isinglass, a particularly pure protein obtained from the bladders of sturgeon and other freshwater fish that has been used for fining wine for centuries. As early as 1660, King Charles II of England regulated the use of isinglass by merchant vintners.
Like gelatin, isinglass reacts with the excess tannins in harsh young red wines. Although expensive, and difficult to prepare, isinglass is also occasionally used in the clarification of white wines to be bottled without a final polish filtration, as it has about the same clarifying property. However, there is a noticeable trend away from the use of animal-derived products for fining, mainly in the interests of vegetarians and vegans.
