Skip to content
Cellari The Winemaker's Corner

Winemaking guide · Protein stability

How much bentonite? Protein stability in white and rosé wine

Most white and rosé wines need 10 to 100 g/hL of bentonite, or 0.1 to 1 g/L, and some need none at all. Only a bench trial tells you how much bentonite to add to wine like yours: a few samples at rising doses, a heat test at 80 °C (176 °F), and the lowest dose that stays clear.

By the Cellari team Written with AI assistance Published

Protein haze in wine: from invisible protein to white cloud

Every white wine holds proteins from the grapes. The ones that cause haze belong mostly to two families of defense proteins the vine makes against disease (PR proteins): thaumatin-like proteins (TLPs) and chitinases. They survive fermentation and the wine’s acidity, and you can’t see them.

The trouble starts with heat. The folded protein opens up, its sticky parts are exposed, and it clings to other proteins and to compounds such as phenolics and sulfate. The clumps grow until they scatter light: the wine looks hazy, and sometimes white flakes appear.

  1. Cool cellar Folded protein In a cool cellar the protein is compact and soluble. You can’t see it, and the wine is clear.
  2. Summer, transit, 80 °C Heat opens it up In heat the protein unfolds, and its sticky parts (yellow) are exposed. The wine is still clear.
  3. Sticking together It sticks to others The open proteins bind to each other, to phenolics (green) and to sulfate in the wine.
  4. Cooled: visible haze Visible haze As it cools, the clumps grow and scatter light. The wine is hazy, sometimes with white flakes.
Folded protein Unfolded protein, sticky spot Phenolics Haze particle
How protein haze forms, magnified, following AWRI’s explanation.

This haze can form at any temperature, but it forms faster in heat (AWRI). Above about 65 °C (149 °F) the proteins unfold, so the stability test heats the wine to fast-forward months of storage in bottle.

Which wines get it

The proteins come from the grapes and are already in the juice. In red wine protein haze is rare: tannins bind to the proteins and settle out with them, so almost no unstable protein is left. The exceptions are low-tannin reds, reds from very cool regions, and sometimes Pinot Noir.

In sparkling base wine, the second fermentation in bottle adds alcohol, so some producers add, for example, about 1–1.5% alcohol to the sample before the heat test.

A hot summer is a heat test you didn’t ask for

In a UC Davis trial, eight white wines that had not been fined with bentonite were put into storage. After a month at 35 °C (95 °F), as in a truck or a warehouse in summer, 7 of them turned hazy. Even in closed cases in controlled storage at 13–17 °C (55–63 °F), 6 did. The wines fined with bentonite stayed clear, except one Riesling.

Fruit from warm regions, such as Israel, also often carries more protein (Virginia Tech). A white wine that leaves the winery without a stability test is a bet on the trip to the shop.

What sets the protein level in wine

Wine holds between 10 and 300 mg of protein per liter (Purdue). These are the main factors:

The fix: bentonite fining

Fining means adding something that binds a compound in the wine and settles out with it. Bentonite is a clay built from very thin layers of an aluminum silicate mineral. The layers carry a negative charge, and positive ions such as sodium or calcium sit between them. In water the layers move apart (swelling), and a huge surface area opens up.

At wine pH most proteins carry a positive charge. When they meet bentonite, they take the place of the sodium ions and bind to the layers (ion exchange). The bentonite settles to the bottom with the proteins on it, and you rack the wine off the lees.

  1. + + + + + + Powder Dry powder Thin clay layers, packed tightly together. Sodium ions (yellow) are trapped between them.
  2. − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − + + + Swelling in hot water Water (blue) gets between the layers. They move apart, and their negatively charged surfaces are exposed.
  3. + + + + The proteins bind Positively charged proteins cling to the surfaces and take the place of the sodium.
  4. Stable wine Lees It settles as lees The loaded clay is heavy and sinks. The wine above it is stable, and you rack it off the lees.
How bentonite binds proteins, magnified. For this to work, the bentonite has to swell fully in water before it goes into the wine.

Sodium or calcium bentonite

The bag usually says which ion sits between the layers. That decides how much the bentonite swells, how much protein it takes up and how much wine you lose in the lees.

Sodium bentonite (Na)Calcium bentonite (Ca)
Swelling in water High Low
Protein binding Strong Weaker, often needs more powder
Lees Fluffy and loose, more wine lost when racking Compact, less wine lost
Clarification Good Better
Watch out A heavy treatment can double the wine’s natural sodium, which is low to begin with Not recommended above pH 3.4. Adds calcium and raises the risk of calcium tartrate crystals
For illustration only. In practice, bentonite lees hold 5 to 10 percent of the volume of wine treated.

There is also sodium-activated calcium bentonite, which falls in between. Whichever type you choose, run the trial with exactly the same bentonite, from the same lot, that you will use in the tank. MoreWine notes that one product may need four times as much as another.

Bentonite dosage: the usual range, and why only a trial decides

According to AWRI, trials usually test 0.1 to 1 g/L, or 10 to 100 g/hL. Aromatic, protein-rich wines such as Sauvignon Blanc can need 1–3 g/L (Enartis).

But the dose doesn’t follow from the amount of protein. Here are seven wines tested at AWRI:

In a Pinot Gris with 143 mg/L of protein, 0.2 g/L of bentonite was enough. A Sauvignon Blanc with 133 needed 0.5, two and a half times as much: its higher pH, lower alcohol and phenolics made it more sensitive. Source: AWRI Technical Review 235, the 2-hour test.

Home winemaking forums sometimes say to add a gram per liter and be done with it. For the Chardonnay in the chart that is bentonite it never needed, and for the Riesling five times too much. Extra bentonite strips aroma and flavor, and makes more lees, which means more wine you throw away.

Heat stability test: how to check for protein haze

The method most winemakers use today is AWRI’s:

  1. Filter through 0.45 µm, as before bottling
  2. Measure the starting haze in NTU
  3. Heat in a water bath 80 °C · 2 hours
  4. Cool in water 20 °C · 3 hours
  5. Measure again the change from the start Δ < 2 NTU

NTU is a unit of turbidity. You measure it with a nephelometer (turbidity meter), which checks how much light the sample scatters. Some labs are stricter and ask for a rise of less than 0.5 NTU, but AWRI sees 2.0 as a more reasonable threshold.

Fast cooling makes more haze, so stick to 20 °C (68 °F). If you don’t have a bath at that temperature, one hour in the fridge and two hours at room temperature will do. The old method, 6 hours of heating and a night at 4 °C (39 °F), may overstate the dose (AWRI).

Without a nephelometer

Many wineries check by eye: in a 1998 survey in Australia, 29 of 34 wineries relied on a visual check. To make it work, use identical sealed tubes, an unheated control sample next to them, a dark room and a strong flashlight shining from the side. A rule of thumb: if you can see haze after heating, the wine is not stable.

A tip for home winemakers: a sous-vide cooker in a pot of water holds a steady 80 °C (176 °F) for two hours. Make sure your model reaches that temperature, and seal the tubes well.

Worked example: a 100 mL trial, a 1,500 L tank

A Sauvignon Blanc after fermentation, 1,500 L (about 400 US gallons) in the tank. Make a 5% bentonite slurry (bentonite mixed into water): 5 g of bentonite, made up to 100 mL with water. Take five 100 mL samples of the wine: one is the control, and the other four get slurry at rising doses. Let them settle, filter them and run the heat test. Tap each sample:

Dose in g/hL · slurry added to 100 mL · NTU rise after heating

1.2 mL of slurry in 100 mL of wine is 60 g/hL. A rise of 1.1 NTU: stable. For a 1,500 L tank: 900 g of bentonite. This is the lowest dose that passed.

Stability threshold: a rise of less than 2.0 NTU after heating

The NTU values here are for illustration. Your wine will give different ones.
  • Sauvignon Blanc
  • Volume 1,500 L
  • 100 mL samples
  • 5% slurry
  • Doses 0–80 g/hL
  1. Slurry per sample: 1 mL of a 5% slurry in 100 mL of wine is 500 mg/L, or 50 g/hL. So 0.4, 0.8, 1.2 and 1.6 mL give 20, 40, 60 and 80.
  2. The results: 60 g/hL is the lowest dose that stays under 2.0 NTU.
  3. Bentonite in the sample:
    5 × 1.2 ÷ 100 = 0.06 g
  4. The dose in mg/L:
    0.06 × 1,000,000 ÷ 100 = 600
    which is 60 g/hL.
  5. Bentonite for the tank:
    60 × 1,500 ÷ 100 = 900 g
  6. Or in the same 5% slurry (1.2 mL per 100 mL of wine):
    1.2 × 1,500 ÷ 100 = 18 L

Add 900 g of bentonite

18 L of slurry is 1.2% of the tank volume, and that is a lot of water. The usual rule (Purdue’s, for one) is to add no more than 1% water to the wine, so for the tank make a thicker slurry: about 1 kg per 8 L of water, which is 900 g in about 7.2 L, under half a percent. Keep the water temperature and the swelling time the same as in the trial.

If you are torn between two doses, AWRI recommends the higher one. Here 60 passed with a comfortable margin (1.1 NTU), so there is no reason to go up to 80.

Work it out for your wine. Pick Bentonite as the Product, then enter the Stock solution strength, the Stock added to the sample that passed, the Sample size and the Volume to treat. For this example that is 5%, 1.2 mL, 100 mL and 1,500 L, and it gives 900 g, or 18 L of the same slurry.

Open the bench trial calculator

If you already know the dose in g/hL, the additive dose calculator turns it into grams for any volume.

In the tank: prepare, add, settle, rack

  1. Weigh the bentonite to the calculation, from the same lot you tested in the trial.
  2. Make a slurry. Use hot water, about 60 °C (140 °F), with no chlorine. Sprinkle the powder into the water while stirring hard, not the other way round, so no lumps form. Don’t swell it in wine: there the bentonite never swells all the way.
  3. Let it swell for at least 4 hours, usually overnight. Don’t keep a ready slurry for more than 24 hours. Some products tell you to swell them in cold water.
  4. Add it slowly and stir hard for at least 10–15 minutes. The wine should be above 10 °C (50 °F). Stirring with an inert gas, such as nitrogen, cuts down oxidation.
  5. Let it settle. In a tank this takes about a week, depending on the height of the tank.
  6. Rack off the lees. Tip: let the lees settle again in a small vessel, or filter them, to save more wine. Taste that wine before you return it to the tank.
  7. Test again after every addition and blend. Copper, tannin or blending with another wine can upset a wine that was already stable. Lysozyme, used to block malolactic fermentation, can also haze a white wine, and it is best to leave two weeks between it and the bentonite.

In the juice or in the wine?

You can add bentonite to the juice, before or during fermentation. The upside: much of the aroma is still bound and doesn’t get stripped, and there is less lees to deal with after fermentation. The downside: juice holds more protein, so the bentonite works less well. It also takes up nitrogen and other compounds the yeast needs, and can slow the fermentation or raise H₂S. If you add it to the juice, top up the yeast nutrients.

Even after treating the juice, test the finished wine, and add more if it needs it.

Heat stabilization first, cold stabilization second

  1. Heat stabilization Bentonite against protein haze
  2. Cold stabilization Against tartrate crystals (KHT)
  3. Filtering and bottling After a final check

There are three reasons for this order. Calcium bentonite adds calcium to the wine and raises the risk of calcium tartrate crystals, so test tartrate stability only after fining. Tartrate stabilizers such as CMC, metatartaric acid and polyaspartate can cloud a wine that isn’t protein stable. And in the cold, the tartrate crystals (KHT) pack down the bentonite lees, so you lose less wine when racking.

Tartrate dropping out in the cold also shifts the pH, so Purdue recommends chilling the trial samples too if you plan to cold stabilize. The next step is covered in crystals in wine and cold stabilization.

Work out the sulfite addition before bottling with the guide How much sulfite to add to wine.

Alternatives to bentonite

Common mistakes

Frequently asked questions

What about ready-made test kits?

According to AWRI, Proteotest and Prostab predict a dose close to the 2-hour heat test. Bentotest predicts higher doses, so it can lead to overfining.

How long should the trial samples sit before the heat test?

AWRI gives one to two hours, or overnight, until the wine starts to clear and lees build up at the bottom. Scott Labs recommends at least 24 hours.

What is the difference between g/hL and g/L?

A hectoliter is 100 L. 1 g/L is 100 g/hL, and 1 g/hL is 10 mg/L (ppm). In US gallons, 1 g/hL is about 0.04 g per gallon, so 60 g/hL is about 2.3 g per gallon.

Glossary

Bentonite
A clay that swells in water and binds proteins.
Slurry
Bentonite powder dispersed and swollen in water, before it goes into the wine.
PR proteins
The vine’s defense proteins, including TLPs and chitinases. They cause most protein haze.
NTU
A unit of turbidity, measured with a nephelometer (turbidity meter).
Racking
Moving the clear wine off the lees into another vessel.
Cold stabilization
Chilling the wine so tartrate crystals (KHT) drop out before bottling.

Calculators for this guide

Sources