Real ale served from a cask and how it differs from keg beer

What makes it real ale

Real ale, or cask conditioned beer, leaves the brewery unfinished. It goes into the cask unfiltered and unpasteurised, with live yeast and usually a little priming sugar. In the pub cellar, that yeast ferments the sugar and carbonates the beer naturally. This is called secondary fermentation, or conditioning.

The term real ale was popularised by the Campaign for Real Ale (CAMRA), founded in Britain in 1971 when traditional cask beer was losing ground to keg. The style is still most at home in British pubs. Most cask beers are bitters, pale ales, milds, porters and stouts, often at a modest 3.5 to 4.5% ABV, built to be drunk in pints over a long evening.

The cask and the cellar

A traditional cask has two holes. The shive, on top, takes a wooden or plastic peg called a spile. The keystone, near one end, takes the tap. A common size is the firkin, nine imperial gallons or about 41 litres.

When a cask arrives, the cellar keeper sets it on its side to rest so the yeast can settle. Finings, often isinglass made from fish swim bladders, help pull yeast to the bottom so the beer runs bright. The keeper then vents the cask through a soft, porous spile to release excess gas, swapping to a hard spile once the condition is right. Cask beer is usually kept at about 11 to 13 °C. That cellar work is a skill. A cask that is rushed pours cloudy and yeasty.

How it differs from keg

• Gas. Keg beer is carbonated at the brewery and pushed out with carbon dioxide or mixed gas. Cask beer gets its gas from the yeast in the cask and is drawn up by hand.
• Carbonation. Keg beer often sits around 2.2 to 2.7 volumes of carbon dioxide. Cask beer is softer, often around 1 to 1.5 volumes.
• Temperature. Keg beer is served cold, often 3 to 7 °C. Cask beer is served at cellar temperature, cool but not chilled.
• Filtration. Most keg beer is filtered and often pasteurised. Cask beer is neither, so it is still alive.
• Life. A keg stays sealed and lasts weeks once tapped. A cask lets air in as beer is drawn and is usually best within about three days of being opened.

The handpump and the sparkler

Cask ale is usually pulled through a beer engine, the tall handpump on the bar. Each stroke draws beer up from the cellar by suction. No gas is added. Some pubs serve straight from a cask on the bar by gravity, which is simpler still.

Many handpumps can be fitted with a sparkler, a nozzle with small holes that churns the beer as it enters the glass. That gives a tight, creamy head but knocks some aroma and carbonation out of the beer. Pubs in the north of England often prefer the sparkler. Many in the south pour without one. It is a long running argument with no right answer, only preference.

What it tastes like

Because cask beer is warmer and less fizzy, malt and yeast character come forward. Bread, biscuit, caramel, gentle fruit from the yeast and earthy or floral English hops all show more than they would in a cold, sharply carbonated keg beer. The texture is soft and round rather than prickly.

People expecting an ice cold lager sometimes call it flat and warm. It is neither, when kept well. It is lightly sparkling and cool. Good cask ale is a lesson in how much carbonation and temperature hide in other beers. Our guide on how carbonation changes the taste of beer explains the mechanism.

Why it is rare in India

Cask ale needs a cellar at 11 to 13 °C, careful handling, a pub that sells a firkin within about three days and drinkers who know what to expect. In much of India, where ambient temperatures run well above 30 °C for months, keeping a cask at cellar temperature takes a dedicated cold room. A cask left warm turns sour or vinegary fast.

Some brewpubs try it now and then, often with a small cask or a beer engine fed from a cooled tank. If you find one, order a half pint and taste it slowly. It is one of the clearest ways to understand how serving changes beer.

Signs of a well kept pint

A good cask pint is clear or nearly clear, unless the style is meant to be hazy. It smells fresh, with no vinegar or sour edge. It feels lightly lively on the tongue and is cool, not warm. A tired cask tastes flat, sour or cidery, often because it has been open too long. Our guide to signs of a badly kept pint covers what to say if you get one.

Your first step

Next time you are in a pub or brewpub with a handpump, ask how long the cask has been on and order a half. Taste it next to a keg beer of a similar style and write down three differences. That comparison will teach you more about carbonation and temperature than any chart.

Common questions

What is the difference between cask and keg beer?

Cask beer is conditioned in the cask, unfiltered and served by hand pump without added gas at cellar temperature. Keg beer is carbonated at the brewery, usually filtered and pushed out with gas at a colder temperature.

What temperature is cask ale served at?

Usually about 11 to 13 °C, which is cellar temperature: cool but not chilled.

How long does a cask of ale last once opened?

Most casks are best within about three days of being opened, because air gets in as beer is drawn.

Is cask ale flat?

No. It is less carbonated than keg beer, often around 1 to 1.5 volumes of carbon dioxide, which gives a softer, gentler sparkle.