Dealing with beer haze part two

Though some brewers are now actively encouraging beer hazes, to the extent of doing daft things like adding flour, most beer is still served bright. Following on from this article I wrote for the SIBA journal here's part two.

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.