The fishy reason why wine isn’t suitable for vegans:
On a recent trip to Aquitaine, near where the might Dordogne and Gironde rivers meet as they flow into the Atlantic, a friend showed me a book that he had picked up at a local brocante (antiques market). It was an 18th century English book on angling. The entries concerned the various fish to be caught in the rivers of Northern Europe and, importantly, what to do with them (”… the flesh is firm and satisfying to the palette, but the livers are usually discarded as they are often measly...“); among them, one stood out: the “isinglass” fish. It was a monstrous beast said to grow to 24 feet in length and to weigh more than 400 pounds. This fish, aside from its seemingly implausible physical characteristics, had a particularly special purpose that gave it its curious name. It’s bones were to be boiled and the resulting liquid refined into isinglass, which, the author went on to say, was of special importance to vintners. Surely this was a flight of fancy on the author’s part, a fish that none of us had ever heard of, that was the size of a crocodile and that would be boiled and added to wine?
This was no fairytale monster, however. The fish in question is one that almost everyone has heard of, though for an entirely different reason, and which has all but disappeared from the rivers of the Atlantic coasts of Europe and so is now associated with Russia and the east. It is, in fact, a sturgeon, which really do grow to enormous proportions and which are famed for their roe, called caviar. In 18th century, the market for caviar was not what it is today and so the fish was prized for the proteins that it proceeded in vast quantities, which could be refined into isinglass. The isinglass is still used to this day to clarify wine, that is, to remove tiny solid particles that are still present in the wine as it becomes ready for bottling.
The process is much the same as doing clarification of a stock to make consommé, in that case you use egg whites, but essentially all you need are fine protein strands that can trap the tiny particulate matter. Today, is glass is produced from the swim bladders of a multitude of different fish, and, though some producers have found synthetic or plant based proteins that can do much the same job, the fact remains that this is the reason why wine is not normally vegan.