Bentonite, Composition and Use in Wine Kits
Bentonite is 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. The process not only improves a wine’s appearance, but also makes sure that
it is stable. This means that it won’t change its appearance, taste, aroma, or chemical composition
while in storage.
Bentonite is a type of clay, known as aluminosilicate, whose technical name is Montmorillonite. It’s
found with various minerals attached to it, such as sodium, calcium and magnesium, and was
originally discovered in Fort Benton, Wyoming (where the name came from). It’s used in
winemaking, beauty treatments, mineral extraction, water treatment, and even in kitty litter.
When used in winemaking, it is stirred into the wine to remove proteins and other haze-causing
particles. It works through adsorption, meaning that it attaches itself to a particle. Together, they
are too heavy to stay in suspension, and fall to the bottom of the carboy, leaving the wine clear and
stable. Bentonite settles out of the wine so completely that it does not leave any residue of taste or
colour behind.
Some wine kit companies (like Winexpert) add their bentonite on the first day, and some add it
after fermentation. You may have noticed that this is one of the fundamental differences between
various types of kits. The reasons behind it go beyond technology, straight into winemaking
philosophy.
When bentonite is added on the first day, it disperses through the wine, and most of it 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 carbon dioxide (CO2) in the wine is
undergoing.
As the yeast ferments the sugar, it converts it into CO2 and alcohol. The bubbles of gas don't simply
appear out of nowhere: they want to come out of suspension on some kind of point, where a
nucleus of gas can form the beginning of a bubble. This process is called 'nucleation'. The point at
which gas bubbles come out of suspension could be a scratch in the carboy, a bit of grape material
– or a particle of bentonite. 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 adsorb other particles 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 at post-fermentation, it does not have the advantage of the
CO2 lift that it would get during fermentation. So it doesn’t recirculate on its own. Therefore the
winemaker is obligated to stir it through the wine repeatedly, to ensure thorough dispersal. In
addition to this, because the bentonite will quickly settle out before it can effectively clear the wine,
significantly more needs to be put in, when it is used post-fermentation instead of earlier on.
This is why Winexpert kits typically use 10 or 15 grams of bentonite, while some companies use up
to 80 grams in their kits. Not only does the larger 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 actually possible to strip a red wine to the point where it becomes 'white'. Too much
fining can lead to a stripping of colour and flavour, making it necessary to formulate much darker
and stronger wine kits to compensate. By adding the bentonite on the first day, we are allowed to
make the formulation much closer to the desired finished wine, without extra additions or
manipulation.
It may seem a little odd to be adding clay to wine, yet the finished product turns out clear and
delicious, polished very nicely by a little bentonite.