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

WHOLE-GRAIN PROCESSING 97
flour through roller milling, these authors recommended conditioning moisture
levels for pearl barley and unpearled hulless grain of 13 and 14%, respectively,
followed by 48 hours of rest. Similar conclusions were arrived at by Andersson
et al. (2003) when roller-milling hulless barleys with a Bühler laboratory
mill. These authors compared no conditioning with 11.3, 14.3, 16.3, and 17.8%
moisture, followed by mixing and allowing to rest overnight. The best milling
performance was obtained with barley conditioned to 14.3% moisture. Bhatty
(1999a) roller-milled nonwaxy hulless barleys into two fractions, bran and flour,
at moisture conditioning levels ranging from 5 to 16%. He found the greatest
total yield of flour at the lowest level of moisture, but the highest levels of starch
in the flour were produced at the highest level of moisture. It is most likely that
preferred conditioning requirements for roller milling barley will depend on the
desired end product as well as the genotype and protein content of the barley.
Malting or modification of barley involves considerably greater amounts of added
moisture during steeping and germination than is required for conditioning. A
minimum of 30% and up to 50% water is added to facilitate germination in the
malting process.
Blocking and Pearling
Blocking and pearling are processes whereby the outer barley grain tissues are
gradually removed by an abrasive scouring action to produce an edible product
for food. Blocking, sometimes referred to as hulling (dehulling), is usually the
next processing step after cleaning. Blocking is designed to remove the tough,
fibrous, and largely indigestible hull that adheres strongly to the kernel. The hull
represents 10 to 13% of the dry weight of the kernel, but under some conditions,
blocking in a commercial dehulling or pearling machine may remove as much as
20% of the kernel weight. Dehulling machines are comprised of circular abrasive
stones rotating on a vertical or horizontal axis in a cylindrical chamber surrounded
by screens. The cylinder is strongly aspirated, and the degree of abrasion is
governed by the counterpressure applied at the outlet, the abrasiveness of the
stones, and the distance between the rotor and the surrounding screens (Vorwerck
1992). The pearling process that follows blocking is commonly done in three or
more stages. The latter stage or stages are sometimes referred to as polishing.
The degree of pearling, typically stated as a percentage, refers to the amount of
the kernel removed during processing. The term degree of pearling is defined
differently in different geographic regions. In the United States and Canada, for
example, 30% pearled means that 30% of the original weight is removed, leaving
70% as pearled barley. In Japan, the same product is termed 70% pearled (Yeung
and Vasanthan 2001). The material removed in the pearling process is referred
to as pearling flour, fines, orpearlings. Processing of any type will in most
cases alter the composition and ratio of nutrients in the final product(s) given the
varying concentrations of nutrients that occur in the separate tissues of the kernel.
Pearling time to achieve a specific product concentration will also vary with the
cultivar, especially between hulled and hulless cultivars and waxy and nonwaxy