Like most brewery microbes, enteric bacteria are likely hiding in your cellar at this very moment. But with so many beer-spoiling organisms active in the brewing environment, why should we put this one near the top of our concern list?
I’ve said it before and I’ll say it again: As brewers, we’re very lucky to be working with a product that makes life inhospitable for microbes. However, there are still quite a few bugs that can manage to survive in beer and wreak havoc on your product’s quality and consistency.
You’ve probably heard about enteric bacteria in relation to gut bacteria—in fact, enteric literally means “related to the intestines.” And as long as they’re in our intestines, Enterobacter are necessary and beneficial. It’s once they leave that area that the real issues arise.
It’s important to understand the potential for infection, how we can test for the presence of these bacteria, and what we can do to prevent them from sticking around in our products.
Spoiler Alert
Enteric bacteria can cause problems for both wort and fermentation.
The wort-spoilage aspect means that the bacterium can have aroma and flavor impacts before the beer even hits the fermentor. These impacts usually show up as DMS and other sulfur notes. There can also be some vegetal aromas, including parsnip-like notes. In the cellar, meanwhile, enteric bacteria can cause fermentations to stall.
Notably, the wort and fermentation versions—because they’re in contact with different environments—act very differently. That can help you to identify the source and which version might be present.
The enteric bacteria that spoil wort are ethanol sensitive. While they can still impact flavors and aromas well into fermentation, they are not likely to survive long in that environment.
The enteric bacteria that affect fermentation, however, are the hardier of the two versions. These variants are alcohol-tolerant—in some cases up to 11 percent ABV. They’re also hop-tolerant, so they can show up in almost any style. Just to make things worse, the enteric bacteria that affect fermentation also can contaminate yeast, thus they can transfer into subsequent batches through repitching.
One of the most troublesome characteristics of enteric bacteria is their ability to create a biofilm. This is where proteins in the bacteria join together to create a sort of mesh. If not eradicated through cleaning, that layer will continue to grow upon itself with each subsequent growth cycle—to the point where it’s almost impossible to remove the biofilm if it’s not addressed properly.
Put It to the Test
The only way to get a real sense of the type and quantity of enteric bacteria in your brew is through microbiological testing.
There’s a lot that goes into setting up a micro program for your brewery. (See “Starting Up, and Sizing Up, Your Brewery’s Own Lab,” brewingindustryguide.com.) Here, I’ll just touch on the media and testing points when it comes to this particular bug.
The media type that best detects wort and beer spoilers such as enteric bacteria is LMDA+, which stands for Lee’s Multi-Differential Agar plus Cycloheximide. Let’s break down what those words mean:
- Lee is brewing scientist S.Y. Lee, who developed this media with his colleagues at Coors in the 1970s.
- Multi-Differential: You can differentiate among colonies that grow on this media type based on their specific biochemical processes.
- Agar is a gel that contains nutrients and provides a surface on which the bacteria can grow.
- Cycloheximide is an addition to the LMDA media base that inhibits protein synthesis in yeast. That way, we can conclude that any growth we see on the petri dish is due to bacteria alone.
LMDA+ is my medium of choice for detecting enteric bacteria because when growth occurs on these petri dishes, they’ll usually be visually very distinct. The morphology is unlike anything you usually see from brewing microbes. The colonies tend to have irregular edges and expand quickly. They also grow vertically upon themselves, looking like mountain peaks.
When in doubt, you can also do a gram stain. Enteric bacteria will be gram-negative, catalase-positive and have a rod morphology when viewed under the microscope.
An Ounce of Prevention
A huge part of preventing enteric infections is knowing where they like to hang out in our breweries.
Enteric bacteria are generally happy to reside in raw materials and bodies of water. That can include any source of water in the brewery, but it especially applies to standing water on floors. There tends to be an uptick in enteric bacterial infections in breweries during the summer, as the bacteria are happy to revel in the environment’s heat and humidity.
Now we get to the most important point: How can you prevent enteric bacteria from entering your beers. I’ll start by telling you something you already know: Clean, clean, clean.
The first time I encountered this bacterium in a brewery, I went around swabbing different surfaces of the tank farm. My sample points included the wet floors, sides of fermentors, and buckets of sanitizer that had been sitting out for too long. All these sources proved to be full of enteric bacteria.
The bacteria had been infecting a 24-barrel fermentor, and I was able to at least narrow down the source of the infection. It might well have been a hose that was dropped on a wet floor and not re-sterilized before it was connected to a tank. Another possibility is that a brewer was wearing gloves but not changing them out frequently enough when assembling the tank; that would lead to the transfer from infected surfaces to clean surfaces on the fermentor.
Cleanup
If you suspect or confirm that you’ve had an enteric contamination in one of your beers, you’ll want to clean that tank properly to prevent the biofilm from sticking around. That means implementing an infection-cleaning protocol of hotter chemical temperatures and increased contact times.
Ultimately, it’s always a good idea to reevaluate cleaning practices—especially before going into the hot and humid months. Also, it’s important to make sure all personnel are on the same page with proper procedures when they drop a part or gasket; they should also be frequently changing gloves and remaking sanitizer buckets.
Those are the kinds of careful practices that can prevent this bacterium from impacting multiple batches of your beer.