Cereals processing technology

84 Cereals processing technology
chalk as genetic and environmental conditions allow. Kernels inherently free of
chalkiness are one of the first quality characteristics breeders select for in new
US varieties. Chalkiness in rice is often referred to as ‘white belly,’ or
‘immature,’ depending on its location on or within the endosperm. Close visual
examination is used most for determining type and amount of chalkiness.
Translucency instruments offer promise as objective measures of transparency,
including chalkiness, in rice.
Milling quality and yield
No rice variety can be commercially successful unless it possesses high wholekernel
(head) and total milled rice yield. Whole-kernel (head) yield is the
quantity of intact whole kernels (including broken kernels three-quarters or more
in length) of well-milled rice obtainable from given quantities of rough (paddy)
rice. Total milled rice yield includes whole kernel (head) and all other sizes of
broken kernels obtainable from specified amounts of rough rice. The objective
of rice milling is removal of hulls, bran, and germ, with minimum breakage of
endosperms. Milling quality in rice is based on yield of whole-kernel (head) rice
because it is the milled product of greatest economic value. Yield of total milled
rice is important, and is influenced by proportion of hulls and amounts of fine
endosperm particles.
Several laboratory instruments are available for determining milling yield in
rice. Two commonly used methods are: (a) the official grading method for
determining milling quality of rough rice by United States Standards for Rice
(USDA 1982 with changes 1982–1990), 30 which requires 1000-g rough rice
(McGill #3 Mill), and (b) a modification of the official method requiring only
125-g rough rice for analysis. The modified method is used in rice-breeding
programs, rice mills, and processing plants.
Milling quality is usually reported as a percentage of whole-kernel (head) rice
and total milled rice obtained from a unit of rough rice. Average milling yields
of whole kernel rice was 55–63% from long-grain rice, and 57–66% from
medium- and short-grain types.
Cooking and processing quality indexes
Cooking and processing quality, with milling quality, are fundamental
components of quality that determine and establish economic values of rice.
Conventional cooking and processing US rice
Average values for some comparative chemical and physical (quality)
characteristics of typical cooking and processing long-, medium-, and shortgrain
US rice types are given in Table 5.2. The values shown are representative
of each grain type although environmental factors influence these characteristics
to some extent. 32,33
Chemical and physical characteristics associated with traditional cooking and
processing of southern US long-grain types are: an intermediate to relatively
high amylose content, a slight to moderate reaction of whole-kernel milled rice