Читать книгу Dry Beans and Pulses Production, Processing, and Nutrition онлайн

200 страница из 239

Bean size separation is achieved by screening over a series of sieves. This screening provides increased uniformity of size and shape within a specified lot of beans and separates materials, which are both larger and smaller than the desired bean. Thus, beans are collected as either “overs” or “throughs” with respect to the individual sieve size. The overs are materials that do not pass through the screen and the throughs are materials that do pass directly through the sieve. With the proper size configuration of a series of screens, the vast majority of both oversized and undersized material will be readily eliminated. Large seeds, small seeds, splits, stones, and additional mud balls can be removed through various screening operations (Uebersax and Siddiq 2012).

A final cleaning stage incorporates color sorting by equipment that possesses a series of photoelectric cells commonly referred to as electric eyes. Each individual bean is viewed for appearance. Each bean is channelled past a photoelectric cell positioned within subdivided individual lanes; discolored beans are rejected by a blast of air. This highly sophisticated cleaning system will result in improved uniformity of beans possessing “good” color with limited damage (Uebersax and Siddiq 2012). It is noted that beans of contrasting classes and other grains are removed based on color differences.