Bentonite is a form of clay that is commonly used as a fining agent in white winemaking to remove dissolved proteins, as these can precipitate out in the wine after bottling, causing the wine to become cloudy and unfit for sale. Unfortunately, bentonite will also remove flavour components, and so should be used sparingly.

It is usually used after fermentation after careful testing to see exactly how much is needed, but some winemakers add it to must at the clarification stage, as it is better to carry out treatments on musts and wines as early as possible in the winemaking process, as they will then have less impact on the final product.
On the other hand, if the wine is going to be aged for any time on its lees, this will reduce the eventual levels of bentonite required.

Often bentonite has to be allowed to swell in water before use (see manufacturer’s instructions).