What image does your brewery choose to illustrate its beer? For many this will be a pint of ale on a bar, in a drinkers hand or pulling frothily from a beer engine.

In others it may be beer exiting from the brewery or delivering to the pub. If the latter what vessel is shown, cask or keg? For 100% of UK breweries I would bet casks are well to the foreground, even in larger SIBA producers.

In this view cask is the epitome of craft brewing. Traditional, solid and reliably historic the image of a cask says: “ This is beer as perfected over centuries, no high tech input, just skilled down to earth goodness. Drink me now to share in the delight”. The message is even better if the casks are wooden but stainless steel still carries the impression and generates the salivation.

Kegs, in contrast proclaim the intrusive finger of technology, of high pressure fizz and, due in no small part to high pressure consumer campaigning, vile flavours and evil intentions.

The truth of all this depends on your preconceptions and doesn’t always hold up in the clinical conditions of a blind tasting of the same beer dispensed from the two containers. Moreover, what of new and novel beers which may have advantages from keg technology? Do kegs intrinsically degenerate beers or could some be suited to their form? The interest of some brewers in adopting keg technology suggests that they may have advantages. If so then what?

To objectively compare cask and keg it is necessary to separate the processing which is commonly but not essentially associated with keg – filtration and pasteurisation. Big brewery production uses kegs as a convenient vessel to hold filtered or pasteurised beer because they can be filled easily without contact with air and don’t have unhygienic closures of wood and plastic. As a result sterile, bright and brewery carbonated beer can remain sterile for weeks and be easily connected in the pub without the need for yeast settling. As such they are ideally suited to mass production and rapid processing.

They are also suited to small brewery beers which are also filtered if the brewery wishes to produce specialist styles such as continental lagers, stouts and a wide variety of international beers traditionally served in such a manner. Keeping such beers sterile and away from air is essential and difficult to achieve in a cask. More complex filling, and cleaning, systems will be needed with kegs but are not impossible.

However, this doesn’t mean that kegs can’t be used for beer containing yeast. Kegs contain two openings within their central boss. The inner draw tube allows beer to be pushed out of the cask while the surrounding sleeve is connected to a gas inlet. This typically receives CO2 under high pressure to push the beer out. However, it can just as easily be left open to allow air into the keg while the beer is pulled out by a beer engine in the same was as from a cask. Despite their different connections casks and kegs are just vessels.

A more pertinent issue is whether kegs would allow cask ale to undergo secondary conditioning. Again being just a vessel there is no reason why it shouldn’t. Kegs can be filled through the central spear and sealed before dispense. Carbonation can develop during storage and be released from the gas inlet by venting. They do in fact have a major advantage in being easy to flush with CO2 or mixed gas before filling so minimising the potential for oxidation and staling.

Filling against a gas blanket shouldn’t be an infringement on cask ale. Most large breweries and many others do this with casks anyway. A more protective procedure would be to couple the gas input line to a demand valve in the cellar. This device allows CO2 or mixed gas into the keg (or cask) as a strict replacement for beer removed and so again limits oxidation and staling. Although contentious to purists the carbonation in the beer still results from yeast activity and doesn’t compromise the purity of cask ale being beer containing active live yeast.

So far kegs can be regarded as simply different shaped vessels for cask ale to conduct its traditional action of secondary fermentation. Perhaps the major difference in effect on cask beer is a result of their shape rather than their dispense system.

Casks are cask shaped to allow yeast to settle in their belly and not in the tap. This maximises the volume of clear dispensed beer. With a small area for settlement this compresses the sediment so minimising the potential for resuspension if the cask is disturbed. In a keg the sediment will be spread across the base of the vessel and be more easily drawn into the outflowing beer.

While this is a reasonable hypothesis it is also subject to a number of influences which may overlap cask and keg effectiveness. Yeast sediment volume depends not only on cask geometry but yeast strain, yeast concentration, fining dosing and effectiveness, age and character of the beer and possibly another dozen other features we fight to control from gyle to gyle. Cask geometry is no guarantee of clarity. Beer is commonly dispensed from upended casks via siphons and numerous experiments show kegs to be equally effective in delivering clear cask conditioned beer. In fact a coarse filter on the outlet sleeve can reduce the yeast removed.

As long as external pressure is not applied to keg beer there is no reason it cannot perform as well as cask dispense. Add pressure, however, and there will inevitably be differences – although not necessarily negative. Carbonation is accepted as a major factor in beer quality and a lightly carbonated keg beer is likely to be better received than a flat cask pint. However, we are straying out of the accepted criteria for cask ale and a more highly carbonated keg beer will alter character considerably.

Whatever the technical reasoning for choosing cask or kegs for dispense the choice for many of us is often still due to image. The cask at rack or the cask on dispense capturing far more of brewing romance than a keg and flowjet valve. That said it hasn’t taken long for plastic casks to be accepted as another feature of technical progress so perhaps the keg does have a future, if only in the background of your deliveries.


Written by Dr Keith Thomas
Brewlab Director

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