Answer: not as often as you’d think …
Beer is ages old. You’ve all heard the stories. It goes back hundreds if not thousands of years. And traditionally, it involves four ingredients: water, malts (barley or other gains), hops and yeast. So far, everything checks out vegan here … Now, some craft or micro brewers have been adding specialty ingredients to give their beer the edge. From honey to milk chocolate (note: not all “chocolate” beers have milk. In fact, hardly any of them do. The “chocolate” in question actually refers to the type of malt used), anything goes these days. Again, mostly vegan.
The ingredients check out safe, for the most part. However, the clarifying or fining of the beer is when things start to get dicey. Clarifying is the process of making the beer look nice and shiny. It removes solids and proteins, for the most part. Beer makers use different products to clarify beer. Everything from gelatin (not vegan) to isinglass (fish bladders. No joke. Fish bladders). These products may show up in the finished product in VERY minute quantities. Beers that use isinglass range from Guinness to Newcastle to plenty of other UK based beers.
Fun fact for craft fans: one of the brewers at Flying Dog Brewery was/is vegan (I can’t verify if the individual still works there)! And yes, their beers are vegan friendly (minus one made with honey).