Bentonite
Bentonite is a clay which, in very pure form, is used to fine wines, especially white wines for the purpose of correcting heat instability. When stirred into a wine, the bentonite absorbs excessive yeast protein from the wine and holds it tightly. Under some conditions, this protein could later cause a cloud, haze or sediment to form in the wine if not removed. After allowing the bentonite to contact the wine, it is racked or filtered off, taking the protein with it and ridding the wine of the future problem. The wine is said to have been "bentonite fined."