Prior to the inexpensive production of gelatin and other competitive products, isinglass was used in confectionery and desserts such as fruit jelly and blancmange.
Isinglass was originally made exclusively from sturgeon, until the 1795 invention by William Murdoch of a cheap substitute using cod. This was extensively used in Britain in place of Russian isinglass. The bladders, once removed from the fish and processed, are formed into various shapes for use.
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. The finings flocculate the live yeast in the beer into a jelly-like mass, which settles to the bottom of the cask. 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.
Non-cask beers which are destined for kegs, cans or bottles are often pasteurised and filtered. 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 when it is drunk, many vegetarians consider beers (such as Guinness and almost all real ales), which are processed with these finings, to be unsuitable for vegetarian diets (although acceptable for pescetarians). A beer-fining agent that is suitable for vegetarians is Irish moss, a type of red alga also known as carrageenan. However carrageenan-based products (used in both the boiling process and post-fermentation) primarily reduce hazes caused by proteins, but isinglass is used at the end of the brewing process, after fermentation, to remove yeast. Since the two fining agents act differently (on different haze-forming particles) they are not interchangeable and some beers make use of both.