Carrageenan is obtained by extraction with water or alkaline water of certain species of the class Rhodophyceae (red seaweed). It is a hydrocolloid consisting mainly of the potassium, sodium, magnesium, and calcium sulfate esters of galactose and 3.6-anhydro-galactose copolymers. The relative proportion of cations existing in carrageenan may be changed during processing to the extent that one may become predominant.

Carrageenan is recovered by alcohol precipitation, by drum drying, or by freezing. The alcohols used during recovery and purification are restricted to methanol, ethanol, and isopropanol.

The commercial products classified as carrageenan are frequently diluted with sugars for standardization purposes and mixed with food grade salts required for obtaining gelling or thickening characteristics.