Talking Tech – Caring for cask in the pub cellar

Earlier this year, we looked at the efforts brewers go to ensure the beer in their casks has enough dissolved carbon dioxide to allow pubs to serve it with the gentle carbonation associated with the format (see here). In this issue, we look at what happens when that cask reaches the pub cellar.

Pubs may buy their beer direct from their local brewers, they may have to source it from their Pub Company landlords, or they may purchase it from a beer wholesaler who supplies beers from many breweries. We will look at how these supply arrangements work in a future issue but the result is that casks may arrive at the pub direct from a brewery a mile away or via a lengthy supply chain.

Cooling the beer to cellar temperature

Once casks are delivered into the care of a pub’s cellar team, the first thing they need to do is give them time to adjust to cellar temperature.

In an ideal world, to keep beer at its very best, it would be stored in temperature-controlled warehouses and delivered to the pub in refrigerated vans. However, such ‘total cold chain’ distribution is rare in the UK. Although casks from a local brewery may have only come out of a cold store a couple of hours earlier, those from further afield may have had a lengthy journey and casks may arrive at the pub at ambient temperature. If a cask is delivered at 20°C and placed in a cellar at recommended cellar temperature of 12 °C , it will take the beer inside the cask over 24 hours to cool to 12°C.


Pub cellars should be meticulously clean places, especially when keeping cask ales which are open to the atmosphere and whatever airborne bacteria it contains. Food has no place in the cellar with dairy products a particular risk – lactobacillus, the natural bacteria which turns milk into yoghurt or cottage cheese, is one of only a few bacteria that is equally at home in beer, but its sour flavours are not usually welcome in your best bitter.

Spillages should be mopped up at once – open beer puddles are the chief route for the spread of wild yeast and bacterial infections. Cellar walls and ceilings should be painted with anti-fungal paint and washed down frequently.

Give it time…

Cask ale needs time to mature and condition (commonly called ‘secondary fermentation’) after it is racked into casks – this is typically anywhere from a week for a simple pale ale to a month or more for a stronger more complex ale. Beer which has not had time to mature will be what is known as ‘green’ – containing off flavours which can mask the true flavour of the beer.

Traditionally, casks would complete most or all of their maturation in the pub cellar, However, many brewers are aware that modern cellars tend to be smaller than those of old and publicans don’t have the space to hold beer for extended periods.

Therefore increasingly brewers will complete most of the conditioning at the brewery – either in tanks before racking or by holding newly racked casks at the brewery before being delivered to customers. However, some brewers still retain traditional methods and will expect pubs to hold casks in the cellar for a week or more before preparing them to be put on sale.

Some pubs have the good fortune to have large cellars where they can routinely have their beers delivered two or more weeks before they expect to need them. Casks rarely indicate how long the beer has been in the cask (more commonly being marked with a best before date rather than a racking date). Therefore the less fortunate cellarman needs to know how his or her chosen brewers condition their beers – only with that knowledge can they rotate the beers in their cellar to ensure those that need time are allowed it.

Preparing for service

Cask ales contain live yeast so to prepare a cask for service, it needs to be placed in its final serving position (be this on its side on a traditional stillage or on its end for modern ‘vertical extract’) to allow the yeast to drop out of the beer before serving. See our earlier piece on casks and kegs for a brief explanation of vertical extraction.

A beer that has been largely conditioned in the brewery can ‘drop bright’ in as little as a few hours, whereas a more traditionally conditioned ale may need 48 hours or more. While some unfined beers may be intentionally hazy, most will still clear in some form or other given time.


An unvented plastic shive

Venting is the process where the seal on the cask (which may be wooden but is now more commonly plastic) is breached to release the pressure which has built up during secondary fermentation. Traditionally the cask is vented through the ‘shive’ – the seal on the hole in the side of the cask where the cask is filled – but with modern vertical extraction, the cask is vented through the ‘keystone’ (in the round end face of the cask) through which beer will also be drawn out.

The purpose of venting is two-fold. Firstly, it allows excess carbon dioxide (CO2) to slowly bubble out of solution until an equilibrium is reached where each pint of beer will contain just over one pint of CO2 dissolved in it – this level of around 1.1 ‘volumes’ of CO2 is the gentle carbonation level associated with good cask ale.

However, the second purpose is to allow purging of volatile substances such as acetaldehyde (green apples flavour) which are generated during fermentation.

Venting must always be delayed until the cask has reached cellar temperature. With the volume of CO2 beer can hold in solution being related to its temperature, to vent a warm beer will result in loss of much of the hard earned ‘condition’. If dissolved CO2 escapes when a beer is warm, it cannot be regained when the beer later reaches cellar temperature.

Vented cask with soft spile

After venting, the cellarman may initially insert a porous soft peg (‘spile’), allowing a lively beer actively generating carbon dioxide (CO2) to breathe – allowing CO2 to escape and reach that soft carbonation level we seek out.
Alternatively, they may go straight to inserting a semi-porous hard-spile, allowing the beer to continue to develop while keeping its condition until the beer is needed.

Even with a hard spile inserted, a cask which has completed secondary fermentation will still slowly loose condition through the spile. There is no hard and fast rule on how long a cask can be kept on hard spile but more than three or four days would be excessive.

The cellarman’s art

Which leads us to the final, but perhaps most important skill of the cellarman – that of timing their own art.

A beer festival knows exactly when their casks are expected to be ready (even if the live nature of beer and the tight timescales they often work in means they can’t always get it exactly right).

By contrast, the pub cellarman can be juggling the maturation and venting of multiple casks, trying to get each to perfect condition at just the time the preceding cask is emptied by their thirsty customers.

With the variety of factors that affect how busy or pubs are – from TV events to the vagaries of the British weather – meaning that casks can sell out in anything from 2 to 72 hours or more, this is no mean task.

When you get that perfect pint – remember the skill that has been involved in getting it there.