Dealing with beer haze
part two
Having looked at
non-microbiological hazes in part one of this article I will now look
at hazes caused by microbes and how to avoid them.
Microbiological hazes
can be caused by an excess of brewers’ yeast remaining in
suspension or a bacterial and/or wild yeast infection. To prevent
your own yeast causing problems the first step is to ensure that it
is in a healthy state and the correct amount is pitched into the
wort. For a beer with a gravity of 1.040 around 10 million viable
cells per ml of wort will be required. You will need a microscope to
do a yeast count and methylene blue stain to determine viability.
Inexpensive microscopes are now widely available and with only a
little practice they become easy to use and should become part of
your routine. If weighing yeast slurry you will be looking for around
2lbs/bbl or 450g/hl. Yeast counts should also be carried out on beer
before packaging. For cask beer it is recommended that the yeast
count at racking is 0.5 to 2 million cells/ml.
Good flocculation will
get the yeast out of suspension and there are a few things you can do
to help it on its way. Calcium is needed for yeast to flocculate so
get your liquor treatment right. Auxiliary finings and isinglass
finings will both greatly help beer to clarify. Auxiliary finings are
negatively charged and using them before adding isinglass, for
example in the fermenter, will help the isinglass work well.
Isinglass finings have a positive charge and will attract the
negatively charged yeast cells and help them settle out. Both these
types of finings will need to be used at an optimised dose as under
or over fining will give poor results. Your finings provider should
be able to help you with finings optimisation if you are unfamiliar
with the procedure.
Microbiological hazes
can also be caused by infection of bacteria and/or wild yeast. A
microscope can be of use in detecting infection, but only if the
organisms are present in sufficiently high numbers and further
lab-based tests may be required for certainty and to confirm
identification.
Using selective culture
media grown under specific conditions (aerobically or anaerobically)
allows the numbers of organisms present to be determined and
identification is easier when looking at the shape of the colonies.
Culturing for microorganisms will not give an immediate result as
they will take days to grow, but can be very useful both when trouble
shooting and as part of a quality assurance programme.
A table of which
organisms to look for in different samples is shown below:
Sample type
|
Microorganisms
|
Wort
|
Aerobic + anaerobic bacteria, wild yeast
|
Yeast
|
Aerobic + anaerobic bacteria, wild yeast
|
Green Beer
|
Anaerobic bacteria
|
Bright Beer
|
Anaerobic bacteria
|
Filtered Packaged Beer
|
Anaerobic bacteria
|
Cask Conditioned Beer
|
Aerobic + anaerobic bacteria, wild yeasts
|
As can be seen there
are many stages at which micro problems can occur and avoiding them
requires an integrated approach. Brewery design should minimise
chances of cross contamination e.g. keeping malt dust away from
fermentation areas. Pipework should avoid dead legs to prevent
material that will support microbial growth accumulating and to
ensure that cleaning cycles are effective. Plant integrity should be
checked regularly and any leaks or perished seals are warning signs
of potential problems.
Checks can be made for
microbial contamination that give an immediate result. ATP
bioluminescence detects a compound found in all living cells and is
an excellent marker for microbial organisms. Swabs can be used to
check that surfaces have been cleaned effectively and last rinse
water at the end of a cleaning cycle can be monitored.
If infection is found
in packaged beer then corrective action can only be used to prevent
it reoccurring in future brews. But if bacterial infection is found
in one if the most common sites, pitching yeast, then acid washing
can be used to remedy the situation almost immediately.
Acid washing will
significantly reduce bacterial numbers without greatly affecting the
health of the brewing yeast if carried out correctly. The yeast must
be at a cold temperature before acid washing and it must be kept cold
during the process. Slowly add acid (typically 75% food grade
phosphoric diluted 1 in 10) to the yeast slurry whilst mixing well
until the pH has dropped to between 2 and 2.2. Leave for one hour,
stirring regularly, and then pitch immediately. Unfortunately if the
pitching yeast is contaminated with wild yeast acid washing won’t
help and fresh yeast will need to be obtained.
Regular monitoring of
process samples as part of a quality assurance programme is the best
way of preventing microbiological hazes in your beer and finding out
if there are any particular problem areas in your brewery.
proper craft that. give you £6 a third for it.
ReplyDeleteIf I sold it for any less I know you'd only feel bad and want to send a voluntary contribution to the brewery.
DeleteWhat is inexpensive in microscope terms? How many thirds of awesome murky would I need to sacrifice?
ReplyDeleteYou can get one for less than £200. It won't be great at that price but it will do the job.
Delete