isinglass

Isinglass is a form of collagen obtained from the dried swim bladders of certain fish, most commonly sturgeon. The bladders are cleaned, salted, dried, and processed to yield gelatin that dissolves in water and forms gels when cooled. Isinglass has long been used as a fining agent to clarify liquids such as wine, beer, cider, and fruit juices. When added as a solution, it binds with suspended haze-forming compounds (proteins, phenolics, and tannins) and settles to the bottom, allowing the clarified liquid to be racked away.

Beyond beverage clarification, isinglass has a history as a fish-based adhesive, known as isinglass glue, used in bookbinding, woodworking, and artwork restoration. In the food industry, it is one of several animal-derived gelatins used as a gelling or thickening agent in desserts and confections, although modern substitutes such as plant-based gels are increasingly common.

Isinglass is not suitable for vegetarians or most vegans because of its fish origin, and it may pose risks for individuals with fish allergies. In contemporary winemaking, many producers replace isinglass with alternatives like bentonite or PVPP, though it remains used in some traditional methods and regions. Historically, its versatility extended from clarifying beverages to providing adhesive transparency in various crafts.