The next time you are about to throw out all your old sturgeon bladders, resist the temptation. Instead, peel the outer skin from each bladder and wash what is left in cold water. Next, remove the bladder’s inner skin and squish it with a bowling ball until it becomes a nearly-clear ribbon. You can then use this substance—called isinglass—to thicken jellies or soups, which is what people have done with isinglass for centuries. Although the substance is semi-transparent, isinglass does not really get its name from its resemblance to either ice or glass. Instead, the word isinglass derives from huysenblas, a Middle Dutch compound formed from huysen, meaning sturgeon, and Has, meaning bladder. When the word huysenblas was introduced to English in the mid sixteenth century, however, the spelling was changed to isinglass, partly because the see-through nature of the gelatin reminded people of glass.
A gelatine derived from the swim bladder of specific fish, typically available in the shape of thin, nearly see-through sheets. Nowadays, it has been largely replaced by commercial gelatins.
Isinglass is a type of pure gelatin that is practically flavorless. It is produced from the air bladders of various fish, with sturgeon being a common source. This substance finds extensive commercial use in the clarification of beer and wine. Additionally, isinglass is employed in the preservation of eggs.