Rice processing: Pearling

Rice bran, the outer layer of the rice grain, accounts for 8–10% of the total weight of the grain; however, it contains most of the nutrients: carbohydrates (34–62%), lipids (15–20%), protein (11–15%), crude fiber (7–11%) and ash (7–10%).

Pearling is increasingly recognized by the milling and baking industry as an important stage in cereal processing because it lowers the capital investment costs, giving as well, the benefit of better-quality products.

Pearling is a process in which a grain passes through a pearling machine. Pearling is done to lower the cooking times of grains and extend the shelf life. The pearling machines used an abrasive or friction process for bran removal.

The grains pass between the rolls and the bran is gently pearled off, leaving the pretty white kernels intact. The loose bran, which is stacked to the surface of the rice after the pearling process, is removed during a polishing step.

The removed bran is collected by aspirators, whereas the polished rice is graded since it contains different-sized broken rice pieces, bran, and dust. During grading the small broken rice pieces are separated by a vibrating sieve, whereas the remaining bran and dust particles are separated by air aspiration.

Pearling is the process, prior to milling removes effectively only the bran layers from the cereal grains, allowing nutritious parts, such as the aleurone layer to remain in the intact kernels.
Rice processing: Pearling