WORT AERATION PRIOR TO PITCHING
Aug 14, 1993
There has been a great deal of enthusiastic reporting on the
use of aquarium air pumps to aerate wort prior to pitching
yeast and many rather preposterous claims of shortened time
to the onset of fermentation resulting from the use of same.
As the author's experience on one batch did not support any
such claims, a controlled experiment was designed to
determine the validity of said claims.
The experiment described herein compares the air pump
aerator with several other less exotic methods along with an
un-aerated control batch.
The wort used was withheld from a batch of Pilsner style
beer with a gravity of 1.050. It was re-boiled several days
after the original batch was pitched so that it could be
pitched with controlled amounts of kraeusen from the new
batch. The re-boiling was to re-established an anaerobic
environment along with re-sterilizing the wort.
Prior to pitching, the wort was divided into (4) 500 ml
samples in sterile, one quart mason jars and aerated in
various ways as follows:
The wort was cooled to a temperature of 70F before being
aerated. All four samples were pitched with 50 ml of
working kraeusen. This active wort was taken as a single
sample and thoroughly mixed prior to dividing into 4
individual portions to assure a homogeneous and identical
yeast in each test.
- #1 Control... No aeration. Just gently poured from kettle
- #2 Siphon Simulation... Poured into jar from a height of
12 inches in a narrow stream to simulate what one would
get simply by siphoning and letting the stream fall
into a fermenter.
- #3 Pumped from kettle through nozzle to "squirt" into jar.
This is the system normally used by the author to
transfer from kettle to fermenter.
- #4 Aerated with aquarium pump and fine mist airstone.
Pump was run until foam volume equaled wort volume then
shut off till the foam collapsed. This was repeated 5
times for a total on-time of (2) minutes. The time was
based on a very conservative scale down from Miller's
suggested time of 15 minutes for a 5 gallon batch. It
represents about 5 times the amount of air per unit
wort volume recommended by Miller. (*1)
The yeast used was Pilsener Urquel recultured from a slant
obtained from Paul Farnsworth. (*2)
After pitching, the four test batches were placed in a
refrigerator at 40F and checked every four hours for signs
of incipient fermentation.
No sign of fermentation was detected until the 72 hr check.
At this time, a small island of bubbles was just visible in
the center of all four samples.
To accelerate the conclusion of the experiment, the samples
were removed from the refrigerator and allowed to rise to
room temperature (75 F). They were monitored until the
entire surface of the fermenters were covered with foam.
This occurred about 9 hours later on all four samples.
To take the experiment one step further, a similar but
abbreviated experiment was conducted with ale yeast.
Two 500 ml samples of a similar wort were treated as
Both samples were pitched with 0.4 grams of granulated EDME
ale yeast, poured directly on top of the wort.
- #5 Control... No aeration
- #6 Shook jar vigorously until foam volume equaled wort
volume. This was allowed to settle and repeated
They were maintained at a temperature 75 F and monitored
regularly until the onset of fermentation. This occurred at
4.5 hrs in both samples. The tops of both fermenters were
covered with foam at 10 hrs total elapsed time.
The experiment seems to confirm the author's previous
experience and points to the conclusion that the method of
aeration used has no correlation with or effect on the time
to onset of fermentation. Contrary to frequently stated
anecdotal experience, the un-aerated control samples started
fermenting as soon and with the same vigor as the variously
aerated samples. This was true both in the case of cold
temperature lager yeast and room temperature ale yeast.
This experiment was not intended to test any other aspects
of the brewing process that may be affected by wort
aeration. Much has been written on the subject and the
present author's intent was only to study the effects of
aeration on the onset of fermentation.
- *1 Dave Miller on Hung Fermentations,
- *2 Dr Paul Farnsworth, Scientific Service, San Antonio, TX.