Isinglass

Lore & Background

Isinglass has been produced from the swim bladders of fish, originally exclusively from sturgeon—particularly beluga. The English word derives from the obsolete Dutch huizenblaas, where huizen refers to a kind of sturgeon and blaas means bladder, or from the German Hausenblase with the same meaning. In 1795, an invention by William Murdoch facilitated a cheap substitute using cod, which was extensively used in Britain in place of Russian isinglass; in the United States, hake was important. In modern British brewing, all commercial isinglass products are blends of material from a limited range of tropical fish.

Before the inexpensive production of gelatin and other competing products, isinglass was used in confectionery and desserts such as fruit jelly and blancmange. It is also used as an adhesive to repair parchment, stucco, and damage to paintings on canvas. Pieces of the best Russian isinglass are soaked overnight to soften and swell, then cooked slowly in a double boiler at 45 °C with stirring; a small amount of gum tragacanth dissolved in water is added as an emulsifier. When repairing flaking paint on parchment, isinglass can be applied directly to an area soaked with a small amount of ethanol, guided under a binocular microscope. It can also be used to coat tissue or goldbeater's skin as a temporary backing. As a dried film, the adhesive can be reactivated with moisture, and for this use it is cooked with a few drops of glycerin or honey. It has greater adhesive strength than many other adhesives used for parchment repair.

Reader's Guide

Isinglass finings are widely used as a processing aid in the British brewing industry to accelerate the clarification of beer, particularly in cask-conditioned beers. The finings flocculate live yeast into a jelly-like mass that settles to the bottom of the cask, speeding a process that would otherwise occur naturally. Some cask ales are available that are not fined using isinglass. Non-cask beers destined for kegs, cans, or bottles are often pasteurised and filtered, and the yeast in these beers tends to settle naturally, so sediment can often be filtered without isinglass; however, some breweries still use it, especially when attempting to repair bad batches.

Many vegetarians consider beers processed with isinglass finings unsuitable for vegetarian diets, though acceptable for pescetarians. A beer-fining agent suitable for vegetarians is Irish moss (a red algae containing carrageenan), but carrageenan-based products primarily reduce hazes caused by proteins, while isinglass removes yeast after fermentation; they are not interchangeable, and some beers use both.

Isinglass finings are also used in the production of kosher wines, though for reasons of kashrut they are not derived from beluga sturgeon because this fish is not kosher. Whether the use of nonkosher isinglass renders a beverage nonkosher is a matter of debate in Jewish law; Rabbi Yehezkel Landau, in Noda B'Yehuda, first edition, Yore Deah 26, permits such beverages, a position followed by many kashrut-observant Jews today.

The similar-sounding names have caused confusion between isinglass and waterglass (sodium silicate), especially as both have been used to preserve eggs: a solution of isinglass was applied to eggs and allowed to dry, sealing their pores, while eggs were submerged in solutions of waterglass, forming a gel of silicic acid that also sealed the pores.

Did You Know?

• In 1795, William Murdoch invented a cheap substitute for isinglass using cod.
• Isinglass can be reactivated with moisture when used as an adhesive for parchment repair.