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
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.
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| 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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