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Evaluation Process – Evaluating Flour, Dough and End Products


1. Determining Flour Quality
Flour quality means different things to different users with different end goals. Typically, some conformance to a preset standard of functionality is used to describe a flour's "quality". This standard of functionality is often based on the experience of the user in correlating a test or group of tests to his particular product. Ultimately, flour quality is defined by the flour's ability to make the desired end product to the expectations of the user on a consistent basis. Because quality flour is imperative for the production of quality baked goods, flour functionality is controlled through careful wheat selection, mill process control, and analytical testing.

Flour strength is often used to describe the quality of flour, "strength" being the flour's ability to withstand mixing, absorb water, or perform satisfactorily in an end user's baking process. It seems that there are as many ways to describe flour strength as there are baked products. In general strength relates to protein, both in the quantity available and the quality of that which is available. Protein quantity, related to the amount of total organic nitrogen, is one of the first evaluations made in determining a flour specification and – more importantly for the miller – a wheat purchase specification. But protein quantity alone is not sufficient to describe and ensure the usefulness of wheat flour. Certain other physical tests have been developed to assess a flour's usefulness related to its protein quality. These tests are often performed on flour-water doughs. Dough is defined as wheat flour moistened with water or some other liquid ingredient at a specified ratio and then blended or mixed by mechanical means. Evaluating wheat through the flour made from it begins with three basic tests: moisture, protein and ash.

2. Flour Protein
Protein is determined as nitrogen, with a factor of N × 5.7, 14% m.b. (see also chapter 2. Protein inEvaluation Process–Non Grade Factors ).

3. Flour Ash
Ash is determined on a 4 g sample in a silica dish incinerated overnight at 585 °C. After cooling, the dish and ash are weighed, the ash brushed out, the dish reweighed, and the weight of ash determined by the difference. The results are reported as a percentage. The following physical flour tests are applied beyond just moisture, protein and ash:

4. The Falling Number System
The principle of the Falling Number method is the same as that used to test wheat meal. The Falling Number method is used in the flour mill for monitoring and controlling the blending of flours and for calculation and control of malt or fungal enzyme addition. It is also used as a basic quality parameter when flour is traded. In bread, too much α-amylase activity will cause wet, sticky crumb with large voids in the loaf, and too little will cause dry, crumbled bread crumb and high loaf density.

5. Brabender Amylograph
The Amylograph performs a measurement based on the viscosity of a flour-water suspension. This test device uses a standardized heating cycle to measure the rate and extent of change in the viscosity of the suspension over time. Swelling and gelatinization of the starch thickens the suspension and thereby raises its viscosity. Enzyme activity also increases during this process. The enzymes break down the gelatinizing capability of some of the starch, which will ultimately lower the viscosity of the suspension. The increase and ultimate decrease in viscosity is measured and recorded by the Amylograph machine. This measurement can be used in much the same way as the Falling Number measurement in determining the requirement for additional enzymes to be added to the flour for optimum activity.

The new Micro ViscoAmyloGraph shown above evaluates starch or flour samples at a fraction of the standard requirements without neglecting the need for accuracy and reliability. Only 5 - 10 g of sample are needed for an evaluation. Total test time can be reduced by the elevated temperature rate increase (up to 10 °C/min). The new Micro ViscoAmyloGraph, following previous Brabender models, monitors and
records actual stock temperature. Modern correlation software allows users to compare up to 15 different curves.

6. Physical Dough Tests
Common physical (rheological) dough tests used for determining flour quality include the Mixograph, Farinograph, Alveograph and Extensograph methods. In addition to standardized tests, many millers and bakers use specific baking tests as a way of comparing the functional characteristics of different flours. A detailed background of all methods is given by Weipert. The Farinograph is generally described as a recording dough mixer. That is, it attempts to measure and report the mixing characteristics of a flour in a standard manner. Developed by Brabender around 1930, it has become the most recognized recording dough mixer in North America. Most of the flour mill laboratories in the U.S. rely on the Farinograph when evaluating wheat flour for use in breads. Fig. 17 shows representative examples of Farinograph records called Farinograms. The FarinographE is similar to the Farinograph, but the new model is a totally electronic nstrument. The previous mechanical balance system has been replaced by a sensitive, modern electronic system for torque measurement. A serial port transfers the measured data to the evaluating computer. The zero point is automatically set by the measuring system. Choosing the correct mixer sets the sensitivity range: 10, 50, or 300-gram mixer. Modern software allows the creation of master curves to be stored for quality control purposes.
Fig. 17: Representative Hard Red Winter Farinograms from the U.S. Wheat Crop Quality Book 2004
7. Baking / Product Evaluation Tests
Baking tests are also important methods of determining and ensuring quality for the commercial miller and baker. These tests often use loaf volume as the measure of flour strength. Balanced flour strength and adequate elasticity for oven expansion are critical in making quality bread products.



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