Beer Contamination Testing

By Kory Davis
QC & Propagation Specialist
The Brewing Science Institute

Not only is beer delicious, it has also been pivotal for mankind’s survival. Due to beer’s inherent antimicrobial properties it was primarily drank when water sources were impure. Beer contains alcohol as well as compounds from hops that keep it pathogen free. This, however, does not mean that beer is spoilage free. There are organisms that can survive in beer that will alter flavor characteristics. These organisms fall under the categories of gram-positive bacteria, gram-negative bacteria, and wild yeast. A few of the recognized bacterial organisms found are Acetobacter, Gluconobacter, Pectinatus, Megasphaera, Zymomonas, Lactobacillus, and Pediococcus. A few recognized wild yeasts are Brettanomyces, Candida, Pichia, Zygosaccharomyces, and Schizosaccharomyces. Common spoilage indicators for these organisms are reduced pH, haze/turbidity, pellicle formation, increased attenuation, and unpleasant off flavors (Bokulich & Bamforth 2013).

To begin contamination testing for these organisms the investigator must first have an idea of what to look for and generally that is determined by the type of spoilage that has occurred. If it is not 100% apparent, then the investigator can begin by looking at the substrate in question under the microscope. Once an idea about what the organism could possibly be, the substrate is plated onto various types of media to confirm its identity. HLP, WLD, LMDA, LCSM, SMMP, and LWYM are a few of the types of media utilized by industry professionals (Committe 2011). After plating, further identification via gram staining or molecular methods can be used to pinpoint what the spoiler is. Usually, however, molecular methods are not necessary if the investigator has enough experience to determine what genus the organism belongs to solely with the use of media. If a species identification is needed than molecular methods will be necessary.

In addition to beer spoilers there is also the category of wort spoilers. A common wort spoiler found is Enterobacter. Enterobacter is a genus of gram-negative bacterial rods found usually only in wort because they generally cannot tolerate the environmental conditions of beer. Common spoilage indicators for these bacteria are increased levels of DMS (cooked corn), as well as other vegetal aromas (Bokulich & Bamforth 2013. MacConkey agar is a common type of media utilized for culturing these bacteria.

Got spoiled beer? BSI offers identification services, for assistance please don’t hesitate to give our QC specialists a call at, 719-482-4895 x 3, and for details on beer testing check out our website at

Bokulich, N. A., and C. W. Bamforth. “The Microbiology of Malting and Brewing.” Microbiology and Molecular Biology Reviews, vol. 77, no. 2, 2013, pp. 157–172., doi:10.1128/mmbr.00060-12.
Committe, Asbc Technical. “Differential Culture Media.” ASBC Methods of Analysis, 2011, doi:10.1094/asbcmoa-microbiologicalcontrol-5.