No-washing rice processing and technology
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The production of rice-free rice involves a meticulous and advanced processing method that goes beyond traditional rice milling techniques. The core requirement is the use of high-quality rice, followed by a series of enhanced steps including cleaning, shelling, separation, whitening, deep grinding, polishing, grading, and sealed packaging. This process can be summarized as: initial cleaning → shelling → coarse separation → brown rice selection → whitening and grinding → deep milling → white rice polishing → final grading → sealed packaging. Compared to conventional methods, the key differences lie in the brown rice selection, deep milling, and white rice polishing stages.
Studies have shown that relying solely on basic cleaning is not enough to remove all impurities. During the milling process, new contaminants such as husks, ash, and other foreign particles are introduced. To address this, an additional step of selecting and removing unpolished grains is incorporated. This ensures that only pure brown rice enters the milling machine, which is crucial for maintaining the quality of the final product. In addition to removing impurities, this stage also helps classify brown rice by size, improving grain uniformity and enhancing the overall quality of the end product.
During the brown rice selection phase, a planar rotary sieve is used to eliminate fine dust, lumps, ash, and most of the defective grains. Using holes of 20 mm x 20 mm or Φ3.2 mm, the removal rate of fine and coarse grains can reach 100%, while imperfect particles are removed at an 80% rate. Large grain brown rice extraction exceeds 55%. Additionally, stones and light impurities are removed using a density separator and winnowing. In Chinese rice mills, these impurities—such as leftover husks and stalks—are often concentrated during coarse grain separation and then further processed through supplementary winnowing and density sorting, significantly contributing to the quality of unwashed rice.
Traditional whitening technology often uses one or two machines, which can lead to excessive peeling, affecting the surface finish and hardness of the rice, and increasing the breakage rate. To avoid this, the process is divided into three stages of whitening, known as "three whites." The first grind removes about 4.5–5% of the brown rice weight, the second removes another 4.5%, and the combined total of the first two grinds accounts for around 9%, equivalent to the entire outer layer of the grain. The third grind removes 2–3%, mainly from the sub-aleurone layer, which is rich in protein, fat, and B vitamins, making it highly nutritious and fully edible.
Multi-machine whitening requires careful adjustment of roller speeds and the ratio between sand rollers and iron rollers. For example, sand roller machines typically operate at 1,400–14,050 rpm, while iron roller machines run at 900–950 rpm. In China’s existing mills, adding a third blower machine to the original two can enhance efficiency, allowing some second-stage rice to be reprocessed for high-quality no-scoop rice production.
Polishing white rice is a critical step in producing rice-free rice. A water-based polishing agent is sprayed onto the rice grains, forming a thin gel film that gives the rice a pearl-like luster and a clear, jade-like appearance. Some polishing devices use two chambers with iron and non-toxic nylon rollers. As the rice enters the chamber, heat from the solution and the polishing roller causes the surface to gelatinize, creating a shiny, polished look. Italian manufacturers may even spray Vaseline oil to achieve a similar effect.
Another technique reported in Japan involves treating polished rice with warm water (55–60°C) for 10–15 minutes to dissolve surface dirt or grease. Temperature and time must be strictly controlled—too low or too short, and the effect is minimal; too high or too long, and ethanol could penetrate the grain, posing safety risks. After treatment, the rice is dried quickly to remove any residual ethanol. Drying methods include hot air, cold air, natural drying, or vacuum drying. For example, 80°C hot air for 5 minutes followed by 20°C cold air for 10 minutes achieves the desired result effectively.