Understanding Wine Diamonds
Grapes naturally contain several organic acids including tartaric acid (wine acid in German). They also contain potassium and calcium ions, which form salts with the organic acids. These salts can precipitate out of the wine to form a material called potassium (calcium) bitartrate. This is a clear (sometimes red or brown), crystalline material also referred to as "wine diamonds," but vintners will also refer to them as "tartrates."

These bitartrate salts have several interesting physical properties.

  • In the unfermented grape juice only a little of the bitartrate can be dissolved.
  • Even less of the bitartrate is soluble in the juice (now wine) after fermentation, since alcohol dissolves less of it.
  • The quantity of potassium bitartrate dissolved in wine is strongly related to temperature. Cold wine cannot hold on to as much bitartrate therefore they will drop out of the wine whereas warm wine will drop out albeit at a much slower pace.

In combination, these three properties produce an interesting winemaking challenge. As the alcohol concentration increases during fermentation, the new wine becomes saturated, and tartrate precipitates out of the wine. By the end of fermentation, the new wine is over-saturated with tartrates. The tartrate continues to drop out of the solution, but at normal cellar temperatures the tartrate precipitation is very slow. Often the tartrate crystals continue to precipitate for a year or more.

As the tartrate continues to drops out of solution, suspicious looking crystals are formed in the bottle, or dense sediments form. Tartrate sediments are unsightly, and are sometimes mistaken for glass particles. However, they are in no way harmful nor do they spoil the wine.

When a wine kit contains more juice, chances of acid instability is higher. With this the wine industry regards a tartrate dropout more of a sign of quality than a problem or an issue. Commercial wineries cold stabilize their wines to avoid tartrate dropouts. Cold stabilizing is the process of dropping the temperature of the wine, after fermentation, to close to freezing for 1-2 weeks. This will cause the crystals to separate from the wine and stick to the sides of the holding vessel. When the wine is drained from the vessels, the tartrates are left behind. All of our premium wines are treated with a metatartaric acid to help reduce the tartrates. This does not effect, clarity, nose, or taste –so no need to worry.

At the Wine Bottega we always strive to produce the highest quality wine, the most natural way. For this reason you may continue to experience tartrate dropouts in some of our premium products. We are sure that you understand this dilemma that nature provides, not only to us but to the whole wine industry.