Cereals processing technology

5.7.1 Frozen rice
Frozen cooked rice is convenient to use since it requires less time to prepare than
raw rice. The rice may be frozen plain or in combination with other foods. Rice
is an integral part of frozen dinners. A commonly used method for preparing
frozen cooked rice is as follows:
• Soak long-grain rice (Indica type) in an abundance of water at 54–60ºC,
which contains enough citric acid to reach a pH of 4.0–5.5. Sufficient water
should be used to cover the rice after soaking for 2 h.
• Drain off the excess soaking water, and rinse with more of the same pH water
to remove fines.
• Drain thoroughly, tapping the screen to shake loose the adhering water. The
soaked, drained rice is placed in layers 5 cm deep or less over a screen
supported above the water in the pressure cooker. Place a small volume of
water at the bottom of the pressure cooker. Close the vessel, and heat with the
vent open until steam is emitted to expel air in the retort. Close the vent, raise
the steam pressure to 2.09 kg/sq cm, and hold for 12–15 min. Then blow off
steam gradually to prevent violent boiling and flashing.
• Place the hot steamed rice in a large amount of water at 93–99ºC without
stirring. The rice will imbibe water until the grains are large, tender, and quite
free. Stirring will cause the rice to become sticky. The rice should be held in a
perforated vessel so that water may circulate freely through it.
• Cook by boiling the rice for 10–15 min. Drain off the hot water, and rinse
twice with cold water that has the pH adjustment described above.
• Tap and shake to remove the free water, or suck off the free water over a
vacuum filter.
• Convey the cooked rice on a stainless steel mesh belt through an airblast
cooler to reduce it to room temperature, and then package in cartons or plastic
pouches. Freeze the rice in air-blast freezers. The rice can also be frozen as
individually quick-frozen (IQF) products prior to packaging in a fluidizedbed
freezer.
Frozen storage at 18.8ºC for up to one year has no deleterious effects on quality.
Prechilling the cooked rice results in removing most of the surface moisture
and at the same time permits quick-freezing. Before freezing takes place, the
individual grains are separated and kept out of contact with one another during
the freezing process. The product is then frozen solid. Excellent results have
been obtained by subjecting the rice to a moving air-blast at 34ºC. After the
grains are solidly frozen, they can be packed in any desirable manner.
5.8 Extruded rice
Rice production 101
Rice breakfast cereals may be divided into two classes: those requiring cooking
before serving and those ready to eat directly from the package. Here, we will
concentrate on the processing of ready-to-eat breakfast rice cereals.