What's the difference between cask and keg?

The range of beers on our pumps and in our tanks has expanded in recent years, ranging from our traditional real cask ales to the kegged modern craft beer.

But what is the difference between cask and keg beer? We turned to renowned beer writer Phil Mellows for help.

I was in a pub once (to be honest it’s quite a frequent occurrence) and a customer asked the barman what the difference was between cask and keg beer. The barman thought a moment before confidently answering.

“Cask beer comes out of these,” he said, pointing to a handpump, “…and keg beer comes out of these,” gesturing towards the lager taps.

It would be interesting to know how many people could tell you more than that. Handpumps are a great symbol of the traditional English pub, and of cask conditioned ale, and signify the special bond between the two. Discriminating pub-goers are reassured by a wicket of handles on the bar, even if they’re not going to order the cask.

Yet handpumps are little more than a means of getting the beer up from the cellar and into the glass, and they aren’t even the only way of doing that. When I started drinking in the 1970s, a lot of cask beer was poured by electric pumps. And there are still pubs that specialise in serving it straight from the barrel.

Handpumps also provide advertisement and theatre, but they don’t define cask. They are merely a superficial feature denoting the presence, hopefully, of something interesting and distinctive beneath the bar.

What is cask ale?

Cask is also known as ‘real ale’, of course, but that’s not really helpful. ‘Living beer’ would be more accurate, since cask beer is rare among products in that it arrives at the retail outlet unfinished. The yeast, the weird little creatures that ferment the beer by consuming the sugars in the malted grain and expelling alcohol and carbon dioxide in the process, continue to munch away down there in the cellar, giving character to the beer in a process known as ‘conditioning’.

For this to happen properly, it has to be at the correct temperature – between 10 and 12 degrees C, and the publican and their staff have some quite skilled work to do. Like good comedy, the secret is timing. After leaving the cask at least 24 hours to settle it is ‘vented’. Enough air is let in to encourage the beer to carbonate – but only just enough before resealing it with a little peg called a spile.

This is the crucial moment, and there is as much art as science in getting it right. The result should be a beer in the glass that is cellar-cool and naturally, thanks to the yeast in the cask, gently sparkling. Don’t let anyone tell you cask is warm and flat. If it was a wine, they’d call it ‘pet-nat’.

The other key player in creating perfect cask is the drinker. Once the first pint is poured the whole cask must be consumed within three days. A pub that’s known for keeping its beer well will attract cask drinkers, which in turn ensures the cask is emptied quickly.

It’s a virtuous circle that companies, like Fuller’s, that know and care about cask beer, benefit from, and it makes possible a wider range on the bar that, in turn, gives cask drinkers more reasons to visit.

Fuller’s pubs this autumn, alongside familiar names such as London Pride, Dark Star Hophead, ESB and HSB, and the seasonal Red Fox, will also have on the pumps a new IPA from Hophead called Starlink, the latest 2024 Vintage Ale and a special collaboration brew with Berkshire craft brewer Siren.

So what are you waiting for? Come and help keep that cask beer fresh!