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The removal and prevention of beer stone

Megan Gemmell beer stone kegs

This is an article I have been wanting to write for a while.

I, unfortunately, only learnt about beer stone the hard way.

The quality of beer coming out of my kegs was inconsistent from one keg to another. Some were perfect, while others kept developing off flavours and very high carbonation within a few weeks after kegging. It was a depressing amount of beer to be throwing away, and even more frustrating as I didn’t know what was going wrong. What I did know however, it was a sure sign that something was living in those kegs that shouldn’t have been. I thought it must have been something in my keg filling regime, but that didn’t explain why some kegs were fine, while others not. My keg cleaning always followed a strict hot alkaline cleaning protocol, followed by sanitising with Supersan (acetic acid based santiser) or Imperisan (phosphoric acid based sanitiser). I really thought I couldn’t be any more thorough. But I was still stumped.

On closer inspection, I realised that all my kegs that I had bought brand new, were not going off, while my second hand kegs were the ones developing these off flavours, even with their rigorous cleaning regime. When I removed the keg spears (which is not recommended), I soon realised what the problem was.

From the images below, you can see the build-up of a chalky grey-white scale on the spear threads. I knew this was the cause. It was beer stone...

Both the alkaline cleaners and acid sanitisers were not going to get into this thread enough to remove this build up, and even if they did, they would not remove this scale. This scale does not come off with a standard soak and scrub. I soaked the spears in a strong phosphoric acid/nitric acid solution (used in the dairy industry against milk stone) with intermittent scrubbing with a hard toothbrush, for weeks, and only then did it start to come off. This made it very clear to me that our simple cleaning practices are not sufficient to get rid of beer stone. When it comes to beer stone, prevention is better than treatment. It is worth the time and effort to avoid throwing, what was initially good beer, away.

What is beer stone?

It is a precipitate of calcium oxalate and protein. It can be found on the inside of your fermenters, as well as kegs, heat exchangers, aging tanks, beer dispense lines etc. Basically, everything that comes into contact with wort and beer.

How does it form?

Organic compounds (proteins and polypeptides) in wort and beer bind with the compounds found in the brewing water (calcium and magnesium) to form calcium oxalate, a white crystalline precipitate. Microorganisms can live and multiply in this precipitate, protected from standard cleaning processes.

It is also important to note that most breweries use caustic (NaOH) in their cleaning protocol, and unfortunately, this also contributes to beer stone formation (caustic reacts with carbon dioxide, usually in high concentrations in kegs and fermenters, to form a precipitate).

Effects of beer stone

Beer stone is not like the usual hard water scale that we see developing in our kettles and shower heads (largely calcium and magnesium based deposits). Beer stone also contains proteins which acts like a binding agent, which makes the scale much more hardy and therefore, more difficult to remove. This beer stone creates loads of places for microorganisms to “hide”, making it impossible to sanitise, so when your wort or beer is added to the vessel, it creates a perfect environment for the nasty critters to thrive. The effects might be minor changes in flavour profile, or major contamination issues, depending on the scale problem.

How do I remove beer stone?

Prevention is better than treatment. Once you can actually see the beer stone, you will have a very difficult time getting rid of it. You will need to use the chemicals used in cleaning at concentrations in their upper level of their recommended dose, and for a longer time.

Of course, you do need to approach an accredited chemical company for the recommended treatment of your vessels. This blog is merely a guide to create awareness of potential problems in your brewery. There are many chemicals on the market, most of which do not actually state what their active ingredients are, so rather do approach someone that is trained in this field. These chemicals can give off harmful by-products if mixed incorrectly.

As previously mentioned, caustic can actually cause the build-up of beer stone, so some breweries add sequestrants (chelating agents) such as EDTA to the caustic cleaners to prevent the precipitation of the calcium components, which ultimately form beer stone.

I have tried the following method suggested by More Beer, which is also commonly used by some breweries, and got great results (not without some serious scrubbing however). It uses a two-step approach: an alkaline cleaner to “digest” the protein, followed by an acid detergent to dissolve the minerals. Most cleaning regimes used to remove beer stone involve both an acid and alkaline (non-caustic) step.

Step 1: Rinse the vessel with ambient-temperature water.

Step 2: Use a phosphoric/nitric acid mixture as prescribed (maximum 60°C) for 15-30 minutes.

Step 3: Don’t rinse.

Step 4: Use a non-caustic alkaline cleaner as prescribed. CIP for 15-30 minutes, depending on conditions.

Step 5: Rinse with ambient-temperature water until the pH of the rinse water is the same pH as the tap water coming in.

If you are still not able to remove the beer stone, you may need to approach more hardy tactics. I find the dairy industry is full of options due to their similar problem with milk stone.

Of course, these chemicals are all hazardous, so again, I suggest you do speak to an accredited expert, as well as implementing all the safety measures.


Beer stone can creep up on you very suddenly. It may start off, initially, as some slight off flavours or aromas in your beer, not enough to say it was off, but enough to know that something in the processing may be going wrong. If left untreated, you will end up with a major problem, one which is difficult to get rid of, and you will have a lot of wasted beer in the process. Beer stone is NOT just something you MIGHT have to deal with when buying second hand equipment, no, it is something even your new equipment will eventually have if you do not follow good cleaning measures. When a pub is serving your beer on tap, and one keg is perfect, while the next is bad, who is at fault here? Of course, it is difficult to say, there are so many aspects to consider, but is it the barman for storing the keg wrong, etc etc, or maybe your keg was actually riddled with beer stone, and has now become infected? Definitely worth considering.


Removing & Preventing Beerstone Buildup. 2014. Accessed 11 July 2016. https://www.morebeer.com/articles/removing_preventing_beerstone. Originally Published by Steve Parkes - Brewing Techniques (Volume 6, Number 4).

Garrett Oliver. 2011. The Oxford Companion to Beer. Oxford University Press, USA, 09 Sept 2011.

Dana Johnson. 1998. Removing Beerstone: a look at alternative cleaning methods. Birko Brewery and Produce Specialist, Modern Brewery Age, March 23. (http://www.birkocorp.com/brewery/white-papers/removing-beerstone-a-look-at-alternative-cleaning-methods/). Accessed 11 July 2016


More about the Author, Megan Gemmell:

When I am not working as a microbiologist, I am brewing and studying beer. Being the geek scientist that I am, brewing yeast has become one of my main interests. After many years of brewing on my home-made system, squeezed into the laundry, I have taken the plunge and started Clockwork Brewhouse, and I’m loving it. 

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