Bentonite is a type of very fine clay made of aluminium-silicate. It is distinct from other clays in that it is formed from volcanic ash. Bentonite is principally used to remove proteins from white wine and juice, as it is a negatively charged clay colloid and reacts with positively charged proteins, precipitating them from the wine. Use of bentonite in red wines should be limited because of its ability to reduce colour by adsorption of anthocyanins.
Mix 3 tablespoons of Bentonite to 500ml of boiling water. It is then recommended that you add 1 to 2 tablespoons of the slurry mix to each 5 litres of wine that is to be treated.