©2014 Domenic Carisetti
Cold Stabilization is a process by which a compound formed in wine, called potassium bitartrate (a combination of potassium and tartaric acid) is removed so that it does not crystallize.
Wineries need to stabilize against these crystals because consumers do not tolerate them in wine. There are some exceptions like aged red wines that throw sediment, often as part of a combination that includes tannin and color as well. In those cases, red wine is decanted off the sediment into a carafe. Decanting is a process of slowly pouring the wine off the sediment so as not to disturb the sediment.
The crystalline structure of potassium bitartrate is harmless but it does cause alarm among consumers who mistake it for shards of broken glass in the wine.
The first step in determining if a wine may already be cold stable is to place a filtered sample of the wine in a refrigerator at 40°F for 10 days (most refrigerators are already at that temperature) since that is the average length of time a consumer will keep cold wine before drinking the entire bottle. If the wine throws any kind of crystalline matter, the wine is tartrate unstable.
If the wine is unstable, there are many options available to make the wine stable.
Since tartrate drops out when the wine is chilled, it makes sense to chill the wine, however, that is only one way to make the wine stable. Chilling alone is the most expensive way to stabilize against tartrates if you rely on mechanical chilling and not natural chilling.
These are options I both use and/or recommend to farm wineries to cold stabilize their wines:
- New wines are already supersaturated with tartrates so as soon as fermentation starts or if you chill juice prior to fermentation, tartrates will begin to drop naturally. As you chill a juice, tartaric acid will begin to drop out, raising the pH of the juice. As the pH increases it shifts the equilibrium of the wine from stable to unstable which means that more tartrate will begin to drop out. Not all the tartrate is removed in new juices but at least you get a good head start. There needs to be additional treatment to drop the remaining tartrates to the point of the wine becoming stable. That means that either the level of tartaric acid or the level of potassium or the existing formation of potassium bitartrate (already formed) has to get down to a level where it will not be a problem nor can react to form more tartrate.
- If you live in a cold climate, take advantage of the cold temperatures to store your wine outside in a stainless or food grade plastic tank. It is better to have the wine in tanks under some type of cover to prevent snow or ice from getting on the tank lid. An outside building with at least one open side will do the trick. The least amount of sediment in your wine prior to placing it outside will render the wine more stable. When the wine is outside for 3 weeks at a temperature of 18°F or colder, rack it off the tartrate crystals and bring it inside. Better yet, if you own a filter, then filter it cold as you bring it inside for storage. Filtration removes colloidal structures that form around the bitartrate crystals so the crystals do not re-form in the wine.
- If you absolutely have to chill your wines by refrigeration using glycol or ammonia, your electric bill takes a hit. Keeping wines chilled in the winery for three weeks gets expensive. There is a method by which you can chill a wine and stabilize it in 2 hours called rapid Detartration or the “Contact process”. It requires chilling a wine to 18°F and filtering the wine into a tank. Once the wine is in the tank, pure potassium bitartrate crystals are added at a rate of 15 grams for every gallon of wine to be treated and the wine is kept in constant contact with the bitartrate for a maximum of 2 hours. The wine is then refiltered out of the tank to a new tank. This process was established in Germany by the Seitz Corporation.
- If you do not have refrigeration equipment, you can use a method called calcium tartrate seeding which works on wine at room temperature but does not impart any calcium into the wine. There is a commercial product available on the market called “Koldone” which utilizes this process.
Koldone is a proprietary product (Cellulo Corporation) used to help obtain potassium bitartrate stability. It is produced by mixing calcium carbonate and L(+) tartaric acid in a specific ratio. The addition of Koldone into a wine causes the added calcium carbonate to react with the wines tartaric acid to form an insoluble calcium tartrate. Precipitation is aided by calcium tartrate crystals present in Koldone, which act to seed. Thus, the addition of Koldone to a wine causes it to become super-saturated with respect to calcium tartrate and this is precipitated rapidly from solution. The tartaric acid concentration can be reduced to a low enough level where cold stability is achieved.
- Another method for tartrate stability is ion-exchange where either potassium and/or tartaric acid are exchanged with non-reactive compounds. This principle operates in the same manner as a water softener.
- Yet another method for tartrate stability involves electro dialysis.
Needless to say, tartrate stability achievement in wine is an ongoing aspect of the winemaking process with numerous ways to achieve stability.