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Dear Dr. Vinny,
I found what appear to be chunks of glass in a bottle of wine. There was no apparent breakage of the bottle itself, and my friend and I carefully inspected it once the glass pieces poured out. Could it have occurred during bottling?
I haven’t inspected the chunks personally, but my guess is that it was something much less scary—tartrate crystals, which are harmless and a natural occurrence with wine. Sometimes they look like rock candy, sometimes they cling to a cork, and sometimes they look like shards of glass. Odorless and tasteless, they’re just crunchy crystals. I’ve heard them referred to as "wine diamonds," which is sweet and romantic. Who doesn’t want diamonds made of wine?
Tartaric acid is one of the acids found in wine grapes, and it tends to settle out of wine during fermentation and aging. It’s also sensitive to cold temperatures, and when a wine is chilled down, the tartaric acid can drop out of the wine and not dissolve again. Some wines actually go through a cold stabilization process to separate the tartrate crystals before the wines are bottled, purely for cosmetic reasons (and to make sure your wine isn’t crunchy).
If it helps, these crystals are also made from the same stuff that cream of tartar is (most cream of tartar is actually harvested from wine barrels). It’s what keeps my snickerdoodle cookies nice and airy.
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