Barley for Food and Health: Science, Technology, and Products

WHOLE-GRAIN PROCESSING 105
particles are subjected to shear and compression when passing between a series
of fluted (corrugated) and smooth rotating rollers followed by sieves arranged in
succession. The two steps in roller milling are the break system and the reduction
system, each of which is followed by sieving to remove the finer particles,
producing a composite flour and milling by-products. The break step splits the
kernels open, exposing the starchy endosperm while crushing the outer layers.
The reduction system consists of a series of rollers and sifters in sequence used
to reduce the particle size of the various kernel parts. These steps are repeated
until the flour quality desired is obtained. By-products are those fractions that
can yield no appreciable amount of useful flour by repeated rolling and sieving.
The two by-products are shorts and bran. Shorts represent the intermediate
by-product (defined by components) between white flour and bran and consists of
small amounts of endosperm, outer layers of the kernel, and the embryo. When
the hull is removed, as with the hulless genotype, bran is composed almost exclusively
of pericarp and testa tissue (Kent and Evers 1994; Posner and Hibbs 1997;
Owens 2001). If hulled barley is roller-milled without blocking or pearling, the
hull, being cemented to the pericarp and testa tissue, is a part of the bran.
Wheat has been researched, selected, and bred extensively for the most desirable
varieties for producing flour through roller milling. Volumes of milling
technique data are available to wheat milling companies. Such an array of information
does not readily exist for barley milling at this time. Presently there are
few or no consistent composition and quality standards available for the fractions
derived from the roller milling of barley. The terminology and composition for
barley flour and by-products have not been standardized; thus, it is reasonable
that terms and composition specifications applied to wheat milling be simply
extended to barley milling. As one would expect, barley reacts quite differently
from wheat when milled by conventional roller milling techniques to produce
flour. Barley bran is more brittle, prone to shatter in rolling, and not readily
separated from endosperm, while wheat bran is removed and separated from
endosperm tissue in large flakes. Additionally, barley flour flows less readily than
does wheat flour. The brittle characteristic of barley bran results in the production
of fine particles that increase the ash content and dark coloration of barley flour.
Nevertheless, considerable experimental barley milling has been conducted with
equipment used routinely in wheat milling, principally to investigate the feasibility
of producing barley that is acceptable for baking as well as determining the
chemical and nutritional composition of the flour and by-products (Niffenegger
1964; Pomeranz et al. 1971; Cheigh et al. 1975; Sorum 1977; McGuire 1979;
Bhatty 1987, 1992, 1993b, 1997, 1999a; Newman and Newman 1991; Wang et
al. 1993; Danielson et al. 1996; Xue et al. 1996; Klamczynski and Czuchajowska
1999; Kiryluk et al. 2000).
These early reports demonstrated the practicality of producing barley flour
using roller milling equipment and techniques designed for wheat, although many
problems were encountered. Wide ranges of flour yields and composition have
been reported along with difficulties in adequately separating the flour, shorts,
and bran factions. As a result of the early research on the roller milling of