Milling Quality of Wheat
Important properties are :
1.Purity of the wheat, i.e.
dockage or Besatz and other impurities
The lesser the admixture, the higher the value of the wheat.
Mechanically operated apparatuses (e.g. Granotest) have been developed in
recent years to ascertain the percentage of impurities. The evaluation is done
by a standard method.
2.Test weight (bushel or
hectoliter weight)
The viewpoints differ greatly as to the significance of these factors
to milling. It is in any case an accepted fact that these factors are not
always indicitive as to the milling quality of wheat.
The hectoliter weight of a first class wheat can e.g. decrease from
81.5 kg to 72.5 k, merely through contamination on with small quantities of
powder (sand, dust). The milling quality is not necessarily reduced in this
case. Vice versa variations in the test weight due to oily substance are also
noticeable. It is generally known that hectorliter weight (HL) is also
influenced by moisture content, decreasing by 0.4 kg every percent of water.
The HL-weight increases again during drying, but will not attain the original
value again, due to permanent deformation of the kernels.
Test were made by Bruckner for the purpose of substituting the
unreliable test weight by other better systems, but these were not generally
acceptable. That is the reason why the test weight system is still used today
as a basis for evaluation. A high test weight is always a certain
recommendation for the corresponding wheat. A correlation to the milling value
can exist within one and the same type of wheat measured under standardized
conditions.
Note :
1 U.S. Bushel of an average weight of 60 lbs = 27.215 kg
1 quarter = 290.8 Liter
The average specific weights of the various parts of a wheat kernel are:
3. Vitreous Kernels
Wheats with a vitreous or glassy cross-section are generally
preferable. Vitreousness indicates a compact kernel composition, a higher
protein and a good semolina structure. Especially important in Durum wheat.
Vitreousness can decrease under the influence of moisture and heat, even in the
field. The % vitreous kernels is an important factor determining the quality of
Durum wheat. Kernels can be partly vitreous and partly mealy.
4. Moisture Content of Wheat
Moisture content has a marked influence on flour yield, apart from its
importance in the storage of wheat. Of course the higher the moisture content
of wheat, the lower the amount of dry matter in the kernel. Flour can only be
produced from the latter. Furthermore, if distributed too evenly in the whole
kernel, moisture will cause trouble in the separation of the endosperm from the
bran.
Another point is the control of the most favorable moisture content
immediately before milling. No dry matter is lost in this case and this
conditioning simplifies milling a great deal.
5. Flour Content of Wheat
The potential flour content of wheat can be determined fairly exactly
by test milling in the BUHLER Automatic Laboratory Mill MLU-202, combined with
an analytical test of the flour and the offals. This will be found to vary
between 77 and 84% (on a dry matter basis = d.m.) according to kernel
development. Lower results are of course obtained with abnormal kernels.
Baking Quality of Wheat
This method of evaluation can as a rule be performed with the flour
obtained by test milling on the above mentioned Laboratory Mill. Wheat grains
and flour, or doughs are subjected to chemical and physical analysis. The
results can additionally be confirmed by a baking test if carried out by a
competent baker.
A difference is made between rapid methods (e.g. Sendimentation test
of Zeleny, gluten washing with the determination of the swelling figure, etc.)
and more elaborate methods. It is obvious that the rapid tests can only give an
approximate picture of the whole quality complex. This can be valuable in
commercial practice though, if carried out exactly as prescribed.
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