Cereals processing technology

14 Cereals processing technology
80 kg hl for plump, well filled grain. Breadmaking samples are normally over
76 kg hl. Seasonal variation in specific weights of individual varieties is quite
marked, largely on account of differences in radiation and rainfall during the
grain filling period. However, management practices are also important in
ensuring that the plant remains free of pests and disease and is supplied with
adequate nutrients and water.
Hard wheat is required for inclusion in breadmaking and a soft texture is
required for biscuit making. When hard wheat is milled the endosperm cells
separate along the cell wall margins into easily sifted particles, and the bran is
easily separated from the endosperm to give a high extraction of white flour,
capable of high water adsorption during dough production. Soft wheat has a
much lower extraction rate and the flour consists of a mass of fine cell debris
with poor flow characteristics and a lower water adsorption capacity. Endosperm
texture is under genetic control with varieties either classed as hard or soft. This
character is simply inherited and easily managed within breeding programmes,
whilst agronomic practices have no influence on this quality component.
Wheat flour is used for breadmaking as a result of the viscoelastic properties
of the dough when water is added. The dough may be classed as either strong or
weak, depending on the quantity and quality of the grain proteins, which in turn
influences gluten strength. For breadmaking, gluten must be strong enough to
retain the carbon dioxide generated during fermentation, allowing the bread to
rise. The protein content of wheat grain varies widely, but for breadmaking a
value of at least 11% is required. In practice high grain protein levels are
achieved through the application of nitrogen fertiliser above the optimum for
yield. This is especially beneficial when applied late in the season. Foliar
applications of urea applied during the milk development stage have been found
to be particularly beneficial. Recent work has also demonstrated the importance
of supplying the crop with an adequate supply of sulphur at a time when
atmospheric depositions have declined significantly as a result of reduced
pollution. Applications of around 20 kg S ha in spring have been shown to
improve the breadmaking characteristics of wheat grown in sulphur-deficient
areas of the UK.
Protein quality is strongly influenced by genotype, although husbandry and
environmental factors can also play an important role. Low grain sulphur will
result in low concentrations of the sulphur-containing amino acids, cystine and
methionine, and may result in poor loaf volume. Protein quality has also been
shown to fall as a result of late fungicide sprays that prolong the grain filling
period.
During seed germination endosperm starch is converted into soluble glucose
and maltose to support the developing embryo. This is brought about by
enzymatic activity, especially the enzyme -amylase, present within the grain
and activated during the germination process. Some -amylase activity is
needed to release sugars and aid fermentation during the breadmaking process.
Excessive -amylase levels result in the formation of a darkened loaf crust as a
result of sugar caramelization and a sticky crumb structure which can cause