The brown rice can be obtained after cleaning, hulling, and separating, and then enter the rice mill machine for milling.The process of removing part or all of the outer skin of brown rice into white rice that meets certain requirements is called rice milling.The milling equipment used in this process is called a rice milling machine, or rice miller.Rice milling plays an important role in the entire paddy processing technology. It is the most important process in rice processing and an important link to ensure rice quality, increase rice yield, and reduce power consumption.
Purpose and Requirements of Milling Rice
The surface layer of brown rice contains a lot of crude fiber, which is difficult for the human body to digest. In addition, brown rice is not easy to absorb water and swell, which not only increases the cooking time and reduces the rice, but also has the disadvantages of dark color, poor viscosity, and bad taste. Therefore, brown rice must have its skin removed through the rice milling process.
The peeling degree of brown rice determines the accuracy of the rice. The more shell of brown rice is removed, the higher the precision of the finished rice, but the more serious the loss of nutrients. In addition to different levels of shell retention, various grades of rice also have other indicators such as impurities and shreds. In the process of brown rice whitening, under the premise of ensuring that the finished rice meets the prescribed quality standards, the rice grains should be kept intact as much as possible, and the broken rice should be reduced, rice strength and rice yield should be improved, costs should be reduced, and production safety should be ensured.
Basic Principles of Rice Milling
The skin layer of brown rice is smoother, tougher, and has a certain connection force with the endosperm. Therefore, to remove the skin layer, a certain external force is required to destroy this connection ability. Various rice milling machines that are often used at present is the mechanical force generated between the rice milling chamber components and the rice grains and the collision and friction between the rice grains and the rice grains to whiten the brown rice. According to the different properties of removing the shell, rice milling can generally be divided into three types: rubbing and whitening, milling and whitening, and mixed whitening. There are many kinds of rice mill machines currently used in our country. Commonly used are iron roller rice mills, double-roll rice mills, emery roller rice mills, air-jet rice mills, vertical emery rice mills, etc.
Evaluation of the Rice Milling Technology
The effect of rice milling process is generally evaluated from the following aspects:
① Accuracy. Rice precision is the most basic index to evaluate the efficiency of the rice milling process. Assessing the accuracy of rice should be based on the standard rice sample specified by the country.
② Crushing rate. When brown rice is whitened, its volume and weight will be reduced due to the shedding of the cortex and embryo. The percentage of reduction in the crushing rate. Since most of the crushing is the skin layer, the crushing rate is also called the chaff removal rate. The higher the precision of the rice grains, the greater the crushing rate, and the general weight reduction is about 5%~12%.
③ Brown rice out white rice rate. The brown rice out white rice rate refers to the percentage of the amount of white rice that comes out of the machine to the amount of paddy that enters the machine. This is an important criterion for evaluating the effect of rice milling technology. The higher the processing precision, the greater the crushing rate, and the lower the white rice yield.
④ Broken Rice Rate and Increase Rate.
The broken rice rate refers to the percentage of broken rice in white rice.
It is the main indicator for evaluating whether the finished rice meets the quality requirements.
The increase rate refers to the increase of the broken rice rate in white rice compared to the broken rice in brown rice.
⑤Roughness Uneven Rate. This is a reflection of the inconsistent precision of white rice.