Process for par-boiling rice

Details Process for par-boiling rice Process for par-boiling rice

1990-05-07

1992-07-14

Yeung, George

Food or edible material: processes, compositions, and products

Direct application of electrical or wave energy to food...

Heating by electromagnetic wave

99330, 99516, 426461, 426462, 426511, A23L 100, A23B 900

Patent

active

051301539

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for par-boiling rice and in particular, but not exclusively, to such a process using microwaves to heat the rice.
The process of par-boiling rice has been known for at least a hundred years and was originally carried out in order to facilitate the removal of the husk from paddy rice. (Paddy rice, or rough rice, is the term used in the art to describe rice as it is harvested which has only been treated coarsely to separate the majority of non-rice contaminants from the rice. Paddy rice comprises the rice kernel, its surrounding bran layer and an outer husk). It was found that this process also resulted in the dehusked rice becoming less attractive to rodent pests, more nutritious and less sticky after cooking.
It has since become common practice in rice growing areas to par-boil rice on an industrial scale to improve the properties of the rice. Generally speaking the par-boiling processes are carried out on paddy rice. In fact, as far as the Applicants are aware, all commercial par-boiling processes use paddy rice. However, some publications show small scale laboratory tests using very special, complicated and expensive methods to par-boil cargo rice (cargo rice is paddy rice from which the husk has been removed). Such methods have not been used commercially.
A typical industrial par-boiling process involves steeping the pad rice in water at about 70.degree. C. for about 2.5 hours to raise the water content of the rice from 12% to about 35%. As long as the water temperature is kept below the gelatinisation temperature of the starch in the rice (about 70.degree. C.) the rice will eventually reach an equilibrium value for its water content of about 35%, the time taken to reach this value being dependent on the water temperature. If the water content is raised above this figure it is likely that the rice will split open due to the effects of the absorption of the water. However, if the water content after steeping is significantly lower than this, the final product of the process will contain a large number of "white bellies" (which are grains in which the starch is not fully gelatinised).
In order to facilitate the steeping step, some industrial processes apply a vacuum to the rice after the addition of the water to remove air from the rice and then apply pressure, generally of about 2 bar, to the water to increase the rate of water penetration into the kernel.
Once the water content of the paddy rice has been raised to the desired level, the starch in the rice kernel is gelatinised, generally by steaming the steeped paddy rice at 100 to 120.degree. C. A typical steaming step is carried out at 110.degree. C. for 2 to 15 minutes. The product of the steaming step is paddy rice having a high water content and having the starch in its kernel gelatinised.
It is therefore necessary to dry the steamed rice. This needs to be done very carefully in order to avoid breaking the rice kernels. Originally it was carried out very slowly by leaving the rice out in the sun at ambient temperature for a few days. However, as this involves a long time delay, industrial processes generally use a drying schedule as follows. The steamed paddy rice is dried by use of hot air to a water content of about 22%. In this stage most of the water is removed from the outside of the grain and very little from the inside. This stage takes about 35 minutes.
The partially dried rice is then tempered by leaving it at ambient temperature for about four hours. During this time water equilibrates throughout the grain. Thereafter the tempered paddy rice is dried to a moisture content of 16 to 18% by use of hot air. This takes about half an hour. The rice is then finally dried by blowing air at room temperature over it for up to six hours to bring its water content to about 14%.
After the rice has been fully dried, it is dehusked in conventional manner to produce par-boiled brown or cargo rice (which comprises the rice kernel and the surrounding bran layer). Thereafter, the rice may be polished to remove the

REFERENCES:
patent: 2498573 (1950-02-01), Ozai-Durrani
patent: 2515409 (1950-07-01), Jones et al.
patent: 2546456 (1951-03-01), Landon et al.
patent: 4361593 (1982-11-01), Brooks et al.
patent: 4810511 (1989-03-01), Velupillai et al.

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