Protein stability and bentonite: stopping haze before it starts

A clear white wine that turns cloudy on a warm shelf has thrown a protein haze — heat-unstable grape proteins that unfold and clump when warmed. It is a classic, avoidable fault of whites and rosés, and the standard fix is bentonite, a clay that adsorbs those proteins so they can be removed before bottling.

Why the haze forms

Grapes carry small amounts of heat-sensitive proteins that survive fermentation. In the bottle, warmth during transport or storage makes them denature and aggregate into a visible cloud. Reds are protected by their tannins; whites and rosés are not, which is why protein stability is mainly a white-wine problem.

The heat test tells you the risk

You cannot see instability in a bright wine — you provoke it. Heat a sample (commonly around 80 °C for a set time, then cool) and measure the increase in haze (turbidity, NTU). A wine that clouds significantly is unstable and needs treatment; one that stays clear is stable and needs none — over-fining a stable wine only strips it.

Bentonite is not free of cost to quality: it removes some aroma and colour and leaves lees, so the goal is the minimum dose that passes the heat test, not the maximum that guarantees it.

Bench-trial the dose

• Prepare a properly hydrated bentonite slurry — dry bentonite added straight to wine will not perform.
• Trial a range of doses (typically somewhere from ~20 up to ~100 g/hL depending on the wine) on bench samples.
• Heat-test each trial and pick the lowest dose that comes back stable.
• Account for the volume you will lose as lees when you scale to the tank.

From dose to quantity

Once the trial gives you a dose in g/hL, converting it to the kilograms for a specific tank is simple arithmetic — the same dosing maths as any fining agent.

In GrapeFlow the bentonite addition and the stability test are logged against the lot, so the treatment is traceable and repeatable. Guidelines only — always bench-trial and confirm with your own heat test.