Big brewing science for small beverage producers.
March 24, 2023

Microbial spoilage in beverages

Why spoilage happens

With an estimated trillion species of bacteria, yeasts and other microbes, how on earth do we determine the risk of microbial spoilage in beverages?

This depends on the product and the process stage. For beer, from the moment the wort is brewed, the organisms capable of growing at each process stage narrows. This is because of environmental factors that present barriers to different microbes. Low pH, ethanol, hop iso-alpha acids, lack of nutrients (particularly FAN and sugar) and even carbonation present barriers.

As the cost of spoilage increases during fermentation, the relative probability decreases. That is, until you hit the packaging line, where roughly half of contamination occurs.

Thankfully, there are limited groups of bacteria and wild yeasts capable of spoiling finished beer. We detect these using microbiological plating, forced spoilage and DNA detection methods, each of which has advantages and disadvantages. For comprehensive coverage, and to minimize false alarms, a combination of all three is best. And don’t forget about sampling bias: the likelihood of missing a positive hit because we didn’t test enough samples.

All-encapsulating microbiological coverage that prevents distribution delays is achieved by combining microbiological methods on multiple samples with forced spoilage experiments.

Non-alcoholic products or non-beer alcoholic products typically spoil more easily. Even just removing hops from a beer opens huge potential for microbial spoilage in beverages. Removing ethanol has a similar effect. Fortunately, low pH is enough to stave off most illness-causing microbes… but ask the person with an exploded can in hand if re-fermentation of beverages is dangerous!

Reading the data

When we grow microbes on petri plates, they multiply over and over until a single cell becomes a colony – visible to the naked eye. We present the data as colony-forming units or CFU. This is an approximation of the number of viable (living) cells that were present in the initial sample at a given concentration, like CFU/mL. Because two cells might grow together as one colony, we can’t say exactly how many viable cells were present initially.

By growing the cells on specialized media that selects for the growth of certain organisms, we determine the potential for spoilage. We always want to see zero-counts, but we can also determine if a non-zero count is a real threat. This takes a bit longer, but forced spoilage or microbiological plating time-course experiments get us there.

Meanwhile, microscopy and DNA analysis provide us a fingerprint that we can use to track the organism through the facility, locate the origin and solve the root problem of microbial spoilage in beverages!

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