isinglass

A pure gelatin found in fish. Its particular use, for which other gelatins are not suitable, is in the clarification of fermented beverages, presumably due to its fibrous structure. The name is also applied to a form of mica, with similar appearance.

Isinglass is a substance obtained from the swimbladders of fish (especially sturgeon), used mainly for the clarification of wine and beer. Prior to inexpensive gelatin production and other competitive products, isinglass was used in confectionery and desserts such as Fruit Jelly and blancmange.

Isinglass finings are used extensively as a processing aid in the British brewing industry to accelerate the fining, or clarification, of beer. They are used particularly in the production of cask-conditioned beers, known as real ale, although there are a few cask ales available which are not fined using isinglass. Left to itself, beer will clear naturally, however the use of isinglass finings accelerates the process. Isinglass is sometimes used with an auxiliary fining, which further accelerates the process of sedimentation. The yeast in these beers tends to settle to the base of the storage tank naturally, so the sediment from these beers can often be filtered without using isinglass. However, some breweries still use isinglass finings for non-cask beers, especially when attempting to repair bad batches.

Although very little isinglass remains in the beer which is drunk, many vegetarians consider beers which are processed with these finings to be unsuitable for vegetarian diets (although it is suitable for pescetarians). The process differs, however: isinglass is added at the end of the brewing process, before bottling, whereas Irish moss is added to the hot wort while it is being boiled, and primarily reduces hazes caused by proteins.