Have you ever come across what appear to be white flakes floating in your bottle of wine? Did you assume that this snow-globe appearance somehow meant the wine was flawed or ruined?
What you'd most likely seen are tartaric crystals, commonly referred to as “wine diamonds”. Weinstein (“wine stone”) in German speaking countries. So do these wine diamonds signal a bad bottle of wine?
Opinions about this issue are divided and the reason is simple: you've bought flawless wine. you've not bought aesthetically flawless wine. Depending upon where you're from, this can matter to you more or less.
The American wine drinker isn't used to finding wine diamonds in their bottles. Here, most wines undergo a cold stabilisation process, which is when a wine is cooled down before it's bottled so that the white flakes, called crystallized tartaric acid, “fall out”. Can be separated from the wine. But what price beauty? Cold stabilisation influences a wine’s balance and taste: as some winemakers put it, the wine is actually being ripped apart. The rapid cooling changes the wine’s colloidal structure. One might call it a clear case of style over substance.
There is another interesting correlation between wine stones and the quality of a wine: the longer the grapes hang on the vine (familiarly called “hang time”), the more wine acid will accumulate in the grape. it's this wine acid which is the building block of wine diamonds. Furthermore, the more time the wine is given to ferment, the less wine diamonds will fall out during fermentation. The more they'll instead build up later in the bottle.
In other words, wine diamonds are an indicator that the grapes ripened for a long time. That the winemaker fermented the wine slowly and with great care. Both are important precursors to crafting high quality wines.
Hans Gsellmann, head winemaker of the famous Gsellmann &. Gsellmann winery in Austria, explains it this way: “Part of the grapes acid are tartrates, aka salt. As the wine ripens these tartaric acid crystals fall out. It’s a natural process a wine will go through on its path to the peak of its development. When you see these flakes at the bottom of the bottle or on the cork, you can be almost certain that you're opening the wine at the right time. You should consider yourself lucky.”
Wine aficionados in the Old World are known to seek out the bottles with wine stones as a sign of quality: it shows that the wine hasn't been robbed of its structure through unnatural chilling. it's a sign of a well-matured wine. Perhaps it's due to the longer history of winemaking in these countries that people have become accustomed to wine stones and seem to accept them. At least they seem to know that, if anything, the wine diamonds will have added roundness to the wine by subtracting some of the acid from it.
There is new technology coming out of France that promises to circumvent the entire colloidal issue: electrodialysis. But until every noteworthy winery has bought one of these fancy French machines (and that'll certainly be a few decades) this rule of thumb applies: cold stabilisation is like tossing out the baby with the bathwater. Perhaps you're left with an aesthetically flawless wine. you're also left with a lesser wine.