The Beginner’s Guide to Diastaticus in Beer and How To Diagnose Gushing Bottles, Cans and Kegs

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This post is intended to give brewers without expensive lab equipment the tools they need to determine if they have a Diastaticus problem in their already packaged product.  If you’re reading this, chances are you already have “gushing” kegs, bottles and cans out in the market and need to know what’s up.

I’m an avid listener of the Master Brewers Association of America Podcast.  Recently, they did a two-part series on Diastaticus and how it relates to overcarbonation of beer kegs, bottles and cans.

It’s been a pretty hot topic of late and is even the subject of a law suit by Left Hand Brewing against White Labs.

I am a sponge for this type of info (OK I had a giddy schoolgirl moment – don’t be hatin’) but I realised if you’re a beginner, novice brewer or if you lack a very expensive lab at your brewery, diagnosing Diastaticus in your beer could be quite difficult!

MRW a new episode of the Master Brewer’s Podcast gets uploaded.

So, in beginner’s terms and for breweries on a limited budget, here’s my take on overcarbonated beer cans, bottles and kegs and how to diagnose a Diastaticus wild yeast contamination on the cheap.

I’m not going to help you in dealing with a Diastaticus infection in your brewery in this article – but at least you’ll have the info at hand to be able to identify and take steps to eliminate it in your brewery.

What’s Up With These Gushing Bottles, Cans and Kegs?

Have you ever been frustrated after working your butt off in your brewery, paying special attention to all of your QA and QC protocols and then sending your beer out into the world for it to become overcarbonated after a few weeks?

Why is it that your packaged beer which had finished fermenting in tank all of a sudden decided to referment in package?

You pitched the right amount of yeast, you even raised the fermentation temperature towards the end to assist in letting the yeast chew up all available fermentable sugars and diacetyl.

Heck – your beer hit terminal gravity and stayed there for some time before you crash chilled it!


So what gives?

Know Your Product


You make it but do you know what you make?

Yeah like duh.

In order to diagnose Diastaticus, you need to have identified your base beer specification.

One of the main things that you need to specify in any New Product Development (NPD) program is what the Target Finishing Gravity is and what the Target pH of your product is intended to be.

Specifying in advance what your carbonation level should be is also helpful.

Then, every time you brew this beer, you log a Bright Beer Analysis prior to packaging to ensure that each batch matches the product specification.

The Finishing or Terminal Gravity determines the amount of non-fermentable sugars in your finished product.  This is usually made up of dextrins.

The higher the Terminal Gravity, the higher the amount of unfermentable sugars in your beer.

These non-fermentable sugars make up the body of your beer.

Know Your Enemy – What is Diastaticus?

Diastaticus is a wild yeast infection in your product.

Wild yeast is simply yeast in your product that has not been introduced by you, the brewer.  It has come from outside of your brewing process.

Diastaticus is a Saccharomyces variant so it’s full name is Saccharomyces Cerevisiae var Diastaticus.

Diastaticus for short because frankly I’m short on time to say all that shit every time.

Diastaticus strains of yeast excrete an enzyme called glucoamylase outside of the cell wall.

Glucoamylase enzyme breaks down dextrins in your beer into fermentable sugars.  It can even break down starches.

Now that you have fermentable sugars in your product, your house strain of yeast, already in your product, is able to ferment those sugars.

Game over.

Too soon for a Bill Paxton meme? Nah….Rest in peace, Bill Paxton.

Here are some interesting facts about Diastaticus:

  • It looks like regular brewer’s yeast under a microscope.
  • It does it’s best damage at around 30°C/86°F – give or take a few degrees. Are you cold storing your product?
  • There is no known lower limit as to the number of cells in your product before it can do damage.  One cell is enough to cause gushing.
  • You can actually buy a Diastaticus strain and use it in your brewery/beer!   In this case, you don’t have a wild yeast problem – rather, your choice of house strain is the issue! Good times.

Commercially available Diastaticus strains are commonly known as Saison strains such as Lallemand Belle Saison which the manufacturer publishes in their spec sheet that it’s a Diastaticus variant (thank you for the transparancy and giving brewers the info, Lallemand!).

There are other commercially available Diastaticus strains.

You should check with your yeast supplier as to whether your strain is a Diastaticus variant.

Diagnosing Diastaticus Step 1 – Gather Bright Beer Information

Identify the batch code in the field that is displaying overcarbonation.

Go back and look at the bright beer analysis for that batch.

You’ll need to note the bright beer analysis of Gravity, pH, carbonation level and ABV at bright beer.

What’s that?  You didn’t take a detailed analysis each batch of your beer in bright tank prior to packaging?

MRW I see a brewer that doesn’t log bright beer analyses.

You can stop reading now because I can’t help you, sorry.

Diagnosing Diastaticus Step 2 – Analyse Your Overcarbonated Beer

OK – go grab some of your overcarbonated beer out from the field.

Take a measurement of Gravity, pH, carbonation level and ABV.

Be safe.  Bottles can explode.  Wear PPE.

Diagnosing Diastaticus Step 3 – Is it a Lactic Acid Bacteria Issue?

Compare the gravity, pH, carbonation level and ABV of your overcarbonated beer to your bright beer analysis.

Has the pH decreased in pack?

If yes – you may have a lactic acid bacteria infection.

Refer to a lab or plate up your product for lactic acid bacteria diagnosis.

Is the pH roughly the same?  Could be Diastaticus or it could be Brett.

One day I hope they name a strain of Brett after Bret Michaels of Poison.

Read on.

Diagnosing Diastaticus Step 4 – Is it a Brettanomyces Issue?

Perform a sensory analysis of your overcarbonated product.

Do you get any 4-Ethylphenol aka 4EP?  This is barnyard, horsey, band-aid or antiseptic aroma/flavour.

Do you get any 4-Ethylguaiacol aka 4EG?  This is bacon, smokey, clovey or spicey.

Do you get any Isovaleric Acid?  This is rancid/cheesy.

If you get any of the above characteristics then you may have a Brett problem.  Refer your beer to an outside lab for analysis.

For me, Brett smells and tastes like ketchup.

So much truth here.

If not, read on to determine if you have a Diastaticus issue.

Diagnosing Diastaticus Step 5 – Identifying Diastaticus Without a PCR

So you’ve gotten this far and you’ve determined that you don’t have a Lactic Acid Bacteria issue and you don’t have a Brettanomyces issue.


Let’s see if you have a Diastaticus issue.

If ALL of the following have occurred:

  1. Gravity has dropped compared to bright beer analysis.
  2. CO2 levels in pack have increased compared to bright beer analysis.
  3. pH has stayed relatively the same compared to bright beer analysis.
  4. ABV has increased compared to bright beer analysis.
  5. Sensory does not show any signs of Brettanomyces.

Then it’s likely you have a Diastaticus problem.

Is your head in the proverbial sand?

The best and fastest way to identify Diastaticus is to use PCR however, if you do not have access to a PCR unit, you can incubate a sample in Lin’s Cupric Sulfate Media (LCSM) media in an incubator at 30°C for at least 3 days and see if Diastaticus grows.

Normally LCSM media is used to detect non Saccharomyces organisms such as Brett but some strains of Diastaticus are known to grow on LCSM.

Take a look at the growth under a microscope to determine if it’s Brett (elongated cells) or Diastaticus (looks like regular brewer’s yeast).  Not overly conclusive but hey, it’s a good start.

Diagnosing Diastaticus Step 6 – Still Not Sure? Refer To An Outside Lab

No doubt, PCR is the best way to determine if you have a Diastaticus issue.

In Australia, there are some great outside labs such as Symbio Laboratories (formerly Food Laboratories) and Mérieux NutriSciences (formerly Siliker).

You should refer to a reputable food science lab in your local area.

Ask for a “qPCR” for Saccharomyces Cerevisiae var Diastaticus.

Lab crew do a great job so I keep my thoughts to myself.

Sure – you could have started here at Step 6 but hey, you would have missed out on all these spicy memes!


Gushing bottles, cans and kegs needn’t occur as often as I see it here in Australia.

And while cold storage helps contain the issue, this is one thing where us brewers can’t blame our warehouse and our customers for storing product poorly.  This is on us.

If you follow good QA and QC protocol, you’d be testing for Diastaticus during the production of your product. Be proactive.

It’s never a good idea to be testing for a micro issue retrospectively once a product has failed in the field.

The damage to your brand has already been done and you can’t put a price on that.

It is cheaper and better for your brand if you dump product prior to packaging.

Don’t be afraid to do that. Ever.

Cold store your product as well.  Though not a solution, it will slow down the effects of Diastaticus.

When cold storage of your product is saving your butt.

If you have read the above and you believe you have a diastaticus issue but are not sure how to deal with it….feel free to get in touch and I’ll give you some pointers.



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8 thoughts on “The Beginner’s Guide to Diastaticus in Beer and How To Diagnose Gushing Bottles, Cans and Kegs”

  1. another super simple low tech method for detection is to see if an isolate will ferment a 1-2% starch broth in a Durham tube. If there are is gas production, it’s likely bad news.

    I think it’s also possible to detect on on starch agar, where with large, clear halos around the colonies as they release amylolytic enzymes.

    1. Great point, Jon. I forgot to mention that Diastaticus can consume starches as well as dextrins so yeah, this would totally work. What’s the easiest way to make a starch broth? Or should one procure this from a scientific supplier?

      1. You can make them reasonably easily yourself – with just soluble starch (1-2%) with yeast extract and maybe peptone, making sure the starch is cooked to disrupt the starch grains. On mobile, so don’t have a reference on hand, sorry!

        1. Best in mind that most cheaper sources of starch will also contain Di- and monosaccharides, so you’ll likely see growth of non STA1 cerevisiae if it isn’t analytical quality starch.

  2. Thanks so much for that solid dose of learning in a very palatable form! You just clarified what’s {most probably} going on in my brewery. I’ll be checking out your other works.
    Cheers, Keith Ward {Home brewer in Taipei}

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