does not materially affect the color and, on account of its high gluten content, it enhances the bread-making quality.

It seems unnecessary to take space here for more than a brief outline of the roller process, especially since detailed and illustrated descriptions are so readily obtainable from some of the large millers.

Wheat which has been screened and cleaned is first passed between a pair of corrugated rollers, known as the " first break,” where the kernel is flattened and somewhat crushed and a small amount of flour known as the "break" or "first break " flour is separated by means of sieves while the main portion is conveyed to the "second break" where the kernels are more completely flattened and granular flour particles are partially separated from the bran. The material passes over several pairs of rollers or breaks, each succeeding pair being set a little nearer together. This is called the "gradual reduction process,' and effects a more complete separation of the flour and bran than was possible in the older processes in which the wheat was ground fine in one operation. The effect of passing through these rollers is to pulverize the inner floury part of the wheat grain, to flatten the bran (and germ), and to break up the intermediate portion into what is called "middlings." The flour is obtained by sifting, the bran and dust are separated from the middlings by means of coarser sieves, aspirators, and other devices, and the purified middlings are then passed between smooth rolls, where they are reduced to the desired degree of fineness, or, as it is sometimes expressed, where the granulation is completed.

The best grades of patent flour are not made entirely smooth and homogeneous, but are rather made to have a characteristic feel, which is due to the granulated middlings which these flours contain. A flour which has no granular feeling is not usually considered of the highest grade, but is generally rated as a soft wheat flour of poorer gluten. On the other hand, the flour

should not be too coarsely granulated, and the miller in order to obtain the desired product must be careful in blending the powdered flour obtained from earlier breaks with the granular flour obtained from the middlings.

The flour from the middlings finally passes through silk bolting cloths of 100 mesh or finer, the dust and particles of débris having been removed at various points in the milling process.

In some large mills in order to secure a better granulation and more complete removal of the offals the grain passes through so many rollers and sieves that 40 or more different streams of flour are obtained from the same lot of wheat. Many of these streams are then usually brought together to produce the finished flour of the ordinary commercial grades. The break flours are those obtained from the earlier crushings of the wheat and consist mainly of the innermost powdery portion of the grain, while the patent flours contain more of the harder portion known as the middlings, but no absolute definition of the term "patent flour" can be given because of differences in usage in different parts of the country. Generally the first and second patent flours are spoken of as "high grade," which term may also include what is called "standard patent flour " or " straight grade flour"; or the "straight grade" may be divided between the high grade and low grade classes. To the low grade flour belong what are called the "second clear" and the "red dog." About 72 per cent of the clean wheat is recovered in the higher grades of flour and about 2 or 3 per cent as merchantable white flour of lower grade. The higher grades are characterized by a lighter color, more elastic gluten, better granulation, and a smaller number of débris particles. The low grade flours contain a somewhat higher percentage of protein but are not as valuable for bread-making purposes because the gluten is less elastic.

Technical terms of the flour trade are sometimes confusing. Thus " 95 per cent patent" means that 95 per cent of the total

flour (not of total grain) is included in the patent, while an "85 per cent patent" is a higher grade of flour which constitutes only 85 per cent of the total flour obtained in the given process.

The composition of the mill products of wheat may vary both with the wheat and with the details of the process. The following analyses (Table 36) are for products all milled by the modern roller process from the same lot of Minnesota hard spring wheat and are therefore strictly comparable with each other. The differences of composition are therefore properly attributable to the separations effected by the milling process alone.

TABLE 36. ANALYSES OF WHEAT AND THE Products of RolLER MILLING (United States Department of Agriculture)

These analyses show a gradual increase in the protein content 1 from first patent to "red dog" flour, but the "red dog" flour, while containing the most protein, is the poorest grade of flour

Note that in the above table the percentage of protein is that of nitrogen multiplied by 5.7 for the reason explained above (page 299). Increasing the protein figures in the above table by one tenth gives essentially the results which would be obtained by the use of the more common factor 6.25.

from the standpoint of the baker, and in the milling of wheat it often is allowed to remain with offals and sold for cattle food. It will also be seen that the percentage of ash is lowest in those flours which are commercially rated as of highest grade and increases as we go down the list to the lower commercial grades of flour. Patent flour rarely contains more than 0.55 per cent ash and usually contains less than 0.5 per cent.

Snyder points out, however, that noticeable variations occur in the amount of mineral matter or ash in different wheats. It may also be pointed out that the ash constituents of wheat are many of them of distinct nutritive value, so that it is only from a commercial and not from a nutritive standpoint that we would classify a flour as low grade because it has a relatively high ash content.

Another study of the mill products of wheat made by Teller at the Arkansas Experiment Station, 1894 to 1898,1 included a milling experiment in which the principal products of a long process (7 break) roller mill were analyzed with the following results:

13.75 13.90 13.22 12.25 12.85

13.90 6.80 0.33 0.47 0.90 3.12 5.80 2.15 4.65 0.17 0.26 0.74 3.55 6.14 2.17 1.60 1.05 1.25 1.70 4.80 5.20 2.15 14.38 9.69 10.37 12.88 16.36 15.56 12.31 36.00 75.01 73.75 70.56 54.45 63.32

59.02

1.70 1.82 2.26 2.87 2.73 2.16

1 Bulletins 42 and 53, Arkansas Experiment Station (Fayetteville, Ark.).

36.55

6.34

* For explanation of this factor for estimating protein from nitrogen see page 298.

In this investigation Teller also determined the amount of each of four different forms of nitrogen compounds in each of the main mill products, with the results shown in Table 38.

It will be seen that the higher commercial grades of flour, that is, those most prized for bread-making, show the largest proportion of gliadin whether this be reckoned in percentage of the gluten or of the total proteins present. The quality of making an elastic dough capable of large expansion in the breadmaking process depends upon both the amount and the nature of the gluten. In order to make a large light loaf of bread, the flour should have a fairly high gluten content, and its gluten should contain a high proportion of gliadin.

TABLE 38. DISTRIBUTION OF NITROGEN IN MILL PRODUCTS (TELLER)

Analyses of flours with reference to their bread-making value often include determination of total nitrogen and of the "gliadin number" which shows what percentage of the total protein is in the form of gliadin.

Absorption, expansion, and baking tests may also be required in an examination of flour as to its bread-making qualities. Directions for making such tests may be found in Leach's Food Inspection and Analysis.