Rice is harvested in the Mid-South
at moisture contents (MCs) typically
ranging from 13% to 22% (wet basis).
Because these MCs are greater than
those safe for long-term storage, rice
is dried within a fairly short period
after harvest to 12% to 13% MC
before being placed in storage. Once
dried, “processing” of rough rice into
milled rice takes place throughout
the year and consists of several
operations.
After cleaning to remove foreign
material, rough rice is hulled to
produce brown rice. The hull represents
approximately 20% of the mass
of a rough rice kernel. Brown rice is
usually milled immediately after
hulling, removing the bran layers and
germ by frictional and/or abrasive
action. The bran represents approximately
10% of the original rough
rice mass.
The remaining milled or “white”
rice comprises head rice, defined as
those kernels retaining three-fourths
or more of their original length, and
broken kernels (brokens). The milled
rice yield (MRY) represents the mass
of milled rice expressed as a percentage
of the original dried rough rice
mass. Typical MRYs range from 68%
to 72%. Upon removal of brokens, only
head rice remains. The mass of head
rice, expressed as a percentage of the
original rough rice mass, is defined as
the head rice yield (HRY). Head rice
yields can vary from 0 (all kernels are
broken) to a theoretical maximum of
approximately 70% (no kernels are
broken). Milling quality is often
expressed as a ratio of the HRY to
the MRY, e.g., a 58/70 value would
indicate an HRY of 58%, MRY of