Cereals processing technology

82 Cereals processing technology
Recently, long-grain rices with superior processibility, referred to as
‘Newrex/Rexmont’-type quality, were developed for a drier and fluffier table
rice with improved processibility for manufacturing into canned soups, quickcooking,
and frozen rice products. Newrex/Rexmont-type quality represents the
first major improvement in US long-grain quality and is the forerunner in
superior processibility.
5.2.2 Components of rice quality
Hull and bran (pericarp) color
Rice produced in the United States is classed as either light (straw)- or dark
(gold)-hulled. Although hull color is not a major concern in producing regular
white milled rice, it is important in processing parboiled rice. Varieties with
light-colored hulls are preferred by parboilers than dark-hulled varieties
parboiled under similar conditions. Genetic selection for light-hulled varieties
is an important consideration in developing new varieties suitable for parboiling.
Selection for hull and bran color is accomplished by close examination or by
colorimetric methods.
Grain size, weight and uniformity
Rice is marketed according to three grain size and shape classes (long, medium
and short). Kernel dimensions are primary quality factors in most phases of
processing, drying, handling equipment, breeding and grading. Grain size and
shape are among the first quality characteristics considered in developing new
varieties. Intensive genetic selection is practiced to eliminate heritable
abnormalities such as: deep creases, which tend to leave bran streaks on
milling; irregularly shaped kernels; sharp-pointed extremities, which break
easily in milling; and oversized germs, which detract from milling quality and
grain appearance.
The various grain types are classified according to length, width, thickness
and grain weight (Table 5.1). Methods for measuring rice grains include use of
photographic enlargers to magnify kernels or simply measuring with a ruler the
length, width, and thickness of several grains placed in adjacent positions for
particular measurements. 31 Uniformity of grain size, shape and weight is
determined by calculating the coefficient of variation for measurement on
randomly selected grains of representative samples. Grain weight (size) is
expressed in g/1000 grains or mg/grain.
Test weight
Test weight is a comparative indicator of total milled rice yield. It also
provides relative measures of dockage and/or foreign material present and of
proportions of unfilled, shriveled, and immature kernels. Test weight of rice is
the weight of a known volume. Test weight is expressed in pounds per
Winchester bushel. To convert to kilograms per hectoliter, multiply by a
factor of 1.287. Average test weight of US rough rice is 58 kg/hl (45 lb/bu),