Bentonite as a fining agent
Bentonite is, indeed, a fining agent. Fining is the action of removing particles that make a haze in wine by combining them with materials that bind to them and force them out of suspension, leaving the wine clear and bright. It not only improves a wine’s appearance; it also makes sure that it is stable. Stable means that it won’t change appearance, taste, aroma, or chemical composition while in storage.
Bentonite is stirred into the wine to remove proteins and other haze causing particles. It works through absorption. This means that it attaches itself to a particle, and together they are too heavy to stay in suspension, falling to the bottom of the carboy, leaving the wine clear and stable. Bentonite settles out so completely that it does not leave any residual taste or color behind.
What is the advantage of adding it to my wine on the first day?
Midwest suggests that you add bentonite on the first day. The reasons behind it go beyond technology, straight into Wine Making philosophy. When bentonite is added on the first day, it disperses through the wine and most settles to the bottom within a few hours. At the end of 48 hours, however, the bentonite is back in circulation. This is because of the process of gas nucleation that the CO2 in the wine is undergoing.
As the yeast ferments the sugar, it converts it into carbon dioxide (CO2) and alcohol. The bubbles of gas don’t actually appear out of nowhere. They want to come out of suspension on some kind of a point, where a nucleus of gas can form the beginning of a bubble. The bentonite is surrounded by a bubble of gas and floats up to the surface of the wine. When the bubble bursts, the particle of bentonite drops back down to the bottom of the carboy, all the time working to absorb the particles that are clouding the wine. In this way, the bentonite is circulated around the wine continuously for days, doing its job.
When bentonite is added to a wine kit post-fermentation, it does not have the advantage of the CO2 lift that it would get during fermentation. Therefore the winemaker is obligated to stir it through the wine repeatedly, ensuring the thorough dispersal. In addition, because the bentonite will quickly settle out before it can effectively clear the wine, significantly more is needed when used post-fermentation. RJS Craft Winemaking kits typically use 10 or 15 grams of bentonite. Some other companies use up to 80 grams! This is far too much. Not only does this amount cause the formation of a deep, loose sediment bed; it also has the effect of stripping the wine.
Finings are considerably more powerful than most people suspect. With a sufficient dosage of finings it is possible to strip a red wine to the point where it becomes ‘white’. Too much finings can lead to a stripping of color and flavor, making it necessary to formulate much darker and stronger wine kits to compensate. By adding the bentonite on the first day, the formulation can be much closer to the desired finished wine, without extra additions or manipulation. Although it may seem a little odd to be adding clay to your wine, when the finished product is clear and delicious, you’ll be glad that there was a little bentonite to polish it up.
Read this article for more info on Bentonite.