http://www.bbc.com/news/uk-england-37350233
Ask somebody to list the classic ingredients of beer and the chances are they will come back with: hops, malt, barley and water, with a bit of yeast thrown in for good measure.
It is unlikely the swim bladder of fish would be on the list, but isinglass - a gelatine made using the organ - is in fact very likely to be in your average pint.
Used since the 19th Century as a fining agent to make beer clear, bright and more attractive to drinkers, the odourless added extra is used widely by brewers, from mass-produced brands to small microbreweries.
Its prevalence poses a problem for vegetarians and vegans, many of whom do not realise they need to tread carefully when ordering at the bar.