F E R M E N TAT I O N
Natural Beer
Carbonation
Spunding can save a brewery time and money
Submitted by Precision Fermentation
Using a simple spunding valve can
naturally carbonate lagers and ales
without worrying about building
dangerously high pressure.
In order to speed up production,
maintain a natural process, achieve a
certain mouthfeel, follow an interpretation
of Reinheitsgebot or simply spend less
money buying carbon dioxide gas (CO2),
some brewers decide to carbonate their
beer naturally before packaging. This
differs from America’s much more common
“forced carbonation” method of forcing
the proper amount of purchased or self-collected
CO2 into the beer.
As an unregulated natural carbonation
requires a brewer to keep active vigil over
their ferment, lest it develop head or fizz
that’s too fervent or too lackadaisical, this
potentially dangerous technique can leave
too much to chance. As a way to control the
amount of gas absorbed or released, some
brewers turn to “pressurized” fermentation,
otherwise known as spunding.
What is spunding and how
does it work?
Spunding directly translates from German
to English as “bunging.” This method of
natural carbonation involves carefully
monitoring the present gravity and sealing
off the tank after the aggressive initial
stages of fermentation have finished. Once
the wort ferments to near the targeted final
gravity (there are too many variables to
recommend how near) and all orifices are
closed off, the brewer sets the spunding
valve they’ve attached to the tank to
the desired hold-pressure. Although the
pounds per square inch (psi) depend
heavily on the style of beer and the desired
amount of carbonation as well as the actual
temperature of the beer in the tank, this
number will almost always hover in the
single digits so as not to risk exceeding the
safe limitations of the tank.
The valve’s attached gauge monitors
psi (or the display could read in metric
pressure units such as bar or kilopascals),
and any extra gas emitted above the set
level triggers the variable pressure relief
valve to open automatically. Once the
pressure falls back down to the desired
setpoint, the valve closes.
Why should brewers
practise spunding?
“Carbonation achieved via the old, proven
German practice of spunding is one
approach to creating the smallest-possible
bubbles and creamy mouthfeel in beers,”
said Jaime Jurado, production VP at Ennoble
Beverages and past president of the Master
Brewers Association of the Americas. “I am
mystified as to how this might be explained.
There is no apparent technical reason why
my perception of these finer carbonation
bubbles compared to force-carbonation
exists. But vaya con Dios!”
Though the effect is unproven, other
words sometimes used to describe the
bubbles and/or mouthfeel generated by
naturally carbonated beer are: soft, round,
fine, bright and consistent.
One word not likely associated with
spunding is pungent.
Since pressure can suppress the
expression of volatile compounds that
form esters, pressurized fermentation can
suppress unwanted esters from certain
yeasts, leading some advocates to proclaim
that the technique can create clean
“lager-like ales” in less time and at higher
temperatures than it would take to brew an
actual lager.
“You can also cut out the end time
it takes to add CO2,” said Ingrid Epoch, a
brewer at New Jersey’s Eight & Sand Brewing.
Can ales and lagers be fermented
this way?
Most armchair brewers associate spunding
with lagers because the tradition started in
Germany where brewing began long before
CO2 containers could be purchased, and
though German brewers typically consider
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