Most of our beers are brewed using nothing except malt, hops, yeast, water, and (sometimes) sugar. There's some unmalted barley in the stout, and we've been known to
We do have some flaked maize in the malt store, but we haven't used it in anything yet. If we do, we'll tell you.
Since all our cask output is "real ale" it will contain live yeast, which can cause a visible haze in beer and may contribute interesting tastes and aromas in the finished product.
Animal products in beer.
Many pale beers will have been processed using fish derived "isinglass" finings, to produce a "clear" product by promoting a rapid and stable settlement of yeast. Brewers typically add isinglass as the beer is transferred to cask, and while pretty much all of this will remain in the cask as sediment, it does mean that beers fined this way cannot be enjoyed by vegetarians / vegans. Some brewers even use isinglass in their dark beers.
It's not just beer - wine producers might use any, or all, of: isinglass, gelatin, egg albumen, modified casein (from milk), chitin (derived from the shells of crabs or lobsters) or animal blood.
Some brewers manage to avoid the use of isinglass by relying on a highly flocculent yeast or by sending beer out with rather low levels of residual yeast. We've found that neither of these approaches will give us beer that reliably conditions in cask and suits normal cellar operations. Personally, I don't mind hazy beer as long as it's clean, and I find that small amounts of suspended yeast help, rather than spoil, the taste of beer. However, we've found it pretty near impossible to sell unfined pale beers, so we do normally use isinglass in them.
Not needed in dark beer.
On the other hand, our dark beers work perfectly well without finings, so we don't put any in, making them suitable for everyone, including vegetarians and vegans. Yay!
Any utensils or containers that may have been in contact with isinglass will, as a matter of course, be cleaned thoroughly after such use, and before being used for anything else.
Bottled and kegged beer.
Given that beer destined for bottles and kegs will usually be filtered (or centrifuged) to remove yeast and other hazes, you might think that these products won't have been processed with isinglass or animal gelatin. This is often not the case. Depending on the kind of filtration used, the filter run or use of consumables can be improved by fining beforehand.
We're just looking at bottling now. We hope that we'll be able to avoid finings, but this is liable to have a slight cost impact on the finished item.
Even bottle-conditioned beers may have been fined, but you should check with the brewer.