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?

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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...