Can you use bentonite before fermentation, or must it be used after fermentation? This source says you can use it before pitching yeast. https://winemakersacademy.com/bentonite-clarify-wine/
Some kit manufacturers (such as Winexpert) have you add bentonite in the very beginning of the wine making process, right before the yeast. That is so the bentonite will start clarifying the wine as it’s fermented. This is one of the only fining/clearing agents that can be added pre-fermentation.
It sits on the bottom of the fermenter and as carbon dioxide bubbles form during fermentation the bentonite is carried up to the free surface. Along the way it collects positively charged particles. When the bubble reaches the surface and pops the bentonite falls back down to the bottom collecting more particles along the way.
Thus your wine is clarifying during the entire fermentation process.
This source says it must be after. https://eckraus.com/wine-making-bentonite/
It should also be noted here that the Bentonite should not be added to the wine until the fermentation is complete.