Kibbling and winnowing is a combined process designed to separate the shell as completely as possible from the nib. Kibble (cracking) involves lightly crushing beans which have been roasted, or partially dried, to loosen the shell. It is important at this stage to retain both nib and shell as large pieces (85-90% of particles should be over 3 mm in size) and to avoid creating fine particles the and dust.
This is best achieved by use of impact rollers, which are pairs of hexagonal rollers, rotating in the same direction, which throw the beans against metal plates. Some older machinery, which used toothed rollers to break the beans is, however, still in use
Winnowing is a separation process which depends on differences in density between the nib and the shell. Two basic fractions are