Q: What are these crystals in the bottom of my glass?
A: Here is a question we get from time-to-time in the tasting room by fans of our white wines at Burnt Bridge Cellars. They'll notice a few crystals in the glass or in the bottom of the bottle and wonder what they are?
The answer is tartrates, also known as "wine diamonds," also known as potassium bitartrate, also known as cream of tartar. They are formed naturally as potassium and tartaric acid in wine bond to form a crystal. And they are completely harmless. They form in both white and red wines, although they are more noticeable in whites because white wines typically contain more acid than reds, are clearer, and are cooled when served, which helps these crystals form.
At Burnt Bridge Cellars, we see them most often in our Semillon, which typically comes in with higher acid than our Viognier or Marsanne. This year's Carte Blanche, for instance, is a blend of all three, and the crystals are evident at the bottom of most bottles. They don't affect the taste of the wine at all and are safe to consume.
At larger, mass production wineries, winemakers are trying to make the most uniform product from year to year. When wine is made in large tank farms that are the size of football stadiums, consistency is the key to profits. At some point customers bought this wine, noticed some tartrate crystals in the bottle and thought they were glass shards or a flaw in the wine and complained. So, instead of educating their customers, these large companies decided to get rid of these natural forming and safe little crystals by a process called cold stabilization.
Basically, they take the wine, rack it to a big tank, and chill it down to 30 degrees or so for a couple weeks using a glycol chiller. The tartrates form in this cold environment, fall to the bottom of the tank and the wine is then transferred off of the tartrates. This is a fairly expensive and energy intensive process and doesn't improve the taste or quality of the wine. In fact some believe that stripping these tartrates out negatively affects the wine's flavor and mouthfeel.
We don't have a glycol chiller at Burnt Bridge Cellars, and don't have plans on getting one anytime soon. If you need your wine to be uniform and crystal free, there are thousands of examples available at most convenient stores. We like our wines as they are, however, wine diamonds and all. And we hope you do too.