Organic matter enters the Bayer process during the formation of alumina from bauxite ore via dissolution in concentrated sodium hydroxide at high temperatures. This organic matter interferes with the crystallisation process in a number of ways. The nature of this organic matter is reviewed on the basis of molecular weight. While its function is not fully established, and the prevention of its role has yet to be achieved, much is known about its interaction. Two principle new discoveries have been made, namely 1) a host guest structure to the organic matter, and 2) that a variety of structures exist at different molecular weights. Rather than molecular weight fractions being simple polymers or alike macromolecules, they vary considerably in chemical structure from char to benzoic in nature. This means that organic matter exhibits an array of interactions modes during the crystallization of alumina.