Many wine drinkers think there is a problem when they see tartrate crystals in the bottom of their wine glass. But there is absolutely nothing to worry about, other than visually. Potassium tartrate crystals or ‘wine diamonds’ as they are sometimes called, form naturally during the course of the winemaking process and are small, transparent or white.

There are many natural grape acids, the main one being tartaric, others include malic, lactic, acetic and citric acid. If the grapes are harvested early with a fairly high acid content, there will be a greater chance of tartrates settling later on. It occurs predominantly with white wines grown in cooler climates or at higher altitudes that would be less ripe than those grown in warmer locations.

As grapes ripen, their natural sugar content increases while at the same time their acids decrease, so it is very important to pick them at the optimum level of both sugar and acid content. Sometimes this is not so easy to do due to bad weather that slows down ripening and keeps acid levels high. Typically from these grapes, when made into wine, tartrate crystals are likely to form.

After fermentation is complete and the wines have been racked, there is little or no natural sugar in the wine. It is at this stage that the wine tastes its worst, which is very astringent with acids in the foreground and no balancing sweetness. What is needed now is to try to reduce the acid level without additives, so when cooling the wine, usually by cold stabilization, tartrate crystals will form and settle to the bottom of the container. The wine is then racked again before the wine is warmed.

Although most of the tartrate crystals will be removed, some will not have been removed. They will have dissolved back into the wine and are therefore ready to settle in your glass after you’ve had your bottle in the fridge or cold cellar, before opening.

Why are ‘Wine Diamonds’ or tartrate crystals a sign of quality?

Acids are very good friends of winemakers, as long as they are not excessive, as a wine with a lot of acidity will keep much better and longer than one with a lower acidity level which will tend to be lackluster and mushy.

With more and more great white wines being produced at high altitudes, it is these acids that are giving them a seal of quality. Of course, the wine must have good natural sugars to create that vital sugar/acid balance that all winemakers strive to achieve with their wines. But without enough tartaric acid, the wine would have no structure and no backbone.

The crystals themselves are completely harmless, it’s just a matter of aesthetics, so the next time you find yourself with what looks like sugar granules at the bottom of your wine glass, don’t worry, just think “quality”. .