Why do some wines have sediment and is wine sediment dangerous? Are there different kinds of sediment in wine? Put simply sediment can form naturally in wine both during the fermentation process and while maturing in a bottle. Some wines are more likely to develop sediment and some wines will almost never form sediment. Wine sediment isn't harmful and can be perceived as a sign of wine's quality, but you will normally want to separate sediment from wine before serving and drinking.
Sediment During Wine Production
The initial sediment which forms in wine appears during the fermentation process and is called "lees." The lees sediment consists of dead yeast cells, proteins, stems, bits of skin, and other solid matter that has settled to the bottom of the fermentation tanks. Wine is left with the lees for a while so it can develop more character and complexity, but if the mixture is handled incorrectly some bad flavors can develop.
The initial lees sediment is separated from the wine during a process called "clarification," when the wine is filtered during the transfer from fermentation tanks to aging casks or tanks. In the aging casks more lees sediment can form, so it's not only common for wine to be siphoned out of this first aging cask and into a second to separate it from the second lees sediment, but this process might occur two or three times depending on the wine.
Siphoning and clarification can occur quickly or very slowly depending on what the wine maker is trying to achieve. The more a wine is left in contact with the lees sediment at each stage, the more character and complexity it will acquire. Today you won't find lees sediments in any bottles of wine except among sparkling wines and champagnes made according to traditional methods where secondary fermentation occurs in the bottle itself.
Sediment in Your Wine Bottle
When people think about sediment in wine, they probably think about the formation of sediment in wine bottles that you have to take care to remove before serving. Most people probably don't ever have to deal with that, however, because this kind of sediment only forms in red wines that have been aging for at least eight years, but probably ten years or more. A bottle of wine that you bought a couple of months ago, even if it's a red wine, won't have this kind of sediment.
The sediment which develops in red wine bottles and which you need to carefully remove is formed from tannins and other solid matter that gradually falls to the bottom (or side, if you are storing the wine properly). The presence of this material helps give the wine character and complexity, but you don't want to leave it in the wine when you serve it. First, this kind of sediment can give a nasty, bitter flavor to the wine. Even if the sediment is very mild, it will at the very least interfere with any of the subtle nuances that have developed during the aging process. Second, it's simply not pleasant to look down at red or dark bits in your wine glass.
If you're serving a red wine that's been aging for several years, you'll want to hold it up to the light to see if a sediment has formed. If so, set the wine bottle upright for a few days before serving so all the sediment collects in small area at the bottom of the bottle. When you open the bottle, you'll want to decant it first before serving and possibly aerate the wine as well.
Crystalline Sediment in Your Wine Glass
The tiny crystals you find in your wine glass, and sometimes first in the wine bottle, aren't the types of sediment described above. Fortunately, these crystalline sediments are not only the least likely to taste bad, but are treated by some as a sign of a better wine. So if you find crystal sediment in your wine glass, there's no reason to worry or fret.
The crystal sediment you might find in a wine glass is called tartrate and forms from tartaric acid in grapes. Not all fruit has tartaric acid and its presence in grapes is what allows us to make better wines from grapes than can we can from any other fruit. Because tartaric acid doesn't remain dissolved in alcohol as easily as it does in grape juice, it binds to potassium after fermentation and forms potassium acid tartrates — the crystalline solids creating the sediment in your wine glass. Because red wines have probably been exposed to cold temperatures less than white wines, they are more likely form tartrate crystals.
In theory all wines should probably form tartrate sediment, but modern wine production has introduced cold stabilization and fine filtration which remove most to all tartrates. More expensive wines that have been created according to more traditional methods, thus eschewing cold stabilization and filtration, are more likely to produce tartrate sediment. People who prefer the traditional methods of wine production, which includes a lot of wine drinkers in France and Italy, will treat the presence of tartrate sediment as a sign of quality.
The tartrate sediment in your wine glass or wine bottle won't hurt you if you consume it and it isn't going to ruin the flavor of your wine, so you don't need to worry about separating the crystals from your wine before serving and drinking. However, there is also no value in consuming this sediment so don't go out of your way to do so.