Cold Stabilization
After your wine has completed primary fermentation (and secondary fermentation if required), and you have stabilized, degassed and used the necessary fining agents, you should now put your wine through a process called cold stabilization. Not everyone uses this step, however, I find using it makes for a much more clear, well balanced wine.
Note: Don't use this step if your TA is low as it will cause your TA (total acidity) to drop)
The purpose behind cold stabilization is to decrease your acid levels by removing all tartrate crystals from a wine during its fermentation stage. Tartrate Crystals are also called "wine diamonds". They are a natural product of the wine, and form when the wine gets too cold.
Tartaric acid is a normal grape acid. Potassium also exists in grapes, and when these two things bind together under cold conditions, they form little potassium bitartrate crystals, which then settle to the bottom of the bottle. They're completely harmless, and quite natural. The problem, of course, is with appearances.
While in Europe these crystals are accepted as a sign that the wine is a natural one, and even appreciated, North Americans are used to wine being clear, pure, filtered, processed and de-sedimented. Consumers often panic when they see little crystals in their Chardonnay, thinking they are impurities or even bits of broken glass. Cold Stabilization is a way to prevent these crystals from forming.
In order to cold stabilize your wine you will need a place where the temperature is around 0 - (-2) degrees Celsius. (This may be found in your cold cellar during winter months or, if you’re lucky enough an empty fridge). Place your carboy into this area and wait for 2 to 3 weeks. During this time the compounds will bind and the tartaric acid will crystallize and precipitate to the bottom of the carboy.
You will also likely find that within this time span the wine should have settled out quite a bit. If you added in your fining agents prior to this step, you will notice that a lot of the sediment will have begun to settle the bottom of the carboy. As cold stabilization takes place, the potassium bitartrate crystals will settle at the same time and help to compact the layer of sediment (lees) at the bottom - making you save more wine when it comes to your next racking.
After 2 to 3 weeks once you can see that the wine is both clear and there is a thick layer of sediment on the bottom of the carboy accompanied by small crytals, you are now ready to move on to the next stage. Putting your wine through cold stabilization should drop the TA (total acidity) of your wine by .5 - 1 point. (or .5 - 1 grams of tartaric acid / 100 ml of wine)
Note: If you do not have the facilities to process the cold stabilization phase, don’t worry about it. As mentioned before, this process is only making your wine more presentable, and not better tasting.