As the pictures above show, tartrates are small crystal-like substances and are often mistakenly assumed by consumers as a fault with the wine, thought to be sediment, sugar or even shards of glass. Ask any Sommelier in a restaurant; they should be able to give you at least a few accounts of glasses / bottles of wine being sent back due to tartrates being found.
So what are tartrates?
Tartrates form in wine when naturally occurring potassium and tartrate molecules bind together in cold temperatures. Tartrates are essentially cream of tartar, and once a winery removes them (if they so choose), they can go on to sell them to the baking industry.
In order for a winery to lessen the likelihood of tartrates in your wine, they can attempt to remove them at the source by "cold stabilizing" stainless steel vats, bringing the temperature of the wine down to near freezing. The process isn’t cheap, and the equipment also costs a fair amount of money. This process makes the crystals cling to the sides of the vat, and the wine is then filtered off. The method isn’t always 100% effective, but if not carried out tartrates may form later in the bottle, especially if stored at a low temperature. For this reason, you normally see tartrates in white wine more than red wine, although older reds are also sometimes susceptible.
Winemakers are divided over whether processes such as "cold stabilization" in order to remove these "Wine Diamonds" (a cute term for tartrates) harm a wine by stripping it of flavor. In Europe, tartrates in a bottle of wine are common-place and even encouraged, due to their presence being an indicator of a more naturally made, sometimes higher quality wine. However, consumers in the U.S. are used to seeing clear, pure, filtered white wines with no particles, and so the presence of crystals can sometimes create panic!
Once you realize that your wine has a bad case of the tartrates, the only way to separate them from your wine is to decant, or pour it slowly into your glass. The one saving grace is that you can be safe in the knowledge that you are drinking a wine that has been handled with the utmost care.