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Oppaat:Real ale:Cask ales by Jim Bush

England has numerous distinctions to contribute to the brewing world, but none is as unique and important as the tradition of cask conditioned ales. Cask, or Real Ale as it is often called, is a special brew, served in a special manner, by hand pump from the cellar. Despite what you may have been told in the US, cask ale is not warm and it is not flat. It is dispensed at cellar temperatures, 54 - 59F, and is naturally, albeit lightly carbonated. As a result, the mouthfeel of the product is extremely distinct from that of a "gassy" keg beer.

Temperature and carbonation have a great impact on the perception of the beer on the palate, and the combination of the cellar temperature, low CO2 volumes, and often a snappy hoppy aroma & flavor, all are blended in the mouth to reveal a distinctly different and satisfying ale. While the spectrum of cask ales can be difficult to generalize, the carbonation, temperature, hoppiness and fermentation products are usually dominant factors in the flavor perceptions of all cask ales. Many cask ales have numerous fruity notes that are created in the fermenter and gradually reduced and blended during the maturation and conditioning periods. The important point is that they are supposed to be there, and that they manifest themselves in varying degrees of complexity throughout the life of the cask. This is one of the wonderful aspects of cask ale, it is living, breathing beer that will change over the week or so between bunging of the cask and the final pull of the hand pump.

Production of Cask Ales

Cask ales produced in England are top fermented beers, often produced in open fermenters. Open fermenters are just what they sound like, a vessal without a top. Often the fermenters are a large cylander with a hinged lid. Many are attemperated (chilled) by piping that is submersed in the fermenting wort. Either chilled water or chilled glycol is pumped through the piping, allowing the brewer to control the rise of temperature during the fermentation.

While closed tanks are used in some of the bigger breweries, open fermenters are the traditional technique, and some noted breweries rely on the old Burton Union and Yorkshire Squares systems of open fermentation. Both of these subsets of open fermenters are designed so that the fermentation effluent or krausen is allowed to flow out of the fermenter, into a collection area, and either removed or allowed to return into the main fermenter. This technique tends to introduce added oxygen to the fermenter that will often result in slightly elevated diacetyl levels in the beer. This is generally not a negative aspect of these beers. The use of open fermentation may seem strange to brewers who go to great lengths to keep out airborne contaminants, but this is not a worry in English brewing.

Like all brewers, English ale brewers are very careful to sanitize everything that comes in contact with the cast out wort, especially as the wort drops below 170F. A clean and sanitized fermenter, in conjunction with clean healthy yeast pitched with a cell content of between 6-12 million cells per ml will ensure a rapid start to fermentation, and the subsequent production of vast amounts of CO2 which will blanket the fermenting wort, and thus protect the beer from airborne contaminants.

Once the fermentation is active, the pH of the beer will be dropping rapidly from an initial level of 5.4 down to the mid 4 range, and with some strains as low as 4.1. This acidulation of the wort, in conjunction with the large production of CO2 results in an environment quite unhospitable to most airborne bacteria. The key, as with all brewing, is to pitch an adequate amount of healthy clean, cultured yeast slurry.

In open fermenters, the brewer must skim the yeast head off the beer between days 2 and 3 of normal ferments. Often, the trub that rises to the top after day one is removed to reduce particulate matter that can lead to astringency problems. The use of open fermenters provides an easy method for the observation and skimming requirements of top fermented ales. With typical top fermenting strains, healthy white yeast is cropped off during day 3 or 4 of fermentation and stored for reuse. Yeasts collected from healthy ferments can be repitched for hundreds of generations provided the brewery is clean and the brewer is acutely noting fermentation performance. Any degredation in yeast performance should be corrected by replacement of the strain with fresh stock.

Fermentation is usually complete within 5-7 days at 60-70F. At this time, the beer is racked into maturation tanks where it can sit for a brief conditioning period. Alternatively, the still beer may be racked directly into the cask. The important point is that the transfer is done with approximately one degree Plato (1.004) of residual extract left in the still beer, and between .25 - 2 million yeast cells per ml of still beer [1]. The residual extract may also be supplied in the form of priming sugars. This is accomplished by preparing a solution of brewers sugar (glucose) at a specific gravity of 1.150 (34P) and adding to the cask at a rate of .35 to 1.75 l/hl. Cast out wort as well as krausen beer can be used, but in the latter case, excessive yeast cells may interfere with the clarification in the cask.

As the casks are filled, a fining agent is added to the vessel, usually in the form of isinglass in quantities of 1-5 litres per UK BBL [2]. Isinglass is composed of collagen molecules which carry an overall positive charge. Since yeast will exhibit an overall negative charge, an electrostatic attraction will result, leading to clumping of yeast & isinglass particles and then sedimentation. The process of clarification requires about a day to result in a "star brilliance" to the beer [3]. Beers with residual yeast levels of 2 million cells per ml or above will be more difficult to clarify. Many brewers also add whole hops at a rate of 1/2 to 3 oz/BBl at cask filling time. With the advent of modern packaging in vessals like polypins some brewers are using hop oil extracts to mimic some of the character found in cask hopped ales. At this point, the cask ale is ready for transport to the publicans cellar.

Maturation of Cask Ales

After the cask is shipped to the local pub, it is no longer the direct responsibility of the brewer to finish the conditioning job. This task falls onto the publican/cellarmaster. In the old days, it was the cellarmasters duty to add the finings to the casks as they arrived from the brewery, but this is not common today. Once delivered to the pub, the cask is placed onto its stillage, and allowed to sit for 2-3 days. During this time the cask is udergoing the secondary fermentation in the cask, or cask conditioning.

One day prior to serving, the cask must be prepared for dispense. This is done by driving the hard spile (non porous wood peg) into the shive (round plug device on top side of cask, this would be equivelent to a bung on older US kegs). The spile is essentially a primitive CO2 valve, a nonporous one is used to close the cask for overnight storage while a porous spile is used during dispense to allow a path for air to enter the cask, allowing the beer to be pulled by the beer engine. When the spile is first hammered into the cask, the cellarmaster allows the CO2 to vent from the cask, preventing CO2 buildup levels that would not be welcome to real ale lovers.

The final step in tapping the cask is to drive the tap into the keystone (actual port through which the ale is "pulled"). A minimum of one day settling is required to ensure that the tapping process did not disturb too much yeast. The next day, the cellarmaster will sample the beer to determine when it is ready. This is an extremely important part of the process and a major reason why many cask ales are not served at their peak of flavor. Some beers require a little more time than others to reach their peak.

Dispense of Cask Ales

When the cellarmaster has determined that a new cask is ready for dispense, the beer line connecting the cask and the beer engine are connected. A beer engine is merely a fancy hand pump that "pulls" the beer out of the cask. As beer is removed from the cask, air bleeds in through the porous spile. It is for this reason that cask ales are best during the first few days of dispense, and are known to become increasingly undrinkable after about day 3 or 4. Oxidized beer in any country is not very pleasurable, and casks allowed to sit for too long exhibit a strong oxidation effect.

In an effort to combat some of the ill effects of oxidation, brewers and publicans have devised several methods of introducing CO2 into the cask. The least objectionable is the blanket CO2 method whereby an extremely small amount (1-2 psi) of CO2 gas is pushed into the cask. Since CO2 is heavier than air, it will form a "blanket" over the beer, protecting it somewhat from the oxygen.

Another method makes use of actual CO2 tanks to push the beer out and mechanical pumps are also in use to help pull the beer from the cask. Traditionalists despise all methods of CO2 use to help preserve the beer quality, arguing that all result in some form of "gassy" ale.

The campaign for real ale (CAMRA), is particularly adamant about only dispensing real ale by the use of a beer engine without blanket pressure. To this end, they refuse to list pubs that employ CO2 systems in their excellent book, CAMRAs Good Beer Guide, published annually. While CAMRAs dedication to tradition is admirable, it may be unrealistic to expect the smallest pub in the furthest region to be able to adequately care for cask ales in the same fashion that the busier pubs can.

If cask hopping is employed, a small strainer device is used to keep the hops in the cask, and out of ones glass. At the tip of the dispensing nozzel, a sprinkler attachment is used to force the beer through several small holes, resulting in a release of carbonation into the beer and glass. This results in a thick head and is similar in principal to the tap design used by Guinness.

Cask ales can also be dispensed directly from the cask using gravity. In this arrangement, a cask is positioned so that the beer outlet is pointing down, and merely by opening the spigot and allowing an air vent, the beer will pour out of the cask by gravity flow. If a soda keg is employed in this technique the liquid dip tube would need to be removed or severely shortened. If the beer is to consumed in one evening, it is an excellent method of dispensing quality beers.

Brewing Tips for Home Production of Cask Conditioned Ales

The production of cask conditioned ales is not that different from the normal production of homebrew. In both cases, the beer is naturally carbonated in a closed vessal. The major difference is in the amount of carbonation that is developed, typical ales and lagers are conditioned to about 2.5 Volumes of CO2, while cask ales are closer to 1.5 - 1.75 volumes. When brewing cask ales, there are two methods to follow:

Let the fermentation complete, and add a small amount of fermentables in the cask.
Carefully monitor the fermentation and when the gravity is within 1 degree Plato of the terminal gravity, bung the cask. This method is preferred but can be difficult due to the requirement that the brewer know fairly accurately what the real terminal gravity will be. This technique is simplified by using SS soda kegs for dispense, and carefully venting excess pressure as the cask conditions.

The use of finings for the homebrewer can be an additional effort that many may not want to bother with. In this case, be sure to use a yeast that is known to be an excellent flocculater. If cask hopping is done, only fresh whole hops or whole hop plugs should be used. Place the hops in a permeable bag, using a sanitized weight to force the bag to the bottom of the cask. If you intend to serve the beer as true cask ale, a gravity feed can be employed but ideally, the cask should be emptied in one night.

A Brief Description of Styles [4]

TypeOriginal GravityABVUnfermented
"Ordinary" Bitter1.031 - 1.0453.0-4.627-45%20-40
Draught Mild1.030 - 1.0362.5-3.629-48%14-37
Best Pale1.040 - 1.0504.3-6.621-43%19-55
Brown Ale1.030 - 1.0402.5-3.643-55%16-28
Strong Ales1.066 - 1.0786.1-8.432-44%25-43

Historically, IPAs were of much higher OG, but my experience has found that today, these are as low as 1.035 up to 1.045, and merely a hoppier version of Bitter. Strong ales today are often found as "low" as 1.051 OG but frequently in the 1.062 range.

Note that despite the relatively low alcohol by volume (ABV) of all but the strong ales, these beers have a lot of unfermented matter that gives the cask ales abundant body and mouthfeel.

Unfermented matter is primarily composed of dextrins, which normal yeast cannot metabolize, and as such the dextrins will carry over into the finished beer intact. The use of caramel malts (or crystal malt as it is often called) will always increase the quantity of unfermentable matter in a beer and caramel malts are routinely used in the production of cask ales. Many brewers create a wort of OG 1.055 or higher and dilute this into the fermenter by adding boiled and cooled water to result in the 1.035 OG. By using this technique, a degree of carmelization can be achieved from the kettle processing that may result in beneficial flavor attributes.

Glossary of terms

Burton Unions
Classic fermentation technique that recirculates the yeast overflow from the fermenter into a collection tank and back into the fermenter.
A fining agent made from the processed swim bladders of fish, primarily the Sturgeon fish.
Fining agents
Materials that help to clarify cask conditioned ales. Includes isinglass, geletin, and in the case of protein removal, Alginol (negatively charged polysaccharides).
Residual extract
Not to be confused with terminal gravity. Residual refers to the amount of fermentables remaining at a certain time, these fermentables will be metabolized by the yeast in suspension, given time to do so.
A wooden device used to prop up and hold the cask in position for dispense.
Terminal gravity
the final gravity of the beer. It is measured after all of the fermentables are consumed.
Top Fermented Beers
beers fermented using a top fermenting yeast strain, S. Cervesae. Yeasts of this class tend to ferment the wort through action near the top of the fermenter, and also tend to rise to the top at the fermenter at the end of fermentation.
Unfermentable Matter
primarily dextrins which normal brewers yeast cannot metabolize. As a result, these body builders are carried over into the finished beer and contribute sweetness, body and mouthfeel. It can roughly be calculated by reading the terminal gravity. A beer that has an OG of 1.040 and a FG of 1.010 has 10/40 unfermented matter, or 25%.
Yorkshire Squares
Classic square fermenters, made of slate at the Samual Smith brewery. Consists of a slate bowl device that is situated above the fermenter allowing yeast overflow to collect for removal or if left, re- introduction into the fermenter.

About the author

Jim Busch is an electrical engineer developing firmware under contract for NASA, at the Goddard Space Flight Center in Greenbelt, MD. An avid brewer since 1988, and an all grain brewer since 1989, Jim can often be found in his backyard brewery that he designed and built with Keith Harper in 1992. Jim can be located on the Internet at: busch@daacdev1.stx.com.


  1. Malting and Brewing Science, Vol 2, J. S. Hough et al, 1982, pg 688.
  2. IBID.
  3. The New Brewer, Vol 10, number 1, Jan-Feb 1993, "Its A Way of Life", by Alan Pugsley, pg 39.
  4. Analysis of commercial beers, Malting and Brewing Science,Hough et al, 1982, pg 780.

Jim Bush /  31.8.1997

17.1.2022 19:10


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