, each considered as a class, average considerably lower in protein than the hard red wheats or the durum wheats, the usual range being from about 7 to 11 per cent in the soft wheats, while the hard wheats may contain anywhere from 8.5 to over 23 per cent. A limited amount of rainfall with some hot winds during the latter part of the fruiting period results in failing to store sufficient carbohydrate material to produce a plump kernel; hence the resulting kernel is shriveled, of low test weight and low flour yield, but high in gluten content. Usually this gluten is of good quality, Ptrong yet elastic, but sometimes it is tough and inelastic, or a t other times it is sticky or runny. Usually the quantity of wheat having good quality of gluten is rather limited and the miller must resort to blending wheats with glutens of opposite qualities in an effort to produce a blend that will have gluten satisfactory in quality and quantity. YELLOw-BERRY-Whi1e different lots of hard winter wheat consisting wholly of hard and vitreous or flinty kernels may show considerable difference in protein content, a more marked difference is usually shown by the soft, mealy, or partially soft kernels known as “yellow-berry” hard wheat. It is also true that such wheat is lacking more in quality than in quantity of gluten. Hackel, in describing the yellowberry conditions, says: If the albuminoids so fill up the intervals between the starch grains that the latter seem to be imbedded in cement, the albumin appears translucent and the fruit is called corneous; but if the union is less intimate, there remain numerous small air cavities and the albumin is opaque and the fruit is mealy. Both conditions may occur in the same variety of wheat.
The yellow-berry, then, appears to be a distinctly physiological growth product due to certain conditions thus far not clearly analyzed nor satisfactorily explained. Authorities, after many years’ investigation into the causes of yellow-berry and means of prevention, do not agree. It seems quite probable that there are many contributing factors causing yellow-berry and that under certain conditions a single factor may be the controlling one, while under different conditions the effect) of this particular factor is not recognizable. Le Clerc and Yoder2 in their triangular experiments demonstrated that climate has a much greater influence than soil upon the percentage of yellow-berry and upon the chemical composition. Headden3 states that his experiments did not substantiate the claim sometimes made that climatic conditions favorably influence the development of or cause yellow-berry. On the other hand, he states that yellow-berry can he very much lessened or entirely prevented by the application of a sufficient quantity of available nitrogen; that yellowberry can be greatly intensified or increased by the application of available potassium; that yellow-berry is not indicative of an exhausted soil; that the presence of yellowberry indicates that potassium is present in excess of what is necessary to form a ratio to the available nitrogen present, advantageous to the formation of a hard, flinty kernel; furthermore, that yellow-berry is under the control of the grower, If there should be sufficient difference in the price of grain produced, he could control it with a margin of profit. These conclusions were drawn from a comparatively limited number of experiments carried on in the State of Colorado. Whether or not these principles can be applied throughout the country seems somewhat doubtful. Experiments carried on at the Kansas Agricultural EXperiment Station show that the per cent of yellow-berry 2
J. A g u . Research, 1, 275 (1914).
8
Colo. Agr. Expt Sta
, Bull.
205.
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December, 1923
1NDUSTRlAL A N D ENGINEERING CHEMISTRY
and composition of the seed wheat have no effect upon the per cent of yellow-berry or the protein content of the resulting crop; furthermore, that proper crop rotation and proper seed-bed preparation have a beneficial effect upon milling and baking value of the wheat; and that apparently some varieties are more resistant t o the common factors which usually result in increased percentage of yellow-berry. It is probably not necessary to state that crop rotation and proper seed-bed preparation bring sufficient yield increase to pay several times the additional cost of production, even though an improvement in milling and baking quality were not secured.
Flour Manufacture By C. H. Bailey UNIVERSITY OF MINNESOTA, ST. PAUL,MINN
HE success of the roller milling process is dependent upon the fact that substantial differences exist in the physical properties of the several wheat kernel structures. Thus, the branny covering of the berry is distinguished by its tough, fibrous character. The germ, or embryo, is rich in fats and oils, and hence tends to flake when crushed between rollers. The endosperm, or floury portion, on the other hand, is friable and tends to fracture when struck. It is impossible, however, to effect a quantitative separation of the various kernel structures in roller milling. Small quantities of the fibrous bran and the oily germ find their way into the flour, and particularly into the low or clear grades. A substantial proportion of endosperm or floury material is likewise to be found in the by-products, bran and middlings. Commercial bran not infrequently contains 15 to 20 per cent of flour, while commercial standard middlings are often found to contain 30 per cent or more of flour. It accordingly follows that, of the 82 to 85 per cent of endosperm (potentially flour) to be found in the average plump wheat kernel, not to exceed 7 2 to 75 per cent of the kerntsl is separated in the form of straight grade flour. I n the modern roller mill the first important process is cleaning and conditioning the grain. Commercial wheat frequently contains a considerable quantity of foreign matter, including weed seeds, sticks, stones, fragments of straw, etc. An effort is made to separate these from the wheat as completely as possible before the latter is ground. Northwestern grown hard spring wheat contains more of this foreign matter or dockage than does any other class of American wheat, and a variety of cleaning appliances are necessary to the separation of the foreign matter in this wheat. Certain of the weed seeds, which are most difficult of separation, are of interest to the chemist because of constituents which they contain. Thus the seed of the corn cockle, Agrostemma githago, contains a saponin which is reported to be somewhat toxic. The seed of the wild vetch, Vicia angustifolia, is very yellow, owing to the carotinoid pigments which it contains, and a cyanogenetic glucoside found in this seed yields hydrocyanic acid and benzaldehyde when treated with warm water. If wild vetch seed is present in wheat in excess of 1 per cent a t the time of milling, the characteristic odor of benzaldehyde will be observed in the dough when the flour is mixed with water. Seeds of the giant ragweed, commonly known as “king heads” in the grain trade, if present in wheat a t the time it is ground, result in flour of less desirable properties. It is accordingly necessary that such seeds be separated before attempting to grind the wheat.
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The spores of bunt or stinking smut are frequently found in commercial grain, particularly from western areas, and relatively small amounts of this material will darken t h e flour appreciably. Several special treatments are resorted to in order to remove these smut spores, including scouring with bolted air-slacked lime, and washing with liberal quantities of water. I n the latter event special machinery must be available for “whizzing” the wheat in a centrifugal drier to remove the excess of water. It is a common practice to add appreciable quantities of water to dry wheat before grinding, in an effort to enhance the toughness of the branny covering. This water may be added in the wet washing process or may be sprayed upon the grain in what is commonly known as the tempering process. Frequently, cold wheat is warmed slightly before the tempering water is added. The moistened grain is held for a few hours in order that the bran may absorb the added water, but the period is so adjusted that no substantial penetration of the water into the endosperm results. The cleaned and tempered wheat is then crushed by passing it between corrugated steel rollers. The individual rollers of the pair revolve a t different rates of speed, the differential being commonly about 2.5 to 1. After the first breaking or crushing of the wheat, the resulting chop is bolted and the coarse material reground between another pair of corrugated break rolls. Five or six breaks are ordinarily provided in hard wheat mills, and after the last break the coarse material is known as bran. In addition to the coarse fractions scalped from the break roll chop, two other classes of materials are separated on bolting this chop. The fine portion which will pass through a bolting silk is known as break flour, and is sprouted directly to the flour bins. Fragments intermediate in size between the coarse fraction and the flour are known as “middlings.” These are further classified by passing them over a sieve in a machine known as a purifier, which effects a separation on the basis of size of particles. In addition, a fan a t the top of the purifier box draws an air current through the sieves, which lifts out light, fibrous particles. The purified middlings are then ground between smooth steel rollers and the ground material is bolted to remove the fine particles of flour, Coarse fractions which failed to pass through the flour sieves are reground twice or three times. The flour produced by each regrinding of this material contains increasing proportions of fiber, ash, and soluble proteins, and becomes progressively darker in color. From this description of the process it is evident that a considerable number of flour streams will be found in a flour mill, one such stream resulting from each break and each middlings reduction. Not uncommonly twenty t o twenty-five or more flour streams are thus available to the miller, and he may combine any or all of them to suit the demands of the trade, While the individual flour streams may be bleached, the more common process when bleaching is resorted to is to treat the finished products with bleaching agents. The most common bleaching agents used in American inills are: (1) Nitrogen peroxide, ordinarily generated in the mill by means of a flaming electric arc. ( 2 ) Chlorine, which is usually purchased in a liquid form in steel drums, often mixed with small percentages of nitrosyl chloride. Chlorine is generated by the electrolytic process in a few mills. Occasionally, a double treatment with chlorine and anhydrous ammonia is resorted to. (3) Nitrogen trichloride produced commercially by passing gaseous chlorine through a solution of ammonium sulfate. (4) Benzoyl peroxide, added in mixture with acid calcium phosphate below the second break roll.
Numerous criteria of flour grades have been proposed by cereal chemists during the past half-century. Among
