Cold stabilization
Q: I’ve read a bit about cold stabilization for white wines, but I’m not sure I really understand what’s required. Some friends tell me just to put my carboy in the garage over the winter, others say it has to be a lot colder than that. Is there a reliable way for a home winemaker to achieve cold stability, or should I even bother?
A: Cold stability is one of those topics that sounds simple on the surface but gets tricky once you look at the details. What we’re trying to prevent is the formation of tartrate crystals — little “wine diamonds” that can fall out in the bottle or even form on a cork if a wine gets chilled later on. They’re harmless, but consumers often confuse them with glass shards, so most commercial white wines are cold stabilized before bottling.
True cold stabilization requires dropping the wine to around 27–30 °F (-1 to -3 °C) for one to three weeks, depending on the chemistry of the lot. That consistent low temperature allows potassium bitartrate (cream of tartar) to precipitate out in the tank, after which the wine can be racked off the crystals and bottled with confidence. In a commercial winery, jacketed stainless tanks and glycol chillers make this possible. At home, however, it’s difficult to hold wine at those precise temperatures for long enough. A chilly garage might get you partway there, but unless you can verify the temperature and keep it steady, the results are usually incomplete.
Luckily, there is another option. Carboxymethylcellulose (CMC) is a safe and approved cellulose derivative that can be added to white wines to prevent crystal formation. Instead of forcing the crystals to fall out ahead of time, it interferes with their ability to grow large enough to be visible. CMC is odorless, flavorless, and stable, and it’s widely used in the industry as a finishing step for white wines. Do note, however, that it should not be used in reds or rosés — pigments and phenolics can react with it, leading to haze or instability.
For a home winemaker, CMC is often the best route. It spares you the challenge of precise chilling and gives you a stable, crystal-free white wine ready for bottling. Just be sure to follow product directions for dosage and mixing, and you’ll have a clean, clear wine without the worry of diamonds glinting at the bottom of the bottle.
