Relatively high wheat prices, variation in wheat quality arriving in the mill from different parts of the world, larger capacity milling units and diversification of customer demands are just some of the variables that require careful analysis and fine tuning in wheat buying and processing.
To be more specific, usually the value of a wheat types or a mix of wheat types to be processed in a mill is of great concern and a challenge to the wheat buyer and miller. The first issue is wheat cost, which accounts for about 75% of the turnover in the mill. The other issue relates to how the wheat will perform on the mill.
The long sought-after approach among wheat buyers and millers is the quantification of the two parameters to allow evaluation and an estimate of the economic as well as the technical values of wheat. Different methods and models were suggested in the past, all of great value in the evaluation and management of flour milling operations.
This article describes a new simplified approach that combines the evaluation of wheat based on its technical performance as well as its relative economic value estimation.
The suggested method is based on the parameters of wheat ash, flour ash and flour extraction. Ash is the remaining mineral residue following a complete incineration of the organic material from a sample described in Approved Method 08-01 (AACC International 2000). It is expressed as a percentage of the original sample and corrected to a moisture basis. The ash in the whole kernel varies significantly based on variables that relate to variety, type of soil, and climatic conditions.
The wheat arriving at the mill, unless identity preserved (IP), is usually a homogeneous blend of different varieties and with an average level of ash. Most of the kernel ash is concentrated in the areas adjacent to the bran and in the bran itself. High ash content accumulated in the wheat kernel during growing is found also in the endosperm, and is inherently bound to give higher ash or mineral content in the produced flour. Variables such as flow sheet design and mill adjustment can control the level of outer wheat kernel layers that contain more minerals or ash in the flour.
In the past, flour ash was a value that characterized flour type and quality. The content of ash or mineral in the flour indicated the degree of separation between wheat kernel parts varying in their ash content. Currently, flour quality is determined more objectively in the mill laboratory and processing plant based on generated data with sophisticated rheological, spectroscopic equipment and analytical methods. I and others have stated in the past that ash or the mineral content of flour is not an objective characteristic to determine the quality of flour. It is suggested here that ash, or the mineral content of wheat kernels, intermediate and final materials from the milling process, is one of the main tools the professional miller should be using for mill adjustment and flow sheet optimization.
There is a high correlation between ash content of wheat and the resulting flour. Technical performance of a wheat lot on a particular milling unit with a certain flow sheet can be determined by the ash content of the total extracted flour. In general, the miller adjusts the system to maximize flour extraction while minimizing the ash content or bran particles in the flour.
When comparing two or more kinds of wheat on a milling unit, the flour ash content at the maximal extraction is divided by the whole wheat kernel ash.
Previously, I used the ratio of flour ash to wheat ash (FA/WA) to show the difference in technical milling performance of two wheat types using the same flow sheet. When using the FA/WA ratio, values are expressed more objectively as a measure of wheat performance on a given milling system independent from the whole-wheat ash. Values of FA/WA are drawn against the flour extraction (see Figure 1, page 54).
Milling units differ in their flow sheets, adjustment and final results. Even if flow sheets and equipment of adjacent milling units are similar, produced flours from the same wheat are never the same. Differences in performance and flour qualities exist even if the same conditioned wheat is used on both units. Accordingly, in plants where several operating milling units exist, performance of each should be evaluated separately.
Beside all other numerous parameters that affect the processing of wheat, the flour extraction and its relation to the ratio of FA/WA is the most important link between technological and economical performance of the processing unit. The evaluation method suggested in this article is based on numerous observations and data evaluation in various commercial mills.
An Excel spreadsheet is used for the data mathematics, algorithms and graph drawing (see Table 1, top left). The ratio FA/WA were values corrected to the same moisture bases and drawn (vertical axis) against the straight grade flour yield (horizontal axis). The angle for each of the wheat types is determined using the trigonometric tangent by dividing the FA/ WA value by the flour extraction value as shown on the graphs.
The lower a1 = 18.6 for wheat No. 1, even with the higher whole wheat and flour ash, indicates a better technically performing wheat or wheat mix on the particular milling unit than wheat No. 2 with a2=21.500.
The angle a can be reduced by improved wheat evaluation and selection, and improved conditioning. The milling unit performance can be improved by making necessary changes in the mill flow sheet to accommodate wheat characteristics (hard or soft), control capacity, grinding roll adjustment, purifiers’ adjustment, and various other technical changes in the operating milling unit. All above are technical adjustments that the professional miller can implement to increase technical performance with a certain type of wheat, namely to decrease the a value.
The economic performance difference expressed as the "cost ratio" is the value of each of the wheat types milled on the unit compared to the best performing wheat. The relative cost comparison could be evaluated based on distance between the lines of the least performing wheat (largest a) to the best performing wheat line (smallest a). The cost of the best performing wheat on the mill is the basis for determining the base value of other types of wheat to be milled.
Based on the performance ratio, the maximum acceptable wheat price can be determined. In figure 1 (page 54) assuming flour extraction rates of 78% and 76% for wheat No. 1 and No. 2, respectively, the vertical line from the total flour extraction point of the least performing wheat to the horizontal flour extraction coordinate creates the "cost ratio line." The ratio of the distance between the lines from the lower extraction point of wheat No. 2 to the line of wheat No. 1 and dividing by the distance to the horizontal shows the relative higher value of wheat No. 1.
In the example shown, the value of wheat No. 2 should be about 17.23% cheaper than wheat No. 1 for the particular milling unit. The difference in cost ratios of the wheat types and performance on the particular milling unit is not related to the currency in which it is bought.
Figure 2 (page 54) shows an actual situation in a particular commercial mill where three wheat types were milled on the same unit separately. For the particular mill, the economic value of wheat No. 2 is 4.77% lower than wheat No. 1. For the same mill, the economic value of wheat No. 3 is 6.33% lower than wheat No. 1. Not aware of the analysis, a higher price was actually paid for the lower performing wheat type.
The same rationale can also be used when evaluating a certain wheat blend performance on a milling unit. In the case of wheat blends, the cumulative a is calculated. Based on the example in Figure 2, if the percentages for wheat No. 1, No. 2, and No. 3 in the blend were 50%, 35%, and 15%, respectively, the cumulative a will be: 29.8(0.50) + 30.9(0.35) + 31.3(0.15) = 14.9+ 10.82+ 4.69= 30.37.
Initially, to reduce the a value of the blend, each wheat type should be milled separately on the mill to see its performance relative to the other types. Another method is experimentally milling each kind of wheat on a batch-type system that is highly correlated to commercial milling. Flow sheets are available for the batch type experimental milling to produce 74% to 82% flour extractions.
A complete mill analysis should be performed on a commercial milling unit and different methods should be used to identify the key stages where changes should be considered. Only with such means is it possible to reduce the a value and improve the mill performance. Here is where the "art of milling" is still the leading concept, not as a means of producing artistic results, but in the absolute dedication of the miller to performing mill analysis and adjustment to achieve the best results from a lot of wheat.
Dr. Elieser Posner is an international consultant with more than 50 years of activity in operation, research and teaching of wheat milling. He can be reached at