Are there diamonds in your wine?

Tartrate crystals stuck to the bottom of a cork

Ever noticed clear crystals floating in your wine or perhaps stuck to the bottom of the cork? From their appearance, folk often believe they are sugar or salt or sediment or …….. shards of glass!! Unless of course the glass or bottle has been broken, they’re none of these.

Sediment in a glass of red wine


Sediment is made up of yeast cells and winemaking left overs e.g. stems, seeds, grape skins etc. that can occur naturally during fermentation and maturation. Whilst the sediment may include an element of crystals, crystals are different.  Wines that throw a sediment are typically red and/or aged and/or unfined and/or unfiltered wines.

Many consumers prefer their wines not to look cloudy or hazy. At the clarification stage, a winemaker can use a fining agent, which in simple terms is a substance that attracts another substance to coagulate with it so that they can all be extracted together.  Added to wine, a fining agent helps to improve clarity. Fining agents include isinglass (gelatin from fish e.g. sturgeon), casein (protein found in all mammals milk e.g. cows, goats etc),  egg white, and for vegans bentonite.  Previously bulls blood was also used until it was banned in the EU following the BSE crisis. Whilst some fining agents don’t sound that appetising, post fining no detectable amount should be left.

Fining and filtering (latter is the removal of insoluble elements) are the two methods to remove the sediment before the bottling stage. This way a wine looks bright and clear, the way the vast majority of people prefer their wine to look.  Some winemakers prefer not to do one or both as they believe that some of the characteristics of the wine will be stripped away in the process. Wine labels usually note if the wine has been unfined and/or unfiltered and/or suitable for vegans for consumer emphasis and awareness.

Tartaric Acid

Malic acid, citric acid & tartaric acid are naturally found in grapes

Malic acid, citric acid and tartaric acid are naturally found in grapes. Tartaric acid is found in other fruits like bananas, citrus etc. and contributes to the tartness in wine as well as helping protect it from spoiling. If, however, the grapes have been harvested too ripe (typically in hotter climates), they will have a higher sugar content, lower acidity and higher pH (the latter can cause wine instability, off flavours and an increased potential to deteriorate faster). Legislation permitting, tartaric acid (and malic acid) can be added to increase the final acidity level of a wine and improve the stability – this is called acidification and whilst it can be done pre or post fermentation, pre enables better integration.

White/green grapes contain more tartaric acid than red/black grapes. Unlike malic acid, tartaric acid maintains its chemical makeup during winemaking and is the most prominent acid in wine with the bulk of the concentration present as potassium bitartrate (also known as cream of tarter in cooking).

Newly made wines are typically saturated in potassium bitartrate, which is susceptible to temperature fluctuations. So, if a wine is exposed to cold temperatures, its solubility limit is exceeded and the excess triggers the production of tartrate crystals or, as they are more fondly known, wine diamonds. The cooler the temperature the wine is subjected to a greater number of wine diamonds will form.

The cooler the temperature the wine is subjected to a greater number of wine diamonds will form

Wine is often shipped around the world inside containers in the hull of ships that sail through very chilly seas and oceans. To stop wine diamonds occurring during shipment or even in your fridge at home, lots of white wines are put through a process called cold stabilisation. The purpose of cold stabilisation is to create and then remove the excess potassium bitartrate before bottling. Some winemakers won’t carry out this process as they regard the existence of wine diamonds as a mark of quality and verification that their wines have had less manipulation during its production in the winery. Non-cold stabilised wines are therefore more likely to create these tartrate crystals when chilled.

Once wine diamonds/tartrate crystals and/or sediment has formed, they’ll never dissolve or disappear. Yet it is important to understand that they are completely harmless and don’t affect the quality, aroma or taste of your wine. If you find the grittiness and/or texture rather unpleasant in your glass, just decant the wine or filter it through a muslin cloth before pouring.


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