The Milling of Flour

The following discussion of the milling process is quoted from Pyler (3). A full description of wheat types, wheat class differentiation, wheat grades, and the structure of the wheat kernel, is beyond the scope of this presentation.  The following information is presented as background to the topic of the classification of flours in the US and Europe. The botanical species under discussion is Triticum aestivum (T. vulgare), or common wheat:

"The wheats selected for milling must be adapted to the requirements of their intended end uses. Thus, bread flours are milled from hard wheats, cake and pastry flours from soft wheats, and pasta flours from durum wheats. Moreover, given the variations in character among varieties within the major wheat classes, another vital operation of the miller is to blend wheats of different varieties and from different sources to yield flours of the desired protein content and uniform baking performance…

The series of individual break and reduction operations in the milling process gives rise to as many as 150 different product streams in a modern flour mill…

Depending on which flour streams are combined to yield the final product,  [Artisan Note:the separation of the grades of wheat is accomplished by a sifting process] different commercial flour grades are obtained. When all the streams are combined, the result is a so-called "straight" flour. Frequently, the more refined streams are kept separate and sold at a premium as patent flours, while the remaining lesser streams yield so-called "clear" flours. The most common types of commercial flours include "fancy patent," which contains 40 to 60% of the total flour yield; "short patent," which comprises [the next 20%] or the 60 to 80% [percentile] of the straight flour; "medium patent," with [the next 10%]  80 to 90% [percentile] of the straight flour; and "long patent" with [the next 5%] 90 to 95%  [percentile] of the total flour. The clear flours that remain after each separation of the patent flours are designated as "fancy clear," "first clear," and "second clear," respectively, the degree of refinement decreasing in that order. The lower grade clear flours are too dark in color and too poor in baking quality to make satisfactory bread flours. Some of the better grades are used for admixture with rye flour, while the lower grades find uses outside the baking industry. The various grades of flour differ in their chemical and physical characteristics and require different treatment in the bakery…

The relationship and the percentages of the various flour grades obtained from wheat can be seen in Chart 1 by clicking on the "Extraction Rate Sample Window".  [NOTE: To print the contents of the window, right click your mouse, then click "Save image as..". Once saved the image can be printed as usual.]  Of interest is the fact that 100 lb. of cleaned wheat yields 72 lb. of flour and 28 lb. of feed material.  Wheat, on an average, contains about 85% of endosperm. It is evident, therefore, that an extraction rate of 72% falls short of the potential yield.  This failure to extract all of the endosperm as flour, even with advanced milling methods, is caused by the fact that the peripheral zones of the endosperm adhere so firmly to the aleurone and bran layers that complete separation is not practical under commercial milling conditions…"

The following information relative to the ranges to be expected in various batches of wheat flour  was obtained from Quaglia, in the Manuale del Panificazione (3), and is summarized in Table I.  It summarized   by Professor Quaglia as follows:

"The chemical composition of the flour depends upon the characteristics of the wheat and the extraction rate; in general the variations can range in the following manner:

Table I

Starch 64 - 71%
Insoluble Proteins (Gluten) 9 - 14%
Soluble Proteins 2 - 4%
Sugars 1 - 2%
Fat 1 - 2%
Mineral Substances 0.3 - 0.7%
Water 1 - 15%

Manuale de Panificazione (1) and Professor Quaglia's  book  Scienza e Technologia Panificazione (4) are  gold mines of information about bread making and flour.  Neither has yet been translated into English.

The information presented in Table II was excerpted from a text by  Capello (5) and displays these variations according to specific rates of extractions:

Table II

Component 50% Extraction 72% Extraction 80% Extraction 85% Extraction Whole Wheat Extraction
           
Water 14.5 14.5 14 14 14
Proteins 6 - 7.5 8 - 11 8 - 13 9 - 14 10 - 15
Starch 72 - 74 65 - 70 64 - 69 64 - 68 60 - 65
Sugars 1 - 2 1 - 2 1 - 2 2 .0- 2.5 1.6 - 2.0
Lipids 0.4 - 0.6 0.8 - 1.0 1.0 - 1.5 1.2 - 2.0 2.0 - 3.0
Cellulose 0.1 0.15 - 0.20 0.2 - 0.4 0.6 - 1.0 2.0 - 5.0
Minerals 0.2 - 0.5 0.3 - 0.6 0.6 - 0.8 0.7-  0.9 1.5 - 2.5

The variations above, while seemingly small are not insignificant and are responsible for some notable differences   found in flour quality.