Have you ever opened a bottle of red wine and found crystals (also known as wine diamonds) on the cork or in the wine itself? I have, and so I decided to do some research to find out what that was all about. My research led me to a lot of great information about cold stabilization of wine. I will share some of what I learned here.
According to wineintro.com, “Some aspects of the wine community are strictly about appearance… It is in this vein that the process of cold stabilization was born – a superficial process whose sole purpose is to make a wine ‘look’ better. The purpose behind cold stabilization is to remove all tartrate crystals from a wine during its fermentation stage… They are a natural product of the wine, and form when the wine gets too cold. It is in essence cream of tartar, forming because of the temperature change. Think of sugar turning into rock candy and you’ll have a good mental image.”
WineMakersAcademy.com continues with the story by saying that “Tartaric acid is naturally present in wine-making grapes, so we can expect all grape wines to have it. However, after fermentation some wines will be supersaturated with tartaric acid, meaning that there is more tartaric acid in solution than what wine can naturally sustain.” In cold conditions, this tartaric acid combines with the potassium that is also in the grape to form potassium bitartrate crystals.
WinesandVines.com finishes up with the down sides of cold stabilization. “Bulk chilling [which is what you do during cold stabilization] has several drawbacks… At the most basic level, cold stabilization involves a loss of wine—as much as 5% of the volume; as in any kind of fining, the gunk removed by the process swims in a bit of perfectly good wine at the bottom of the tank, which gets chucked out, too. The cost of lost wine, however, pales in comparison with the cost of the electricity devoured in holding wine at a freezing temperature for a couple weeks…
“Of increasing importance as world wine standards rise are the ways in which cold stabilization can affect wine quality. By forcing a portion of a wine’s tartaric acid to engage in crystal formation and subsequently drop out of solution, chilling can, to varying degrees, lower acidity and raise pH. This not only changes the wine’s chemical balance but its sensory balance (its perceived acidity) as well. There is both anecdotal and research evidence that the expunged crystals take other things with them, from aromatic compounds to pigment. Finally, holding wine for extended periods at borderline freezing temperatures increases the chances of oxidation, since oxygen dissolves into solution much more easily at colder temperatures.
“All in all, cold stabilization through bulk chilling is a very blunt instrument, exchanging at least some level of loss in wine quality for the removal of a purely cosmetic problem.
“Sooner or later, somebody was bound to build a better tartrate trap, and the past half-dozen years have produced several alternatives. Rather than treating the formation of tartrate crystals as an unavoidable problem better dealt with sooner than later, the new approaches strive to keep the precipitation-grade crystals from forming or growing in the first place, which means less stuff has to be taken out of the wine in order to achieve stability—more technology, more natural wine.”
If you open a bottle that has crystals, stand the bottle upright for a few hours to allow the sediment to settle into the bottom of the glass. Then decant the glass into another container, being careful not to let the sediment go into the decanter. The crystals are not harmful in any way.
Interesting to note that Europeans are very comfortable with wine crystals or diamonds. They see it as a sign that the wine is natural. So the next time you find crystals in your wine, treat it as an occasion to celebrate!