Often referred to as “wine diamonds,” these solids are actually tartrates that form in wines that typically have not been treated.
Tartrate crystals, considered by the average consumer to be a fault in wine, can be mistaken as sugary particles or even broken glass. Many wine books shed light on the topic. However, I think David Bird says it best in his book Understanding Wine Technology: The Science of Wine Explained. Written for the non-scientist, Bird explains what tartrate crystals are and how they occur.
“This deposit is not tartaric acid, as is commonly thought, but is either calcium tartrate or, more likely, potassium bitartrate (cream of tartar), originating in the grape. This is caused either by a poorly conducted stabilisation process or by the initial presence of protective colloids, which have prevented the deposition of the crystals during the stabilisation process and which have subsequently denatured.”
He goes on to explain what colloids and denaturization are, but I won’t numb you with the details. What’s important is that you gain a basic understanding of this phenomenon so that you can further appreciate wine.
To prevent tartrate crystals from occurring, winemakers can chill the wines to near-freezing—a process called “cold stabilization”—causing the tartrates to precipitate out. The wine is then filtered to eliminate the crystals. This procedure, however, can be costly and may not guarantee results.
Since cream of tartar originates in the grape, it would make sense that tartrate crystals would be a natural element in wine. Nonetheless, most consumers wince at the sight of these deposits. I can’t tell you how many times the phrase “Yuck! What’s that in my glass?” has been uttered across the tasting bar. For me, tartrate crystals register nary a blip on my “yuck” radar. Sulfur dioxide or “smoke taint” is more likely to make my nose curl.
Tartrate crystals won’t kill you or change the flavor of the wine. If anything, they may taste slightly bitter. There are two things you as a consumer can do to eliminate them:
1. For white wine, set the bottle upright for a while to allow the crystals to fall to the bottom. Then slowly pour the wine, keeping an eye on the deposits so that they do not flow toward the neck of the bottle and ultimately into the glass. For red wine, set the bottle upright as well and remove the entire capsule (foil). After a while, tilt the bottle using one hand—with your other hand, shine a flashlight on the underside of the bottle’s neck while pouring to spot any crystals.
2. If you do not have a steady arm and a keen eye to do Step 1, you can filter the wine—either into your glass or into a decanter—using a wine funnel that has a removable screen.
Tartrate crystals can also end up on the underside of the wine cork. If so, brush them off with your finger. Just make sure your hands are clean; you don’t want to contaminate the cork if it’s going back in the bottle.
I recently came across this beauty of a crystal that had been stuck to a cork. It’s nearly the size of a half-carat diamond.
So there you have it. Hopefully, I’ve been able to dispel somewhat the myth of wine diamonds. The next time you experience tartrate crystals, just embrace them. There are more important things in life to worry about.