Carrageenans are a family of linear sulphated polysaccharides that are extracted from red seaweeds. They are widely used in the food industry, for their gelling, thickening and stabilizing properties. Their main application is in dairy and meat products, due to their strong interactions with protein. There are three main varieties of carrageenan, which differ in their degree of sulphation. Kappa-carrageenan has one sulphate per disaccharide. Iota-carrageenan has two sulphates per disaccharide. Lambda carrageenan has three sulphates per disaccharide. Gelatinous extracts of the Chondrus crispus (Irish Moss) seaweed have been used as food additives for hundreds of years. Carrageenan is a vegetarian and vegan alternative to gelatine in some applications, although it cannot replace gelatine in confectionery like jelly babies.

There are three main commercial classes of carrageenan:

Kappa forms strong, rigid gels in the presence of potassium ions; it reacts with dairy proteins. It is sourced mainly from Kappaphycus alvarezii.

Iota forms soft gels in the presence of calcium ions. It is produced mainly from Eucheuma denticulatum.

Lambda does not gel, and is used to thicken dairy products. The most common source is Gigartina from South America.

In the production of carrageenans, only methanol and ethanol can be used to facilitate the refining process and no other organic precipitant should be used.