Unless of course a bunch of junk is added so it can be sold faster
Wine seems like a simple drink. This is why so many people enjoy it, they feel like they're consuming something that is a single ingredient crafted with ancient techniques. This is true sometimes, but many wineries are using creative processes for fining their wines. And when I say creative I don't mean with flair, I mean with cringe-worthy additives.
For those unfamiliar with the term fining, it's the process where a substance (fining agent) is added to the wine to create an adsorbent, enzymatic or ionic bond with the suspended particles, producing larger molecules and larger particles that will precipitate out of the wine more readily and rapidly. Why do they use these methods? First, not every winery does, but those that do are likely bigger companies that have wide distribution and a business model that requires them to be able to deliver product to their supplier in expected quantities, on time and, most importantly, tasting good. Wine making is a tricky process though and coming up with the perfect bottle of wine every time isn't possible, so different ingredients are introduced to manipulate things like pH and chemical balances that affect taste. Another factor is the equipment itself affecting the taste, sometimes through introduction of particles from metal equipment, also more likely found in larger wineries. The end product then has minute amounts of these compounds which is regulated by the government of the country where the wine is made and sometimes importing countries.
The compounds used as fining agents are often animal based, a possible cause of concern to vegans. The most common compounds used include egg whites, casein derived from milk, gelatin and isinglass obtained from the swim bladders of fish. In a process known as blue fining, potassium ferrocyanide is sometimes used to remove any copper and iron particles that have entered the wine from bentonite, metal winery and vineyard equipment, or vineyard sprays such as Bordeaux mixture. Because potassium ferrocyanide may form poisonous hydrogen cyanide its use is highly regulated and, in many wine producing countries, illegal including the USA, but it is still legal in Australia and New Zealand. Fortunately there are more vegan-friendly processes being implemented by some wineries in response to public concern. Pulverized minerals and solid materials can also be used, with bentonite clay being one of the most common for absorbing proteins and some bacteria. Activated carbon from charcoal is used to remove some phenols that contribute to browning as well as some particles that produce "off-odors" in the wine. Even though these are fully removed from the final product, on their own they aren't toxic or unsafe to consume in small amounts on their own.
The US Government Publishing Office has posted a list of materials authorized for the treatment of wine and juice.
 A word you'll see a lot throughout this list is GRAS. This is an acronym for Generally Recognized As Safe and as a policy it's about as vague and effective as it sounds. The FDA grants a GRAS label to products/additives that the manufacturers themselves have deemed to be safe but that the FDA itself has not approved. It's a method of self-regulation that many consider to be dangerous because its safety is left up to those that stand to profit from it. Rather than going through the painstaking FDA-led review process to ensure that a new ingredient is safe, food companies can determine on their own that substances are "generally recognized as safe." The manufacturer can then ask the FDA to review their evaluation at the FDA's discretion, but they aren't required to. If they choose, they can take their ingredients straight to market, without ever informing the FDA.
 The FDA may also decide they don't want to bother reviewing the ingredient.
Here's an informative little video that outlines this process with a stunning example of how it can fail us.
The Government of Canada has a broader list of allowable food processing agents and additives that includes wine. I've heard that Canada has stricter regulations when it comes to food safety but the information is a little harder to find so I'll be working on a follow up article to provide more information about this topic specifically for Canadians. I didn't want to wait to share this with you because I want you to be able to make better choices for your next dinner party.
Here are a few resources to find a vegan wine near you: