Now that harvest of grapes is finished and the wines have been fermented, we begin to clarify and stabilize the wines. Clarification is done primarily by settling and racking (pumping cleared wine after it rests in a tank for approximately 3 to 4 weeks to an empty tank) and by filtration by pumping wine through filter pads at low pressure to remove particulate matter.
Stabilization for grape wines primarily involves removing “tartrates”, chemically known as potassium bitartrate. Wines which have not been cold stabilized may precipitate tartrates or “argols” in the bottle, harmless enough, but gritty. They are NOT sand, broken glass, or sugar. People consider them unsightly.
If you have visited the winery during the November Wine Trails, you may have seen our chiller tanks in operation during the process of cold stabilization with layers of ice on the tanks’ exteriors. The naturally occurring fruit acid in a grape is primarily composed of tartaric acid, the counterpart of malic acid in apples, pears & cherries; and the counterpart of citric acid in lemons, oranges, strawberries, blueberries & blackberries. While malic and citric acids are not cold sensitive, tartaric acid in grapes is cold sensitive: it forms crystals when chilled excessively. So, all of our grape wines are chilled in the winery to at least 30° Fahrenheit in our cold stabilization tanks to remove excess tartrates. As the ice forms on the tank exterior, the tartrates form a sandpaper-like layer on the tank interior. Tartrates, incidentally, are commonly known as cream of tartar, the same ingredient used in baking. Below 27°F, ice forms:
The recommended minimum “cold” service temperature for white wines, rosé wines, and blended red grape wines (Logan’s Blue, Blackberry Nights, Sangrias) is 38°F. If you chill wine much lower than this by say, putting a bottle of wine in a freezer, you risk not only freezing the wine out of the bottle, making a mess, and possibly breaking the bottle, but also precipitating more “wine diamonds” or tartrate crystals. So, no lower than 38°F, please.
So, keep it cool, but not too icy! Enjoy a glass of Logan’s View wine in good health.