[General Reading] --- Something fishy lurks in those lees, finds Christopher Middleton

Published: 12:01AM BST 02 Sep 2006


It's an amazing thing, a fish's swim bladder. It works like a submarine air tank, enabling its owner to rise or dive at will. The other amazing thing about swim bladders is that you frequently find them in beer and wine. Not propped up in the glass, or floating on the surface, but in dried and powdered form, lying on the bottom of the bottle or barrel like sand on the seabed.

Yes, the strange and slightly unnerving fact is that few things filter out the unwanted particles in bitter or Bordeaux better than a handful of desiccated and ground-up fish intestine, known as isinglass. It used to be only the sturgeon whose bladder did the business but, since that particular species became scarcer, other finned creatures such as catfish and threadfins now lend their innards to the cause.
"The bladder shapes vary from one type of fish to the other," says Christine Fleming of Murphy and Son, the Nottingham-based suppliers of filtering agents to the brewing industry since 1887. "Some bladders are round and heart-shaped, some are long and leaf-shaped, and others are pointed, like spears. What they've all got in common, though, is collagen, which is extremely good at collecting yeast particles." There are roughly five million in every teaspoon of real ale. That is, before the collagen gets going.
"What's at work here is an electrical process," says Ken Don, head brewer for Young's in London. "The ions in the collagen have the opposite charge to the ions in the yeast, and so attract them like a magnet. They all join together in a mass and sink to the bottom of the cask. It's quite a quick process; all over within 24 hours."
And despite the fact that the mashed-up bladder has a fishy, eggy odour when it is plopped into the beer (in paste form, after water has been added), it doesn't leave any dubious aftertaste. This is why "fining", as it is known, has been in use for centuries, rather than being dismissed circa 2,000 BC as an experiment that went wrong. ("All right, who put fish paste in my pint?")
"No one knows for certain how the practice began," says Iain Loe, of the Campaign For Real Ale (Camra). "My theory is that the Ancient Greeks found that wines stored in bladders were less cloudy than those stored in pottery amphorae. And when people started drinking out of glasses, they would have demanded less cloudy liquid." Without being too choosy about how that effect was achieved, it would seem.
Even today, wine producers aren't rushing to let you know that their grands crus contain fish bladders. One of the few firms to volunteer the information is the Co-op. "We list all the ingredients used in our wines and beers on the label," says the Co-op's wine marketing manager, Vicky Steel. "Even though it is not contained in the end product, we believe that vegetarians have a right to know that isinglass has been used."
Not that you could tell the difference with your tastebuds. Provided the producers have been doing their job, the fish-omelette "floc" (ie dregs) will stay firmly at the foot of the barrel and never pass the punters' lips. With wine, it'll never make it into the bottle in the first place; with beer, it'll be returned to the brewery with the cask (landlords always leave at least one per cent of a barrel's contents untouched at the bottom).


Which means none but the most strict vegetarians need fret about sturgeon in their stout or catfish in their Côtes du Rhône. And, on the environmental side, it's hard to come up with any more constructive use for a redundant fish bladder than making wine and beer more enjoyable. But if you think of one, do write in and let us know.

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