Using Bentonite in Winemaking

Bentonite is commonly used in winemaking as a fining agent, and it works well, precipitating particles that make wine cloudy in a matter of days (or even hours). Bentonite also removes protein haze from wines, and is commonly added to wine kits (especially white kits) for that purpose.

This post describes my most recent usage of bentonite and what I learned from it.

What is bentonite?

Bentonite is a fine clay formed from volcanic ash. It is negatively charged and attracts positively charged proteins, precipitating them from wine. It is most commonly used in white wines, but not in red wines as it absorbs anthocyanins, which are red, blue, purple, & black pigment particles commonly found in red, purple, and blue vegetables and fruits — this strips color from red wines.

How is it used?

Kit instructions typically state to stir it into hot water. Instructions from one of the leading kit vendors read:

Pour 2 L (8 cups) of hot tap water into bottom of the primary fermenter and stir in Bentonite. Mix well. It is normal for Bentonite to not fully dissolve in water.

Kits add bentonite prior to fermentation, as it speeds up the clearing process, and I suspect that the method of preparing the bentonite prior to reconstitution of the juice/concentrate is far easier. Beginners want things to be easy, and spending time making a bentonite slurry doesn’t fit that model.

Note that bentonite clumps easily and those clumps are stubbornly difficult to break up. I learned to gently pour the bentonite into the hot water while stirring

I decided to add bentonite to my 2023 Vidal wines. I made one batch from juice (pressed the grapes and fermented only the juice), which I refer to as Vidal Juice. The remainder (juice and pulp) was fermented like a red wine, on the skins. I refer to this one as Vidal Orange, as the wine has an orange cast due to pigment leached from the skins.

Formulation

However, being dissatisfied with my usage of bentonite in the past, I researched the topic and read a lot of pages. Like most things in winemaking, there is a lot of diversity and outright disagreement, which include:

• Amount of bentonite to use, which ranged from 1/2 tsp in 1/2 cup water to 2 Tbsp in 1/2 cup water; this is for 19-23 liters of wine.
• Temperature of the water, which ranged from 120 F to boiling the mixture.
• Time to let the mixture rest before adding to wine, which ranged from 1 minute to 48 hours.

Decisions, decisions, decisions …

I thought about everything I read and made the following decisions:

2 tsp in 1/2 cup water. The package said 2 tsp in 1/2 cup, and numerous sites agree with it. Generally manufacturers know how to use their own product, so it made sense.

temperature 160 F (71 C). After reading through many pages, 14o F (60 F) to 150 F (65 C) made sense. When I was heating the water, I mistakenly reach 160 F, so I went with it. In the future, anything between 140 F and 160 F should be good as there is no magic number that is perfect.

time 4 hours. This simply seemed like a good middle ground, and the slurry was in a good condition at this point.

One of the pages I read is the Australian Wine Research Institute’s page on Fining Agents, specifically bentonite. Their method calls for 5 g (1 tsp) bentonite in 85 ml (2.9 oz) water at 60 F (140F). This is 50% more water than I used (4 oz vs 5.8 oz) and based upon my experience (detailed below), in the future I’ll use 3/4 cup water instead of 1/2 cup.

I like the AWRI site because for a research institute, its papers are more easily understandable by people who do not have a Masters or PhD in grape research and/or biochemistry. This doesn’t mean I don’t have to look things up; just that I get the feeling they have less researchers who are using as many buzzwords as possible to impress themselves and their competitors.

Preparation

Once the slurry is made, there is disagreement in how much to use. A common choice is to make up 1/2 cup slurry and add the entire batch to 19 to 23 liters of wine. This made sense, and since I have roughly 12 gallons of wine (pre-clearing), I made a double batch, e.g., 4 tsp bentonite in 1 cup water. This dosage is a bit less than the recommendation, but based upon experience with various fining agents, it should do the job.

I heated 1 cup water to 160 F and put it in a metal bowl. I sprinkled in 4 tsp bentonite and started stirring with a large plastic spoon (one designed for Teflon pans). Since I did not pour carefully, I had a lot of clumps, and used the back of the spoon to crush them. I had to use my finger to scrape off the back of the spoon several times. This took about 5 minutes and I finally decided to just let it rest with a towel over it to keep the heat and humidity in.

Note: Before doing anything in winemaking, observe basic hygiene, which includes washing hands.

Ten minutes later I stirred again. The bentonite had absorbed water and half of it was a smooth slurry. Stirring and crushing clumps for a minute or so improved it.

I let the mixture rest 10 minutes, then stirred again. I repeated this another 3 times and the result was a smooth slurry.

If I had poured the bentonite gently while stirring, I would have made less work for myself.

After that, I let the slurry rest for 3 hours with a towel over the bowl.

Dosage

This is yet another point of controversy, how much of the slurry to use? Most of the pages I read said to use the entire batch (2 tsp in 1/2 cup water) in 19 to 23 liters of wine, while others said to use as little as 1 Tbsp.

I have 3 carboys, each with about 4 gallons in them, so I decided to divide the batch in 3 parts, dividing it equally. I measured by Tbsp, so I’d know how much I was adding to each, for future reference.

The result was 4 Tbsp, e.g., roughly 1 Tbsp per gallon. There was a bit left over, which I didn’t bother with.

Next I used a drill-mounted stirring rod to mix each wine, stirring up any existing sediment (it dropped once, it will drop again), and degassing the wine in the process.

Results

A heavy layer of sediment dropped in all 3 carboys in a matter of hours.

After 3 days I racked the Vidal Juice and moved it into three 4 liter jugs and one 1.5 liter bottle. This wine went into a refrigerator as part of an experiment in cold stabilization. A few days later there is a thin layer of sediment on the bottom of each jug, indicating the bentonite did most of its job within a few days.

I will rack the other carboys soon.

Overall, I’m pleased with the method I used, and will use it in the future.