The market for vegan and gluten-free beers is still relatively small, but is expected to grow as millenials become increasingly concerned about what they eat and drink.

Last year, Guinness became vegan-friendly as the Diageo brand eliminated isinglass, a product made from fish bladders, from the brewing process.

And according to recent rearch from GlobalData, 8% of the consumers in the UK aged 18-34 associate ‘gluten-free’ with ‘healthy’, compared with 5% of the overall population.

According to CAMRA, the key ingredient that determines whether a beer is vegetarian/vegan or not is finings.

These are used to clarify beer by pulling yeast sediment to the bottom of the cask and are usually made from isinglass, an extract from the swim bladder of the sturgeon fish.

Although the finings drop to the bottom of the cask with the yeast and are not consumed, the use of an animal product to produce the beer is objected to by strict vegetarians and vegans.

Some brewers don’t fine their beer, but this means the beer needs longer to settle before serving in the pub and still turns out hazy or even cloudy in the glass. Others use finings made from seaweed, but this is mostly confined to bottled beer usage.

Gluten-free beer is beer made from ingredients that do not contain gluten such as millet, rice, sorghum, buckwheat or corn (maize). People who have gluten intolerance have a reaction to certain proteins in the grains commonly used to make beer, barley and wheat. The hordein found in barley and the gliadin found in wheat are types of gluten that can trigger symptoms in sufferers of these diseases.