Cold Stabilisation: Preventing Tartrate Crystals in Bottle

Opening a bottle of white wine to find crystals clinging to the bottom of the cork or resting in the wine is alarming for consumers who don't know what they're looking at. These are tartrate crystals — potassium hydrogen tartrate, also called cream of tartar — and they are completely harmless. But preventing them from forming in the bottle requires cold stabilisation.

What Tartrate Crystals Are

Tartaric acid is the primary acid in wine. Under cool conditions, potassium ions (abundant in wine) bind with hydrogen tartrate ions to form potassium hydrogen tartrate (KHT), which precipitates out of solution as visible crystals. These look like:

Clear or white crystals on the bottom of the bottle
Crystals stuck to the bottom of the cork
A fine crystalline sediment in white wine

They are not glass, not harmful, not a sign of spoilage. But consumer perception is poor, and commercial wine is routinely cold-stabilised to prevent them.

Red wines also produce tartrates but the colour and heavier sediment mask them. The issue is primarily perceived in white and rosé wines.

Conditions that Increase Tartrate Risk

High tartaric acid content: cool-climate wines and wines that haven't undergone MLF (which reduces TA)
High potassium: warm-climate grapes tend to accumulate more potassium
High alcohol: alcohol reduces tartrate solubility
Cold storage: when the consumer stores the bottle in a cold fridge, any unstabilised wine may form crystals

Cold Stabilisation: The Classic Method

How it works

Chill the wine to near-freezing (−3 to −4°C, as low as the wine can go without freezing — wine freezes below 0°C due to alcohol) for 1–2 weeks. At this temperature, KHT solubility drops dramatically and the crystals precipitate out of solution. Once they've settled, rack the wine off the crystal sediment into a new vessel.

The wine is now stable — it won't form further significant tartrate deposits when the consumer chills it.

Practical application

At commercial scale: jacketed tanks with cooling systems maintain near-freezing temperatures precisely. At home:

Move the vessel to a cold room or unheated garage in winter (must reach consistently below 4°C)
Use a chest freezer with a temperature controller set to −2°C and a probe in the wine
Wine in a carboy in a chest freezer: cover with insulation on the sides; only expose the top — keeps temperature more stable

Duration: 2 weeks at −2 to −3°C is sufficient for most wines. Longer is better; shorter risks incomplete stabilisation.

Racking after cold stabilisation

After the cold period, the wine must be racked off the tartrate crystals before it warms back up — the crystals dissolve again as temperature rises. Rack while still cold.

Testing for Tartrate Stability

The mini-cold test: take a 10mL sample of wine, chill to −4°C for 1–2 hours. If no crystals form, the wine is cold-stable. If crystals appear, cold stabilisation is needed.

For commercial producers, a conductivity test (measuring the drop in electrical conductivity as KHT precipitates) is a more accurate and faster stability test.

Alternative Treatments

Metatartaric acid

A polymerised form of tartaric acid that inhibits KHT crystal nucleation. A single addition of 100 mg/L prevents crystal formation for approximately 12–18 months. Simple and cheap — but temporary. After the metatartaric acid hydrolyses (which happens faster in warm storage), tartrate instability returns. Suitable only for wines expected to be drunk within the treatment period.

CMC (Carboxymethylcellulose)

An EU-approved (since 2009) colloid that inhibits tartrate crystal growth more durably than metatartaric acid. Approved for white and rosé wines only. Dose: 100 mg/L. Works well for wines that will be stored long-term. Not approved in all export markets (check USA rules before exporting).

Mannoproteins from yeast

Some commercial preparations of mannoproteins (a yeast cell wall polysaccharide) also provide tartrate stabilisation, with the additional benefit of enhancing texture. Permitted in EU winemaking.

When Cold Stabilisation Is Necessary

Wine type	Cold stabilisation needed?
White and rosé wine for commercial sale	Yes — consumer expectation
White wine for gifts and personal consumption	Recommended — educate recipients about crystals if not stabilising
Red wine	Less critical — crystals less visible, but can be done
High-acid, cool-climate white	Especially important — high tartrate content

What If Crystals Have Already Formed in Bottle?

If tartrate crystals are already in a finished bottle, they are harmless. Options:

Decant through a fine strainer before serving
Let settle, pour carefully, avoid the last cm of wine
No quality impact — it's still good wine

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Tip: A simple way to remember: tartrate crystals are just cream of tartar — the same substance used in baking. When your grandmother's meringue recipe calls for cream of tartar, she's using the same compound that crystallises in your Riesling.