Annatto, also known as annotta or arnotta, is a colouring matter obtained from the seeds of Bixa Orellana, Linn. (N.O. Bixaceae), a small tree growing in the East and West Indian Islands and South America. It is obtained by pulping the seeds, allowing the pulp to dry spontaneously and pressing it into cakes; or by soaking the seeds in water, allowing them to ferment, and, when the colouring matter subsides, collecting it and forming it into cakes. Two kinds are imported, the Spanish, which is made in Brazil, and flag or French annatto, made mostly in Cayenne; the former has rather a pleasant odour, while the latter is disagreeable. It occurs in the form of plastic or hard cakes, with a peculiar odour and a disagreeable saline and bitter taste. Annatto is frequently adulterated with mineral and starchy matters. It softens in water without dissolving, but is almost completely soluble in alcohol, ether, fixed oils, or alkalies, giving orange-red or dark red solutions.
Constituents.—The chief constituent of annatto is a red resinous substance named bixin (C28H34O5).
Uses.—Annatto is employed for colouring butter, milk, cheese, and various fats and oils.