a purified natural clay that is used in fining white wines for the purpose of correcting heat instability. When stirred into a white wine, the Bentonite particles quickly glom onto the larger molecules of protein in the wine, collecting them as the Bentonite settles to the bottom of the wine tank. Later, the act of removing the Bentonite from the tank by racking or filtration removes the excessive protein from the wine. It was these larger proteins in the wine that had caused heat instability, so Bentonite treatment corrects the original heat instability of the wine. Bentonite is never used for red wines because the red pigments of wine tend to stick to the Bentonite also. Heavy Bentonite use in red wine would effectively destroy the red color of the wine. richardgrantwine.com