TECHNOLOGY OF CEREALS (pericarp) and possibly the embryo. greater severity, or retreatment of already abraded tocks, removes part of the endosperm also Grains are brought into contact with an abra ive surface, which may be of natural stone carborundum, sculptured or perforated metal, or other material. Where perforated screens are used, these behave as sieves also selec. tively permitting passage of particles. In the present context abrasion is used to include the similar process of attrition. There is a nice Diagonal rolls distinction between the two terms, depending on the roughness of the surfaces involved but it is insufficient to warrant separate considera- tion. When used specifically to remove the outer tissues of caryopses either process may OOO be described as decortication 2. Severe abrasion includes heavy or protracted grinding between surfaces such as those of a pestle and mortar and of grinding stones; it Horizontal rolls features therefore in many of the simple FIG 6. 1 Disposition of rolls in roller mill stands. The fast and historical methods used for preparing roll of each pair is indicated by the broader arrow ground meals. Such grinding may reduce grains to a range of particle sizes including Break rolls that of four Ro∥ er milling Whole grains or partially milled stocks are Roll fluting assed between rotating rollers for several reasons including 1. Grinding -a process in which grains are British reduced to smaller particle siz stages are performed within rollermills, each of which is equipped with a pair of rolls Rollstands usually consist of two mills back- to-back, within the same housing but operat ing independently and on different feedstocks The rollers may be disposed diagonally, verti- FIG 6 of break rolls. In the enlarged view of the ally or horizontally. They are aligned in nip' olls are disposed in the dull-to-dull configura parallel and rotate in opposite directions. One tion. Details of typical British and U.S. roll flutings of the rolls rotates faster than the other so that a speed differential exists(see Fig. 6.1) The rollers may be smooth surfaced resembles an italic v, with one side shorter futed, but when used in a grinding mode they than the other (fig 6.2) rotate at different speeds As the flutes are asymmetric the rolls On fluted rolls the profile of each flute be run with either the steep(sharp)sive surface, which may be of natural stone, carborundum, sculptured or perforated metal, or other material. Where perforated screens are used, these behave as sieves also, selec￾tively permitting passage of particles. In the \A/ be described as decortication. 2. Severe abrasion includes heavy or protracted