Dry Beans and Pulses Production, Processing, and Nutrition. Группа авторов

Dry Beans and Pulses Production, Processing, and Nutrition - Группа авторов


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to remove these heavier materials. This shaking action and the slight incline of this gravity table impart greater energy to the denser stones or mud balls. Because of the density differences, the heavier materials proceed to move up the incline and are segregated over the edge of the table.

      In the gravity separator, a large volume of dry beans is spread in a very thin layer and continuously moves over the gravity table. As this table rapidly shakes, it sorts the stones and mud balls and allows the beans to pass forward. The stones and mud balls are separated from the dry beans and are collected in a waste disposal bin. Stones and mud balls are characteristic of the geophysical structures within the bean‐growing region and may vary in size, shape, and density.

      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.

      Bingen and Siyengo (2002) reported that more sophisticated electro‐mechanical cleaning and sorting equipment has set the conditions for elevators to respond to canning and processing standards, but it has also strengthened the role for individual expertise in grading. Instead of supplanting individual judgment, the investments in more sophisticated technologies require continued reliance on human expertise (the human eye) for grading beans.

Schematic illustration of appearance of samples taken at various stages of dry bean cleaning/sorting operations.

      Source: Original images by authors.

      Dry beans are conveyed to large storage silos or steel bins for interim or long‐term storage prior to additional cleaning. The central elevating system lifts beans from the receiving pit and deposits them on conveyors in order to fill the bins. Within each bin is a device termed a “bean ladder” that will enable beans to slide in a circular path to the bottom of the bin, thus minimizing seed coat damage. It is a general practice to monitor the moisture content within the silo and use airflow from the bottom of the bin proceeding through the beans and exiting either at the top or the bottom of the bin to improve equilibration and distribution of moisture. Beans are then subjected to density separation using a gravity table. Beans are screened for size, sorted for color using an electronic eye system, and finally, stored in silos or bins prior to packaging in bags or totes, or directly shipped in bulk rail cars or trucks for delivery (Sacklin 1985; Rodiño et al. 2011).

Photo depicts dry bean receiving and storage elevator. Schematic illustration of interrelationship of factors affecting the grain and microorganism respiration in storage.

      Source: Kumar and Kalita (2017).

Schematic illustration of interaction of grain moisture, storage temperature and equilibrium relative humidity at which different organisms can grow in storage.

      Source: Bradford et al. (2018).


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