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
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
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 . 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
. 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
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
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 
|"Ordinary" Bitter||1.031 -
|Draught Mild||1.030 - 1.036||2.5-3.6||29-48%||14-37|
|Best Pale||1.040 - 1.050||4.3-6.6||21-43%||19-55|
|Brown Ale||1.030 - 1.040||2.5-3.6||43-55%||16-28|
|Strong Ales||1.066 - 1.078||6.1-8.4||32-44%||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
- 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
- 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
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
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: firstname.lastname@example.org.
- Malting and Brewing Science, Vol 2, J. S. Hough et al, 1982, pg 688.
- The New Brewer, Vol 10, number 1, Jan-Feb 1993, "Its A Way of Life", by
Alan Pugsley, pg 39.
- Analysis of commercial beers, Malting and Brewing Science,Hough et al,
1982, pg 780.