People online have recently been mortified to learn that some beers contain a product derived from fish bladders.
Some breweries use isinglass, which is a gelatine-like substance from drying and processing certain fish bladders. It is part of the flocculation process to alter the colour of the beer.
Explaining the technicalities, Craft Beer & Brewing said: "Isinglass is a traditional finings, a substance that causes yeast to precipitate out of suspension, leaving beer clear. Isinglass is derived from the swim bladders of certain tropical and subtropical fish.
"When macerated and dissolved for several weeks in dilute food-grade acids, they form a turbid, colourless, viscous solution largely made up of the protein collagen. This material is known to brewers as isinglass finings."
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However, it's worth noting that with advances in filtration technologies, isinglass is not as common anymore.
"The use of isinglass has declined and today it is largely confined to cask-conditioned ales," Beer & Brewing explained. "Although some American craft brewers also use it to clarify beer without the use of filtration."
Guinness famously altered their recipe after 256 years to become vegan-friendly.
In 2016, a spokesperson told The Times: "Whilst isinglass is a very effective means of clarification, and has been used for many years, we expect to stop using it as the new filtration asset is introduced."
Of course, the use of the substance makes some beers not suitable for vegans. But, in the meantime, there are plenty of alternatives that don't contain the fish product including Heineken, Peroni, Birra Moretti and Camden Hells.
If unsure whether a beer is isinglass-free or not, Barnivore is a great place to start with a database of almost 40,000 beers and their ingredients.
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