Bentonite is a common additive used to clarify and fine wines. It’s great for removing protein haze and can be used to remove off aromas.
Bentonite is a unique clarifier in that it is the only one that may be used during fermentation as well as afterward. When you add bentonite at the beginning of fermentation you’re relying on the carbon dioxide bubbles that form to carry the bentonite up through the wine and, when the bubble pops, let it fall back down to the bottom. These repeated trips to up and down through the wine allow the bentonite to clear the wine as it’s being made.