When Draft Beer Goes Bad
Updated: Aug 28
In this first in our series on beer microbiology, we give you some background on what the problem is with microbe contamination in beer and where it comes from.
Background: What's the Problem?
Breweries work really hard to ensure the quality of their beer; they make sure all equipment is clean, they stick to rigorous hygiene standards and they carry out a battery of environmental and product testing. Every part of this is to ensure the beer that leaves their breweries is clean, clear of off-tastes and consistent with other batches.
Yet still, sometimes a punter at the bar will get the wrong impression; people wrinkle their noses at huge heads or flat beer and complain of a bad pint, an 'off' taste, a strange appearance or smell.
With such a variety of choice on the market, punters are quick to make decisions based on a first drink - if they get even one of these Bad Beers, they may never go back. For larger brands, this sullies their reputation as leaders in industry, and damages brand-loyalty. For smaller brands and craft beers, this is deadly serious.
The most unfair part? It's often not the breweries fault. So where do these off-tastes come from?
Supply Chain of Beer
To understand this, let's have an overview of how the beer has traveled:
Farm: hops/ grains harvested ->
Brewery: QA/ QC performed ->
If we've established that the issue with the beer comes post-brewery, a picture begins to emerge. Those familiar with the supply chain of beer will see where I'm going with this. The contamination usually won't come from the distributor - at this stage the kegs should be sealed.
The issue we see then is at the bar.
What Happens at the Bar?
At the bar, draft beer is served from a keg which has a line running up to the tap. Line-cleaning is the procedure where publicans and bars ensure the quality of beer they serve to customers. In it, the lines that run from keg to tap are disconnected; the lines are emptied, rinsed and cleaned; they’re dried and reconnected, and back to serving.
But sometimes this isn’t enough to get rid of the problem; yeast build-up, biofilms, or sources of contamination like mould near a keg. In other cases, the lines are being cleaned too often, but breweries and barkeepers have no choice but to err on the side of caution.
Because of this, bad beers can slip through the cracks. Beer lovers are vocal about their issues with other connoisseurs - one bad review can be enough to turn a whole social circle away from a certain beer for life - damaging the brand immeasurably. For craft brewers, a bad first impression is lethal.
So what it is at the bar that makes these once-good beers go bad?
Microbes in Beer
Potential sources of contamination include beer sitting in the lines too long, contamination from the tap, or contamination from the keg. These contaminants are often microbes.
Microbes like brewing yeast (Saccharomyces cerevisiae) are of course essential to the beer-making process, but contaminant microbes (both wild yeasts and bacteria) can infect the beer and the products of their metabolism can cause odd flavours.
Typically, these bacteria and wild yeast will not cause illness - common pathogenic bacteria like Staphylococcus aureus or Salmonella typhimurium will not survive in beer.
In our next post in this series, we'll explore some of the groups of microbes that can infect beer and cause it to go bad; affecting flavour, smell, appearance or acidity. Subscribe to our Twitter or LinkedIn to hear about our newest posts!
Cellix manufactures the Inish Mini-Bar, a portable device that can analyse beer straight from the tap with minimal preparation. See how it works here.