One of the important steps in the making of leather is the process known as bating or puering. This operation consists in treating the limed, unhaired skins with materials containing a proteolytic enzyme absorbed on an inert material, plus a deliming salt such as ammonium sulfate. The object of the process is to reduce some of the alkalinity of the skin and remove, from the grain surface particularly, any substance which would interfere with subsequent tanning operations.