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When Draft Beer Goes Bad

Updated: Aug 28, 2020


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.

Image of a Brewery

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:

  1. Farm: hops/ grains harvested ->

  2. Brewery: QA/ QC performed ->

  3. Distributor ->

  4. Bar ->

  5. Patron.​

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.

Cellix Draft Beer being Poured

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