De Beers opened its first Hong Kong outlet, at The Landmark, last week. The company would have you believe diamonds are a girl's best friend - and many wine connoisseurs would agree. Wine diamonds are increasingly rare these days. Wine diamonds, or weinstein (wine stones in German), are the small, mostly clear crystals sometimes found clustered on corks or sparkling in the base of your wine. These glittering diamonds are actually tartrates, derived from tartaric acid, a natural ingredient in grapes and many other fruits, including bananas and tamarind. The tartaric acid precipitates or 'falls out' in a crystallised state when wine is chilled to a very low temperature. In northern European wine regions, these crystals form naturally while the wine matures during the long chilly winters. Later, during the warmer spring and summer months, the wine is lightly filtered to prevent loose crystals from entering the bottles and cellar hands begin scraping away tartrate crystals clinging to the insides of barrels and tanks. The scrapings are subsequently converted to cream of tartar, a baking aid used to stabilise egg whites in meringues, souffles and angel food cakes. Tartrates can appear as pretty diamond-like crystals or flat whitish flakes resembling the snowflakes floating in Christmas snow globes. Clear crystals are tartaric acid bound with potassium, whereas white flakes are bound with calcium. Because this crystallisation does not occur naturally in warmer wine regions, the precipitation may inadvertently take place after bottling, say in the chilly cargo hold of an aeroplane - or on an overly cool refrigeration rack. Interestingly, opinions are divided as to whether the presence of wine diamonds is advantageous or unfavourable. Though harmless, consumers unused to tartaric acid sediment can find it unattractive, with some fearing the crystals are hazardous glass shards. As such, many winemakers artificially induce the crystals to form before bottling through a technique called cold stabilisation, in which the wine is chilled rapidly for a brief period. Some winemakers are adamantly against cold stabilisation, arguing it alters the wine's structure and causes unfavourable changes in character. Certainly the precipitation of tartaric acid means the wine's final acid levels will be lower than originally intended by nature. Other techniques include chemical additions to 'seed' the crystals or the use of less romantic, but less invasive, electrodialysis machines. An interesting link between wine diamonds and quality has to do with ripeness levels. In a cool climate, the closer a grape gets to peak ripeness, the higher the tartaric acid levels. Thus, in chilly Germany, where the grapes have difficulty reaching maturity, wine diamonds can indicate that the grapes were fully ripe at harvest. Some traditional European connoisseurs actually seek out bottles with diamonds as they are perceived to be carefully made, well-matured wines. On the flip side, warmer regions struggle to keep acid levels sufficiently high, so many winemakers avoid cold stabilisation because it reduces precious acidity. They prefer to bank on their consumers to understand if diamonds appear. Not sure that you'll find time to visit De Beers? Toss a few German rieslings into the back of your refrigerator. Those who covet pink diamonds could try stocking their fridge with rose. Ruby lovers can opt for red wines long-matured in cool cellars. Whatever your preference, be aware that tartrates are water soluble and most will dissolve in your mouth - proving what we suspected all along. Diamonds aren't forever.