Wine diamonds

Another good question: "We were lucky enough to be given a bottle of the Shiraz from a friend to try, and although we loved the taste, there was extremely heavy sediment in the bottom of the bottle that actually clinked the glass when dropped back in. We are concerned about the toughness and hardness of this sediment, can you advise us as to what it could be and if this is common, before we consider buying some wine ourselves. And this did detract from our full enjoyment of an otherwise tasteful wine. Thank you for your time with this matter"
Answer: "Tartrate crystals, also known as wine diamonds, potassium bitartrate crystals, or cream of tartar, occur naturally in wines that are high in tartaric acid, which is the sign of a quality grape. Tartaric acid is the primary acid found in grapes, just as citric acid is found in oranges, lemons and other citrus. In wine, the tartaric acid binds with natural potassium, forming potassium bitartrate. The crystals precipitate either to the bottom of the fermentation vat, adhere to the inside staves of the oak barrel, or form in the bottle, especially if the wine is chilled. In the bottle, the crystals are usually found just under the cork or at the bottom of the bottle, depending how it has been stored or transported. Tartrate crystals do not in any way alter the taste of the wine, but they are displeasing to the eye. If tasted, they are slightly tart but not unpleasant, just like the cream of tartar you might add to beaten egg whites to form a meringue. To avoid this, gently decant the wine to separate the wine from the crystals. You will also find a general improvement in the taste of red wine when it is decanted.
Because most Australian drinkers are not familiar with wine diamonds as they are in Europe, some Aussie wines are "cold stabilised" at the winery to remove the crystals before bottling. Chilling the wine to near freezing for a period of days accelerates the formation of the crystals, which are filtered out. Apparently the drawback to this technique is that there is the potential for oxidation of the wine since chilling makes oxygen more soluble. Our philosophy is to use the most gentle winemaking techniques possible, with minimal intervention, to maximise the wine's individuality and structure. Therefore our reds are not cold stabilised, and we sometimes find a few harmless wine diamonds in the bottle.
I hope this is a helpful answer to your question. Its a shame I didn't explain this to you earlier, as you may have enjoyed that wine more!"