E337

E337 is the European Union's designation for potassium sodium tartrate, also known as Rochelle salt or Seignette's salt. This crystalline solid is a double salt of tartaric acid with the chemical formula KNaC4H4O6·4H2O. It is formed by the reaction of sodium carbonate and potassium bitartrate.

Historically, potassium sodium tartrate was discovered in the mid-17th century by a French apothecary named Pierre Seignette. It found early applications as a laxative, though this use is now uncommon. A significant property of E337 is its piezoelectricity, meaning it can generate an electric charge in response to applied mechanical stress, and conversely, deform when an electric field is applied. This characteristic led to its use in early phonograph pickups and microphones.

In the food industry, E337 serves multiple functions. It is commonly used as an emulsifier, helping to blend ingredients that would not normally mix, such as oil and water. It also acts as a firming agent, contributing to the texture of certain food products. Furthermore, it functions as an acidity regulator, helping to control the pH of foods. It is found in a variety of processed foods, including cheeses, baked goods, and beverages.

Potassium sodium tartrate is generally recognized as safe (GRAS) by the U.S. Food and Drug Administration when used in accordance with good manufacturing practices. In the European Union, its use as a food additive is permitted under the E337 designation.