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Canning Line Nightmares: What to Know About Megasphaera and Pectinatus
As brewers, we love our low DO levels and our cans of light, crisp lager in the summertime. Unfortunately, so do a couple of the stealthiest spoilage organisms known to the beer industry.
Besides exploding cans, I would say that this topic—a pair of the sneakiest, most pernicious bacteria that can be found in a brewery—has given me the most sleepless nights during my career of quality testing in the industry. The resurgence of light lagers and pilsners in the craft sector is pretty recent, so many of us, as craft brewers, may not even be aware of these especially harmful bacteria, which have usually only been a problem for macrobreweries.
Megasphaera and Pectinatus are two genera of gram-negative bacteria (think E. coli) that thrive in low-oxygen environments. Here, we’ll consider the detrimental effects of these bacteria, where they can be found in the brewing environment, and what can be done to prevent them from infecting your beer—so, hopefully, they don’t keep you up at night, too.
Besides exploding cans, I would say that this topic—a pair of the sneakiest, most pernicious bacteria that can be found in a brewery—has given me the most sleepless nights during my career of quality testing in the industry. The resurgence of light lagers and pilsners in the craft sector is pretty recent, so many of us, as craft brewers, may not even be aware of these especially harmful bacteria, which have usually only been a problem for macrobreweries.
Megasphaera and Pectinatus are two genera of gram-negative bacteria (think E. coli) that thrive in low-oxygen environments. Here, we’ll consider the detrimental effects of these bacteria, where they can be found in the brewing environment, and what can be done to prevent them from infecting your beer—so, hopefully, they don’t keep you up at night, too.
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Nasty Critters
Researchers often group these two bacteria together because of their similar growth environments and the off-flavors they produce. Both can grow in wort and in low-ABV beer, although Pectinatus can also grow in aerosols and in yeast pitches. The off-flavors they produce include extreme sulfur, rotten eggs, and butyric acid. Visually, samples with high infection rates also become very turbid.
They’re not only nasty; they’re also stubborn. Both types are hop-tolerant, and Pectinatus is acid-tolerant. So, those things that, as brewers, we usually rely on to help prevent bacterial infection—such as IBUs and reduced pH—are limited in their ability to kill off either of these.
They grow in low-oxygen environments and in light beer (below 5 percent ABV). Generally, breweries that package beer aim to minimize dissolved oxygen (DO) to maximize freshness and shelf life, but in this case that’s not enough—these bacteria can grow in beer with fewer than 0.3 milligram per liter of DO. Thus, the combination of minimal DO and low-ABV beer is like a perfect storm for their ability to tiptoe in, undiscovered, and then proliferate in the package.
So, they’re sneaky. See why they keep me up at night?
Once they inhabit a beer, they grow slowly over that beer’s shelf life. In the early days after a beer is packaged, Megasphaera and Pectinatus tend to be at very low levels that are difficult or impossible to detect. However, as the packaged product sits on the shelf and encounters warmer-than-ideal storage conditions, the bacteria grow over the next few weeks and months. Pectinatus likes temperatures around 68°F (20°C), while Megasphaera prefers closer to 82°F (28°C). If an infection occurs during the summer months and storage temperatures are not closely monitored, the chances of continued growth in the can or bottle are probable.
While it’s unlikely that a customer would be brave enough to drink a beer with this much sulfur present on the nose, consumption could result in sickness—especially if the individual has a sulfur intolerance or sensitivity. Safe practice is to remove any remaining product from the market if you believe that a batch is contaminated with Megasphaera or Pectinatus.
Environment and Detection
These bad boys are almost exclusively found in the nooks and crannies of packaging lines. Because these are the areas with the least amount of oxygen present, Megasphaera and Pectinatus can hide for many months without being detected.
In particular, the crevasses around the can seamer area are hot beds where these bacteria can thrive—and daily cleanings and even deep-cleans often overlook those areas. Plus, because Pectinatus can survive in aerosol environments, any spraying beer in this area can serve as a vehicle for infection into the can.
Testing for these two bacteria can be especially tricky, for the reasons mentioned above: Most breweries don’t realize that they have an issue until a particular batch is almost at the end of its shelf life. Megasphaera and Pectinatus are such slow growers that it can take months to show themselves in high enough concentrations to get a positive hit.
When you’re testing, the main issue to remember is that they are both oxygen-sensitive; all sampling must be done quickly, and testing needs to be done in tubes or CO2 chambers. Both Megasphaera and Pectinatus can grow in Hsu’s Lactobacillus and Pediococcus (HLP) medium when in anaerobic tube environments. Unlike with the conventional testing for Lactobacillus and Pediococcus in these tubes, Megasphaera and Pectinatus won’t show up as distinct colonies. When they are in high enough concentrations, they form a dense haze throughout the tube, except for a thin layer at the top where the most oxygen is present.
Prevention
Whether you’ve experienced a Megasphaera or Pectinatus infection or you’re just scared enough to never want to experience one, here are some tips on how to prevent these stealthy bugs from infecting your clean, light lagers.
Consistent testing of your DO readings is the first step in evaluating whether you’re at risk for infection. If you’re getting low levels of DO in your cans, it could be a good time to take a closer look at your cleaning practices in order to prevent this issue. Even if you aren’t taking DO readings, it is important to focus on regular cleanings of the seamer areas, especially in the summer. Consistent hot water and caustic rinses will help to prevent growth in these hard-to-reach areas. Adenosine triphosphate (ATP) swabbing can be a good way to double-check the cleanliness of these potential growth spots.
It’s also good practice to add extra micro-testing of your higher-risk (lower-ABV) beers over the course of their shelf lives. As mentioned above, HLP tubes can be a good first indicator of Megasphaera or Pectinatus beginning to take hold in a batch. If you suspect a potential for infection in one of your beers, begin by inoculating HLP tubes with beer from a warm, stored can every two weeks or so. That way, you’ll be able to document the growth in the packaged product visually from week to week.
Besides HLP tubes, there are more testing-kit options for polymerase chain reaction (PCR) verification. Or, you can send off a sample to an independent lab-testing service to get confirmation that this is the source of your infection.
Summer months, crispy lagers, and low DOs—all great things, normally—can nonetheless create chances for breweries of any size to encounter an infection of Megasphaera or Pectinatus. However, being aware of these bacteria and their potential to exhibit extreme off-flavors is the first step to being able to prevent it from tarnishing your beautifully clean beer. As for restful nights, however—no guarantees.
