Cereals processing technology

Cereal production methods 15
problems during slicing. Genetic variation exists in the amount of -amylase
activity both during pre-maturity and enzyme formation during post dormancy
sprouting. These two components are inherited independently giving rise to a
situation where varieties differ in their -amylase content where there is no
visible sprouting. Varieties with low -amylase activity combined with good
resistance to sprouting are favoured for breadmaking.
Grain -amylase levels reach their lowest levels during ripening, thereafter
increasing significantly. This suggests an optimum date for harvesting, but one
which is difficult to predict and achieve in practice. Nevertheless, it is good
practice to harvest crops destined for the breadmaking market early to avoid the
effects of wet weather.
Post-harvest management is an essential part in achieving high quality grain
to meet specific market requirements. Food hygiene regulations apply to stored
grain which must be protected from moulds, bacteria, rodent, bird and insect
damage, whilst pesticide residues must not exceed UK statutory levels. These
standards form the basis of recently introduced quality assurance schemes,
combining all facets of grain production from field to store and on to the mill.
Breadmaking grain harvested at moisture contents in excess of 15% must be
dried carefully at air temperatures below 60ºC to avoid denaturing the proteins,
thereby destroying the elasticity of the gluten.
For biscuit production, flour is produced from soft milling varieties with high
extensibility to ensure that the different biscuit shapes cut from the dough retain
their outline after cutting. Wheat with a protein level below 10% is preferred to
reduce gluten elasticity. The low water absorption characteristics of soft
endosperm wheat are desirable to limit the need for drying the final product to a
standard moisture content and also to reduce cracking during cooling and
subsequent packaging and storage. The -amylase content of the flour is also
less critical than it is for breadmaking.
For distilling, soft endosperm texture is required and whilst there is no protein
specification a high protein content can lead to problems with low starch and
spirit yields. Distillers often prefer to select specific soft wheat varieties that
have consistently produced high yields of spirit.
Grain quality has an extremely important influence on the suitability of a
sample of barley grain for malting. Maltsters require grain from a recognised
malting barley variety which is of uniform size with low husk and nitrogen
content with a high germination capacity. These malting characteristics can only
be accurately measured with a micro malting test which is both slow and
expensive, although the physical condition of the grain and its nitrogen content
are generally considered to be a good guide to its malting potential.
Traditionally spring varieties have commanded the highest malting
premiums, but with the increased popularity of winter compared to spring
barley in the UK, plant breeders have produced a number of good winter malting
barley varieties. All new varieties are evaluated for their malting characteristics
from micro malting tests to assess their hot water extract and are graded
accordingly. However, not all high graded varieties are approved by the Institute