Fining is the name given to an important part of the clarification phase of wine making. Wine is supposed to be very clear and completely free of any suspended particles, so wine makers go to great lengths to clarify it.
Wineries use industrial filtration machines and special chemical additives to help precipitate out any suspended solids, no matter how small. They also let the wines sit still for very long periods so they can rack out the solids that have fallen to the bottom. That is, they can siphon off the good stuff from the top, leaving the bad sludge at the bottom of the carboy.
The unobvious part of all this is fining. Careful and patient filtering will remove most of solids. However, did you ever notice that liqueurs, which have aged for many months undisturbed, can have a fine mist at the bottom. Fining ensures this does not happen with wine. It is a process where chemical substances are added to attract the solids and proteins, whereby they form a clump that falls to the bottom. These fining substances have a specific gravity that is slightly greater than the wine. As the substances sink through the wine it binds with any remaining unwanted particles that are suspended in the wine and precipitates them to the bottom, leaving the wine free of any cloudiness.
Historically, a wide variety of agents have been used for fining: ox blood, egg whites, milk casein, fish bladders, horse gelatins, seaweed, clay, and others. In fact, almost any protein will work at least somewhat, by binding to other proteins and forming solid deposits.
In modern enology, there are organic and inorganic fining agents. Some work electrochemically, with the agent having a positive charge attracting negatively charged particles such as grape tannin. Many of the commercial varieties, like Claro K. C. and Sparkolloid, are mixtures of both organic and inorganic materials. Of the pure inorganic, Bentonite is probably the best known. It is an aluminum silicate clay from Wyoming, which is apparently quite popular among Californian wineries. Many fining agents need to be filtered out themselves using a very fine filter, which may present more problems. However, a good winemaking supply store will be able to tell you a lot more about these substances and help with product selection.
Contributor: WineDefintions Staff Writer