Sedimentary, my dear Watson!
We’ve all had it happen before. Get to the bottom of a perfectly good bottle of Malbec, especially one that’s got a few years on it, and all of a sudden your stemware gets coated with something that looks like a grizzled 18th century prospector just used your fancy Austrian sippy cup as a tobacco spittoon.
The first thing you need to realize is that wine does not come from a faucet, it does not come from some font in the middle of a well-maintained topiary garden, it comes from grapes. Grapes that are squished, fermented, strained, aged and then slapped in a bottle. Given this process, do you think it’s unreasonable that there might be some plant-nasty in that bottle? I certainly don’t think so.
So what is this stuff, anyway? In red wine, sediment tends to be a byproduct of the chemical breakdown responsible for mellowing a wine as it ages. All manner of long polyphenol chains like tannins break down and soften over the years. As this happens, bits of these chains can coalesce and settle on the bottom of the bottle or on the underside of the cork (since you’ve been storing your wine properly on its side riiight?).
In whites, along with some reds, the other kind of sediment you’re likely to see is stuff that looks like salt crystals. These are called tartrates, and are what happens when the wine is cooled and the tartaric acid combines with naturally occurring potassium and forms potassium bitartrate salts. These precipitate out and blah blah blah you know the drill at this point. They’re harmless, ubiquitous, and in some places like Alsace, years of use can coat the insides of fermentation casks with the stuff.
“But Steve,” you inevitably interrupt, “doesn’t a lot of wine undergo modern processes like filtration and fining?”
You are correct, dear reader, and for that I am proud of you. Here, have some reward salt.
Modern winemaking certainly can embrace techniques like filtration (in which the wine is forced through a number of physical filters that separate out excess plant solids, yeast, unfermented sugars, etc), and fining (in which a “fining agent” such as egg yolk or bentonite is introduced to a tank of fermented wine in order to coagulate impurities and help them precipitate out of the liquid), and in wines that have undergone these processes you are less likely to encounter sediment. That said, processes like these can strip the wine of nuance and character, so a lot of high end wineries (like the type Lot18 tends to hang around with) tend to eschew them.
What can we take away from this? Embrace the gunk! It’s a sign that your wine has been loved for who it is, not what someone thought it should be. Its parents let it go to that liberal arts school instead of forcing it to become a dentist like its father. And we all know that no tasting note is quite as unpleasant as regret.