There are two ways to mill rice: chemical and mechanical. The chemical method also includes solvent extraction and rice milling and enzymatic rice milling. Solvent extraction and rice milling, first soften the brown rice cortex with rice bran oil, and then lightly whiten. In the process of grinding, spray with rice bran oil and n-hexane mixture continuously to form “fine rain” moisturizing, and finally obtain non-destructive low-temperature white rice. , by-product rice bran oil and edible defatted rice bran. Enzymatic hydrolysis of rice is the use of fiber enzymes as a “cutter” to cut the cortical fibers into short and loose shelves. The brown rice cortex can be peeled off without milling, and the task of rice production is completed. However, the chemical investment is large, the cost is high, and the economic benefit is poor. It has not been promoted and applied.
In China, the mechanical method has been widely used to produce rice. It uses the mechanical force generated by special equipment (rice mill machine) to peel and whiten brown rice. If the force mainly pressures, the form of peeling is regarded as rubbing; if peeling is achieved at high speed, the form of peeling is converted into grinding. In general, the two characteristics co-exist in the device, but it seems to be weak in different models.
The effect of rubbing comes from the relative movement between the walls and between the grains. When the binding force between the cortex and the endosperm is less than the frictional force, the cortex will be pulled off and erased, and the appearance of the brown rice will be white. However, when the friction is not greater than the structural strength of the endosperm, the grain is intact. In order to achieve the best of both worlds, it is suitable for the processing of brown rice with high strength and soft skin. For brown rice with weak strength, it is easy to cause broken rice. The force of milling mainly comes from the high-speed rotation between the inner roller and the outer cylinder and the sand blade of the surface diamond grains. The brown rice is continuously crushed as a sandwich in the chaotic travel, causing the cortex to rupture and fall off, and the brown rice is whitened. The characteristics of this whitening are low pressure, high linear velocity; large centrifugal acceleration, which is suitable for the processing of brown rice with weak strength and hard surface. Although the broken rice is small, the beige color is dark, the light is not smooth, and the accuracy is not easy. Evenly. The two kinds of whitening have their own advantages. In practice, most of them are used in two kinds of whitening, and they are used to avoid shortness to achieve better results.
The main working part of the rice mill machine is a whitening chamber formed by a rotating roller and a steel plate punched with a sieve. Due to the push of the pusher and the blocking action of the outlet pressure gate, a large pressure is generated between the rice grain and the coarse rice roll, between the rice grain and the rice sieve, and between the rice grains in the whitening chamber, and the surface of the brown rice is formed. Milling, wiping off, removing rice skin. The milled rice husk is discharged from the sieve hole of the rice sieve to become rice bran. Rice bran is usually sent to the by-product processing process by pneumatic conveying.
Adjusting the feed flow rate or adjusting the outlet pressure door can change the pressure inside the whitening chamber. The greater the pressure, the more severe the grain is milled. The higher the removal rate of rice, the higher the accuracy of white rice, and the higher the amount of broken rice.
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