Wednesday, 22 June 2011

When beer goes bad: Autolysis

Have you ever had a beer which tastes like marmite, burnt rubber or soy sauce? If so, what you are tasting is yeast cells which have died, ruptured and spilled their beer-spoiling guts into your brew...

Autolysis will be most common in old beers and I’ve had it often in aged bottled-conditioned strong ales but it’s also possible in fresh beer, where it will produce a burnt rubber aroma and taste. As a flavour I don’t mind it in strong, dark beers, finding that it adds a depth of complexity to the beer if it’s not too overpowering, but given its umami, marmite-like flavour (marmite being yeast extract), I’m guessing it’s a love-hate thing with other people.

What causes autolysis? Firstly, unhealthy yeast cells are more prone to it than healthy ones because they are weaker. It’s also due to stresses put on the yeast during fermentation. It can be caused by too-rapid warming or cooling of the beer during fermentation; a fermentation temperature which is too warm; exposure to high temperatures after fermentation (keep that bottled beer somewhere cool!); the hard work of trying to ferment a strong beer can leave the yeast cells dying in the beer; and strong bottle-conditioned beers rely upon the secondary fermentation to keep them going and if the yeast inside gives up then autolysis comes along.

I asked Mark from Beer. Birra. Bier. to look over these posts (because he homebrews and knows lots of stuff about beer) and he adds the following about autolysis: “A big thing here is oxygen. If oxygen isn’t present when the yeast cells are multiplying then the cell walls of the yeast cells that result will suck. Leaving beer on yeast cells for long periods of time will also cause autolysis and crappy unhealthy yeast cells are just more likely to want to explode and die.” (I love the last line and have visions of crazy, lazy kamikaze yeast cells self-destructing because they’ve had enough!)

This piece by Moritz Kallmeyer is very informative. Interestingly, as well as imparting those flavours to beer, the autolysed yeast cells also release “proteolytic enzymes which degrade beer-foam proteins and also increase protein and carbohydrate hazes,” it releases lipids (fats) and will increase the pH value, affecting the perceived flavour. None of these are good things.

Autolysed beer is generally not good because essentially a major part of it has died. Have you tasted beers which have these flavours? Is it something you like or dislike in a beer? Have you ever had a fresh beer with these characteristics?


This is another flavour which won’t do you any harm and which can add an interesting complexity to strong, dark beers, although it can kill fresh beers and leave them undrinkable. As with all the off-characteristics it’s down to the perceptible level and individual taste. Autolysis is also something which I knew nothing about until a few months ago; I’d tasted it but had no idea where that marmite flavour came from (glutamic acid is a breakdown product of the yeast). If anyone has anything to add to the science stuff which I may have missed out then please do.

And this is a question which I could use some help with (because I'm writing these posts so that I can learn stuff): In very hoppy beers, often ones around 7-8% which aren’t exactly fresh but also aren’t old (let’s say 5-8 months old), I’ve tasted rubber bands and assumed it’s come from tangy, intense old hops. Is this autolysis or is it from the hops? My instinct, because it doesn’t taste great, it towards autolysis...


  1. Too long on the yeast. Yep. Autolysis. One of the best internet sources for this kind of stuff tends to be in homebrewing groups etc. They know all kinds off shit, which I assume they have read elsewhere and condensed.

    I just checked Charlie Bamforth's book, the Art and Science of Brewing. It doesn't get a mention, though I dare say it does in others he has written.

  2. Hallo, this is an interesting post. But I am a little confused, since in my country (Greece), marmite as a food product is rather unknown (I've never tasted it).
    But after reading this, I wonder is it really healthy? I mean does it contain "damaged" or "dead" yeast cells?

    I have eaten food cooked with soy sauce, so I know how it tastes like, but I don't remember having ever tasted its flavour in a beer.
    Anyway, I guess I'll pay more attention to beer smells from now on.

  3. I get a burnt rubber taste from light struck beers.

  4. Tandleman - The homebrew forums can be really interesting. Sometimes takes a bit of trawling to get through though! Odd that it doesn't get a mention in Bamforth's book. I used Randy Mosher's book to help with this but that is only basic info.

    The Dark Chef - Just think of an umami savoury flavour like rich beef stock. There's nothing unhealthy about autolysed beer (as far as I know) it just means the yeast cells are no longer doing their job or haven't been able to properly do their job before spoiling the beer.

  5. I got a massive burnt rubber flavour in Kernel's Export India Porter, and am now wondering if it was meant to be in there? It was certainly a super tasting beer. If I missed it in the post I apologise but can brewers produce this off-flavour as a means to flavour a darker beer?

  6. The marmity flavour was something that was really noticeable when I tried some of the Bass Kings Ale I opened at my works party a few weeks back, but rather than bringing a harsh flavour to the beer, it really cut through the other flavours and brought a really nice depth of character to it. I also tried a bottle of Thomas Hardy Ale a few weeks before that and found the same “umami” flavour, but being a younger beer, it wasn’t as layered as the Kings Ale. Read about it here.

  7. Ghost - I don't think it's something a brewer would want to produce deliberately. I guess you could get a richer, roastier flavour depending on the dark malts used though?

    Matthew - Yep, I've had ales like that which have been very strong in flavour - some have been good and others undrinkable (one was just like soy sauce and horrible!)

  8. Ghost - interesting point about the Export India Porter. It's the only Kernel beer that I haven't enjoyed.

    I got a heavy burnt flavour, which wasn't a bad thing, but it was unbelievably fizzy for a dark beer (far too much so for me). It was like opening a shaken-up bottle of Coke.

    I'm not sure if this amount of fizz is intentional, or if something had gone 'wrong' in that particular bottle.

    Everything else I've had from Kernel has been superb.

  9. Well must say, this article was very informative. Quite a few of our friends who are hard-core beer drinkers believe that the stronger the taste of the beer, the better it is. It may be a valid point but there is a line of difference between the beer being strong and being physically repulsive to the taste buds! This post was quite an eye-opener, folks.

  10. The last time I opened one of my precious bottles of 1993 Courage Russian Stout that unami/gravy/Marmite flavour really stuck out but in a beer like that I treat it as a taste characteristic of ageing.

    "Burnt rubber" to me is something different. I've usually identified it with crystal malt but it tends to be there in a good few microbrewed bottle conditioned British amber ales, so maybe it is an off flavour from autolysis. It often seems to be underlined by acidic tastes from beers that haven't been bottled hygienically enough.

  11. Claudia - There is something to be said for the wonderful subtlety of some beers! It doesn't need to punch you in the face to taste nice!

    Des - Interesting. The burnt rubber taste is something I've had before but admit that I don't know exactly where it comes from... I'm putting 2 + 2 together with that one.

  12. something in the back of my mind is saying burnt rubber can be caused by insufficiently malted barley or poor quality barley being malted, can't think of where that "fact" got into my head from.

    I had a marmitey beer at cheddar beer festival last weekened, will look at my notes when I get home to find out which one. I love marmite and umami is a good thing in thicker bodied beer, wouldn't want the salt in it though!

  13. Des said: "It [burnt rubber flavour] often seems to be underlined by acidic tastes from beers that haven't been bottled hygienically enough."

    Yeah, I think that's an important point. In fresh beer I'd guess that the burnt rubber flavour is more likely to come from phenols. Possibly from an infection during brewing or bottling (as Des suggests) or through a fermentation that was too warm. I wouldnt think that many breweries have the luxury of being able to leave beer on yeast for too long in primary - tank space being at a premium and all that.

    Just catching up with these posts - good work, liking them a lot.

  14. Autolysis has always been something that I have disliked in certain champagnes so I wasn't particularly taken by the Weihenstephaner/Samuel Adams co-pro Infinium which, to my palate at least, is full of it. For us Australians it's a Vegemite flavour and that's not really something I like in an expensive bottle of anything.