There's one more thing that you may not know about your Guinness (which turns out, is a pretty fascinating beer) — it's not exactly vegetarian. That may be a big deterrent for vegans and vegetarians this St. Patrick's Day, the day when it's expected that more than 13 million pints will be consumed by revelers across the globe.
The Smithsonian points out that the popular beer is brewed with isinglass, which many people don't realize is actually fish bladders. Much like gelatin, isinglass is added to cask beers to remove impurities and remaining yeast particles from the final product; the isinglass clumps itself to the particles (which can cause a bit of haziness that freaks drinkers out) and settles to the bottom of the beer. The Smithsonian points out that beers made without isinglass will eventually clear on its own, isinglass finings speeds the process up.
Of course, it's understandable why vegetarians and vegans should pause before ordering a Guinness; The Huffington Post notes that many people may not know that isinglass is used in Guinness, as it's not listed on the website or bottle as an ingredient. But Guinness noted that the amount of isinglass that remains in the final product is "minute," according to a recent statement. But the good news for vegetarian and vegan drinkers is that isinglass is rarely used in beer anymore. The beers to look out for are the cask ales, notes the Smithsonian; but there are plenty of noted vegetarian and vegan beers on the market. And the popularity of vegan beers is rising — if you have a whole beer festival dedicated to vegan beers, it's safe to say it's pretty much a thing.