Fining Agents – Bentonite

A question that seems to come up regularly on home winemaking bulletin boards, newsgroups and faq’s have to do with fining agents. A fining agent is something that is added to the wine at some point before bottling to help it clear.

There are quite a number of differing fining agents – even egg whites believe it or not, may be used to help clear wine. What “clearing” means is to assist in the process of having particulate matter settle out and drop to the bottom of the carboy before bottling. Of course, it is not always necessary to use a fining agent – often ageing will allow a wine to clear on its own.

This article will deal with bentonite – what it is, how it works, and how to use it to fine your wine.

What Is Bentonite?

Bentonite is a special type of clay that was first named in Wyoming in the 19th century. It is distinct from other clays in that bentonite is formed from volcanic ash. It has super water absorption characteristics and some even claim medicinal properties when the clay is consumed or used externally. The same quality that makes it an excellent fining agent is that which those who claim health benefits – bentonite is negatively charged and therefore acts as a magnet, attracting positively charged matter which attaches to the bentonite.

In winemaking, this means that particulate matter in the wine will attach itself to the bentonite and eventually fall to the bottom of the carboy.

Because of bentonite’s absorption qualities, when added to water it can absorb more than 7 times its original dry weight. As it swells, the surface area of bentonite increases enormously as it expands to 18 times it’s volume.

How Bentonite Works In Wine

As noted above, bentonite is a negatively charged substance and when hydrated and added to wine, it will attract the positively charged particulate in the wine. As bentonite hydrates and swells, it becomes like a sponge which accounts for it’s very large surface area. When it is mixed thoroughly into the wine and is dispersed throughout, the positively charged matter in the wine attaches to the bentonite. The weight of the molecules then cause the matter to drop to the bottom of the container and become what is known as “finings.”

There are different preferred methods of when to add bentonite to the wine, and we’ll discuss this in the next section.

Using Bentonite In Your Wine

There are two different schools of thought on when to add bentonite. One school says to add it to the must before you add yeast. The other school of thought suggests that bentonite be added after fermentation has been completed. There is no right or wrong answer, and with your own experimentation, you may end up with your own preference. Regardless of when you add it, the actions of bentonite are the same. However, some believe that there is an additional benefit when adding to the must before fermentation begins.

When added to the must on the first day, it is thought that the bentonite will begin to work immediately, and drop to the bottom with particles attached, within a day or two. However, during the fermentation, large amounts of CO2 are released during the process, and this causes the bentonite to circulate, constantly, attracting more positively charged particles. This means less work for the winemaker than if bentonite is added after the fermentation.

If bentonite is added post fermentation, it will eventually sink to the bottom with some particles, but possibly not all, so when it is added after the completion of fermentation, the wine should be stirred for several days in order to recirculate. For those winemakers that spend some time degassing their wine by stirring or using a device such as a “Fizz-X,” this isn’t an issue, But for those that just want to leave the wine to degass on it’s own, then adding bentonite at the beginning of the winemaking process is probably the best time.

You shouldn’t just add bentonite directly to your wine or must. Instead, you should hydrate it first. This can be a wee bit tricky; if you don’t do it correctly, you’ll just end up with water and a glob of “mud.” I like to use about half a cup of hot water (100 degrees F. or higher), and then very slowly, as I’m stirring the water with a fork or a whisk, pour the bentonite into the water. Stirring vigorously will help to ensure a more uniform mixture of bentonite and water, which can then be poured into your must or wine. Of course, you should stir your wine immediately upon adding the mixture to it.

Bentonite may be added to any type of wine, red or white. It may seem weird at first (like it was to me when I first used a kit that called for adding clay to my wine!) to use bentonite, but don’t worry – with the use of bentonite, you’ll in fact be ensuring less dirt and particulate in your finished wine!

How Much Bentonite?

Although some wine kits come with as much as 80 grams of bentonite, many winemakers believe this is an excessive amount to add to a wine, and could adversely affect the flavour. 10 to 15 grams, or about 3 teaspoons for a 5 (6 US) gallon carboy of wine is probably just fine.

More Bentonite Resources

The Bentonite Cure – No idea if any of the health claims made about bentonite have any basis in truth, but this is interesting.

Hydrated Bentonite – More health information about bentonite.

Wyoming Bentonite – A little history on the use of bentonite in America during the 19th century.

Double Agent Bentonite – An interesting article by Tim Vandergrift, writing for Brew King Limited.

Using Finings To Improve Your Wine – As the title suggests, an article on using fining agents including bentonite.