Bentonite is one of the only fining agents that can be added pre-fermentation. When the turbulence of fermentation begins, Co2 bubbles form in the must and grab onto the Bentonite lifting it up to the top of the fermenting must. As the Bentonite moves up through the fermenting must, it attracts positively charged solids as it rises. When the Co2 bubbles reach the surface of the fermenting must they will burst causing the Bentonite to fall to the bottom of the fermentation vessel collecting dead yeast and positively charged particles along the way. By the time you are ready to rack from the primary, the Bentonite will have gathered a nice sediment of unwanted solids on the bottom. In addition, Bentonite helps keep wine stable during fermentation. Because your wine is clarifying during the entire fermentation process, when adding the final clarifier before bottling, it will clear much more quickly.