Cold Stabilization and Tartrate Management

Problem Definition

Potassium bitartrate (cream of tartar) and calcium tartrate are naturally supersaturated in wine and will crystallize when exposed to cold temperatures. While harmless, tartrate crystals precipitating in bottle create consumer complaints and perception of quality problems. Ensuring tartrate stability before bottling is a standard quality control requirement for most wine styles.

The problem is compounded by:

High initial tartrate concentrations (especially in white wines)
Elevated potassium from certain soils or grape maturity
Calcium from fining agents or water sources
Consumer expectation of “clean” wine

Technical Context

Tartrate Chemistry

Potassium bitartrate (KHT):

Solubility decreases with decreasing temperature
Solubility decreases with increasing alcohol concentration
Forms crystals resembling glass shards or sand

Calcium tartrate (CaT):

Less affected by temperature than KHT
Crystallizes more slowly
May precipitate months after KHT is stable

Saturation and supersaturation: Wine is typically supersaturated with respect to tartrates at cellar temperature. Supersaturation is metastable—wine remains clear until nucleation triggers crystallization.

Nucleation factors:

Cold temperature
Vibration or movement
Addition of seed crystals
Time

Solubility Parameters

Temperature	KHT Solubility (approx.)
20°C	3.8 g/L
10°C	2.8 g/L
0°C	2.0 g/L
-4°C	1.5 g/L

Solubility also depends on alcohol level, pH, and ionic strength.

Saturation temperature concept: The saturation temperature (Tsat) is the temperature at which wine becomes saturated with KHT. Below Tsat, crystallization is thermodynamically favored. Typical Tsat values range from 10-20°C; wines must be stable below consumer refrigeration temperature (~4°C).

Options and Interventions

Cold Stabilization (Traditional)

Protocol:

Cool wine to target temperature: -4°C for standard wines; colder for high-alcohol wines
Maintain for duration: 7-21 days typical
Optionally add seed crystals (4 g/L KHT) to accelerate nucleation
Filter cold to remove precipitated crystals
Test stability before bottling

Miniaturized stability test:

Chill sample to -4°C for 24 hours
Observe for crystal formation
If crystals form, continue treatment
Conductivity test provides quantitative assessment

Energy and time requirements:

Significant refrigeration energy required
Tank occupancy 2-3 weeks
Scales poorly for large volumes

Electrodialysis

Principle: Ion-selective membranes remove K⁺ (and other cations) under electric field, reducing supersaturation without chilling.

Advantages:

No refrigeration required
Continuous process; rapid treatment
Precise control of ion removal
OIV approved; legal in EU

Limitations:

Equipment capital cost
Removes tartaric acid along with potassium
May require acid adjustment post-treatment
Not available for small producers

Additive-Based Stabilization

Metatartaric acid:

Inhibits crystal growth (kinetic stabilization)
Addition: 100 mg/L
Temporary effect: Hydrolysis over 12-24 months reduces efficacy
Suitable for wines consumed young

Carboxymethylcellulose (CMC):

Colloidal protective inhibitor
Effective for KHT inhibition in white and rosé wines
Dosage: 40-100 mg/L
OIV maximum: 100 mg/L
Not suitable for red wines (protein-tannin interaction causes haze)

Mannoproteins (yeast cell wall extract):

Inhibit both KHT and CaT nucleation
Dosage: 150-300 mg/L
Natural product; good consumer perception
Variable efficacy depending on source

Potassium polyaspartate (KPA):

Newer additive; OIV approved
Effective for KHT; some effect on CaT
Dosage: 50-100 mg/L
Suitable for red wines (CMC alternative)

Contact Process (Accelerated Cold Stabilization)

Principle: Addition of fine KHT crystals (4-5 g/L) provides nucleation sites, accelerating crystallization.

Protocol:

Chill wine to -4°C
Add KHT crystite (fine crystals)
Stir continuously for 2-4 hours
Filter cold

Advantages:

Reduces treatment time from weeks to hours
Tank turnover improved
Energy savings vs. static cold stabilization

Limitations:

Requires filtration capacity
Crystal preparation/sourcing needed

Trade-offs and Risks

Cold stabilization:

Energy-intensive
May strip aromatics (cold precipitation of some volatiles)
Time-consuming
Weather-dependent in traditional cellars

Electrodialysis:

High capital cost
Removes desired ions along with potassium
Requires trained operation

CMC:

Protein-reactive: Cannot be used with unfined red wines
Long-term stability uncertain in some matrices
Consumer perception variable

Metatartaric acid:

Temporary protection only
Degrades faster at high temperature
Not suitable for age-worthy wines

KPA:

Newer additive; less track record
Cost higher than CMC
Regulatory status varies by jurisdiction

Calcium Tartrate Consideration

CaT stability is often overlooked. High-calcium wines (from CaCO₃ deacidification, calcium bentonite, or hard water) may precipitate CaT months after bottling even if KHT-stable.

Prevention:

Avoid unnecessary calcium additions
Use potassium bicarbonate for deacidification
Extended cold stabilization (CaT slower to precipitate)
Mannoproteins inhibit CaT as well as KHT

Practical Implications

Variety-specific considerations:

Riesling: High tartaric acid content requires thorough stabilization. Mosel producers may accept some tartrate risk in high-acid wines. Residual sugar wines require careful CMC dosing (may affect perception).
Chardonnay: Chablis AOC stainless-steel styles cold-stabilize routinely. Barrel-fermented wines may have naturally lower tartrate due to lees contact (mannoproteins).
Grüner Veltliner: Wachau DAC wines often bottled early; cold stabilization standard for export markets.

Appellation-specific implications:

Champagne AOC: Base wines must be tartrate-stable before tirage. Cold stabilization standard. Tartrate crystals in bottle after disgorgement would be commercial disaster.
Mosel: Traditional producers may accept tartrate precipitation as natural; export wines stabilized. Contact process increasingly common.
Chablis AOC: Clean, precise style requires stable wines. Cold stabilization routine; CMC gaining acceptance.

Quality vs. stability trade-off: Some producers argue cold stabilization strips wine character. Alternatives (CMC, mannoproteins) may be preferable for aromatic whites. Consumer education about harmless tartrate crystals remains limited.

References

Ribéreau-Gayon, P., Glories, Y., Maujean, A., & Dubourdieu, D. (2006). Handbook of Enology, Volume 2: The Chemistry of Wine Stabilization and Treatments (2nd ed.). Wiley. Publisher Link
Bosso, A., Salmaso, D., De Faveri, E., & Guaita, M. (2010). “The Use of Carboxymethylcellulose for the Tartaric Stabilization of White Wines.” American Journal of Enology and Viticulture, 61(1), 20-28. DOI: 10.5344/ajev.2010.61.1.20
Gerbaud, V., Gabas, N., Blouin, J., & Crachereau, J.C. (1997). “Study of Wine Tartaric Acid Salt Stabilization by Addition of Carboxymethylcellulose (CMC).” American Journal of Enology and Viticulture, 48(4), 419-424. AJEV Link
OIV. (2021). International Oenological Codex. Organisation Internationale de la Vigne et du Vin. https://www.oiv.int/