Proteins

Protein based compounds are the most diverse and commonly used class of fining agents in winemaking. The general action of protein fining agents is binding with wine tannins, and many of these agents are used to soften the flavor of overly tannic red wines. Many of these agents will also help clarify wines. The following are the common protein fining agents and their typical uses in wine:

• Gelatin: This compound is the product of hydrolyzed ligament, skin, and tendon tissue from animals. Gelatin is added to white juice to assist clarification and reduce bitter flavors and juice browning. It is sometimes used along with silicon dioxide or grape tannin compounds for better white wine clarification. Gelatin is added to red wines to reduce bitterness and astringency. It can also reduce red wine color. Gelatin is an aggressive fining agent that is wine soluble. If overfined, gelatin can lead to protein hazes.
• Isinglass: This agent is a collagen preparation that comes from the swim bladders of sturgeon fish. Isinglass is used to clarify white wines and reduce bitter or harsh flavors. The resulting wine is usually very clear. Isinglass produces light and fluffy lees that the winemaker must make sure not to disturb when racking or filtering. Excessive fining can cause a protein haze or impart a fishy smell.
• Egg whites: Egg whites are very high in protein and are a very traditional fining agent. They are commonly used to soften overly tannic red wines in barrel or prior to bottling. Many extended maceration wines are given egg white finings.
• Casein: This agent comes in several forms and is the product of proteins precipitated from milk by acids. Casein is typically used to reduce bitter and harsh flavors from white juices, wines, and sherries, as well as reduce browning. It has limited use for clarifying.