The following article first appeared in the April 1998 issue of our print newsletter, the Trillium Ridge Times. As this phenomenon occurs once in a while, we thought this would be very appropriate and informative to post here again.
They may look like snowflakes or little lumps at the bottom of the bottle. These crystals are mostly potassium bitartrate, also known as “cream of tartar” in a cookbook. They form from potassium ions and tartaric acid that are both naturally present in grapes, hence in wine.
A very small portion could be calcium tartrate, similar to potassium bitartrate but the only difference is that this is a calcium compound rather than potassium. Calcium is also a natural constituent of grapes and wine.They may be large or small in size. They may form a thin disc at the bottom or just a few crystals you barely see. They are usually transparent white crystals but in wine they may be ivory, brown, red or purple by picking up the pigments in wine.
When wine gets chilled, the solubility of these tartrate salts decreases so the crystals form and precipitate to the bottom. In the wine making process we intentionally try to do it in the bulk containers. It is called “cold stabilization” or we say that “we cold stabilize” the wine. Since the procedure removes a portion of tartaric acid, the main acid existing in wine, the wine becomes less acidic and milder in taste afterwards.
Many small-scale wineries like us rely on the cold temperature during winter to chill down the wine, where larger wineries would use refrigeration systems. Thus we can get into a little trouble when we have a mild winter like these past two years. Our cellar does not get cold enough for the wine to stabilize naturally. What could possibly happen later is that the bottle of wine decides to undergo the cold stabilization all by itself — when the bottle is put in your refrigerator to be chilled and you get surprised at the crystals in the bottle.
For the most part the crystallization process is temperature dependent; that is, it takes place when the wine is chilled as just mentioned. However, it also has a small factor that it depends on time. For example, you may eventually find a small amount of crystals in the bottle that you have been keeping in your cool wine cellar for an extended period of time, usually an order of a year or more.
Both potassium bitartrate and calcium tartrate are quite harmless to your health. When you find the crystals in your wine, all you need to do is to decant the wine away from them and enjoy! If our wine has produced excessive amount of crystals and you can’t feel very comfortable, please tell us about it. We will be glad to exchange or refund, whichever you would prefer.