 "Whole offerings" were quite rare in early times, but as the ritual became more fixed and statutory, and the concentration of sacrifice into a single sanctuary (particularly after Josiah's reform) made sacrifices quite distinct from simply killing animals for food, "whole offerings" gradually rose to great prominence.The burnt offering is believed to have evolved as an extreme form of the "slaughter offering", whereby the portion allocated to the deity increased to all of it.In "slaughter offerings", the portion allocated to the deity was mainly the fat, the part which can most easily be burnt (fat is quite combustible); scholars believe it was felt that the deity, being aethereal, would appreciate aethereal food more than solid food—the burning of the fatty parts of animals being to produce smoke as a "sweet savour" for the deity.