Sunday, March 30, 2008

Waiter, There's Something in My Wine!

A customer brought a glass of Chardonnay up to me yesterday saying that there was something in it. Before I even looked, I was pretty certain what the culprit was. On looking at the glass, I could see that the customer was concerned about the clear crystals in the bottom of the glass. And I totally understand his concern for I had the same reaction the first time that I ever encountered them. Fortunately, I was with a very knowledgeable wine drinker who explained what they were to me.

He explained to me that the crystals are harmless tartrates, a natural byproduct of the wine making process. He went on to explain that the principle acid in grapes is called tartaric acid and during fermentation and aging, it forms potassium bitartrate (also known as cream of tartar), the potassium salt of tartaric acid. Tartrates are not fully soluble in a weak alcohol solution such as wine, so they tend to want to crystallize and sediment out, the same way that a supersaturated sugar and water solution forms rock candy.

The salt crystallizes and sediments out most readily when a wine is cold, which is the reason that you seldom encounter tartrates in red wine. Older wines also tend to throw tartrates, so their presence can be an indicator of age.

Wine makers take advantage of cold to force tartrate sedimentation. In a process called cold stabilization, they refrigerate the wine to a very low temperature (just below the freezing point of water) to force the crystallization. Then they rack the clear wine off the solids. Other wine makers deal with tartrates by filtering the wine.

Many people believe that both of these processes, filtration most especially, damage a wine, so more and more makers of fine wines are leaving their wines be. If you see tartrates in your glass, it is a good indicator that the wine has not been badly handled.

We do get a few glasses a year returned to us because they contain tartrates. Although we should not serve a glass with tartrates in it, in the low light conditions of the dining room, it can be difficult to see them. Should you encounter tartrates in your glass, you can either ignore them and leave them in the bottom of the glass or you can ask your server to decant your wine to a clean glass. But remember that tartrates are not a wine flaw and not a reason for you to refuse a wine.

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