Just about every wine retailer in the United States has, at one time or another, faced this problem:
A patron comes into the store with a bottle that he or she has purchased there and wants a refund, arguing that there is “broken glass” in the bottle. Most likely this is a white wine or a rosé and the patron is angry. And the retailer faces having to return the wine to the winery or wholesaler for credit.
Partially as a service for these people, I periodically set the record straight and write about this issue, which came up again last week with a superb rosé wine I tasted. (See Wine of the Week below.)
Interestingly, this wine happens to be as good as it is precisely because of the shards of “glass” that developed in the sealed bottle.
The explanation is slightly complicated: After a wine’s fermentation is over and the wine is almost ready to be bottled, the liquid retains elements that could cause harmless sediment to form in the bottle under some conditions.
Many such wines have tartaric acid, which is dissolved in the wine and is invisible. However, if any wines containing tartaric acid are chilled for several hours, the tartaric can fall out of solution and form crystals.
When this occurs, winemakers say the wine has “thrown a sediment.”
So although white and rosé wines are best served cold, very cold chilling of these wines, especially over several days, can cause sediment to develop. It looks like broken glass and prompts some buyers to think the wine has gone bad.
To prevent this from occurring in wine buyers’ home fridges or in restaurants with very cold walk-in refrigerators, most wineries do something they mostly would like to avoid doing. They cold-stabilize the wines at the winery to drop the tartaric acid out of the wine before it is bottled.
The reason most winemakers dislike this tactic is that it is not being done to improve either the aroma or the taste of the wine. It is done purely for cosmetic reasons.
Some people, especially wine marketing people, think the sediment looks bad and may be taken by some buyers as a flaw. In fact, I could argue that the appearance of tartrate crystals in a bottle is a sign that the winemaker was so certain that cold stabilization would harm the wine, he or she avoided doing so or minimized how it was done.
Cold-stabilization entails putting the wine into a tank and dropping the temperature inside the tank down so the sediment forms there and can be removed from the wine before it’s bottled.
Many winemakers believe strongly that the colder the wine gets during the stabilization phase, the more the wine is negatively impacted.
Cautious winemakers drop the temperature down to 40 or 45 degrees Fahrenheit and hope that’s sufficient. A more conservative approach is to stabilize at a lower temperature, to make sure no crystals will develop after bottling. But the negative impact can be worse.
With wines that aren’t cold-stabilized low enough, once the bottle goes below the temperature at which it was stabilized, some of the remaining tartrate crystals that are in solution may yet separate from the wine.