Cereals processing technology

Rice production 83
Table 5.1 Range of average grain size and shape measurements among conventional
US long-, medium-, and short-grain rice a
Grain Grain Length Width Length/ Thickness Grain weight
type form (mm) (mm) width (mm) (mg)
ratio
Long 6.5–7.5 1.9–2.2 3.0:1–3.7:1 1.5–1.8 15–21
Medium Milled b 5.4–6.0 2.3–2.7 2.1:1–2.6:1 1.7–1.9 17–21
Short 5.0–5.2 2.5–2.9 0.7:1–2.0:1 1.8–2.0 18–22
Long 6.8–8.0 2.0–2.3 3.0:1–3.8:1 1.6–1.9 16–20
Medium Brown c 5.8–6.3 2.4–2.8 2.2:1–2.7:1 1.8–2.1 18–22
Short 5.2–5.4 2.6–3.0 1.8:1–2.0:1 1.9–2.1 20–23
Long 8.7–9.9 2.3–2.5 3.4:1–4.0:1 1.8–2.0 21–24
Medium Rough d 7.8–8.4 2.9–3.2 2.5:1–2.8:1 1.9–2.2 23–25
Short (Paddy) 7.2–7.3 2.9–3.4 2.1:1–2.4:1 2.0–2.3 24–29
a
Based on measurements of clean, mature grains of conventional varieties from Uniform
Performance Trials, TX, LA, AR, and MS.
b
Whole milled kernels with hull, bran, and germ removed.
c
Grain with hull removed.
d 31
Unhulled grain.
but it varies with factors such as pubescence, amount of dockage, unfilled and
immature kernels, and grain type.
General appearance
Many factors constitute general appearance in rice. Some, including grain size,
shape, and uniformity, vitreousness, translucency, chalkiness, color, and
damaged and imperfect kernels, are equally important contributors to general
appearance.
Translucency
Translucent kernels are demanded by practically all segments of the rice
industry. Typical nonwaxy US varieties are required to possess these traits to a
high degree. Consequently, rice breeders practice intensive genetic selection for
bright, clear, translucent kernels in new varieties at all stages of varietal
development.
Chalkiness
Chalkiness detracts from general appearance and usually results in lower milling
yields since chalky kernels tend to break more during milling. Excessive
chalkiness is undesirable for many processed products because of nonuniformity
produced by overprocessing chalky kernels under usual processing conditions.
Chalkiness occurs when rice is harvested at too high a moisture level or in
varieties of nonuniform maturity in which excessive numbers of immature
kernels exist. Both type and amount of chalk are, in many instances, highly
heritable, and intensive selection is carried out to develop varieties as free of