If you’ve ever experienced a butter or butterscotch flavour in your beer than you’re tasting diacetyl. The interesting thing about diacetyl, I think, is that not everyone can detect it as a flavour; of those who can detect it, some like it or don’t mind it, while others can’t stand it.
Diacetyl is a natural product of fermentation and is created and given off by the yeast cells early in fermentation. The yeast cells then take it back within themselves towards the end of fermentation and convert it into something almost tasteless – if a brewer stops the fermentation process before the yeast has finished its conversion, or if the fermentation stalls, then diacetyl will still be there (stopping it early could be the result of a need for brewing speed or just a slack move by the brewer; if it stalls early then the yeast is probably not healthy enough).
Lower temperatures towards the end of fermentation could see lazy yeast leaving behind diacetyl. One way to combat any leftover diacetyl is to include a diacetyl rest in the fermentation process, which involves slightly raising the temperature to poke the yeast into a final burst of action and leaving it for a further day. Diacetyl is an easy thing to prevent or control unless you’ve got a yeast infection.
An excess of diacetyl can be the result of a contaminated yeast which isn’t up to the job of converting the buttery flavour into a flavourless one, so the yeast needs to be fit and healthy. It could also be the result of an infection or bacteria in the yeast or the presence of wild yeast – some of these produce diacetyl. However, some strains of yeast just throw off more diacetyl that others when they ferment (pale ale and lager yeasts often do).
Beer shouldn’t taste like butter but small amounts are appropriate to some beer styles – pale lagers and some pale ales. In larger volumes diacetyl can give a fatty, slick mouthfeel (as if there is some melted butter in your pint...) which is very unpleasant. If your pint tastes like butter then you might not want to finish it, but that’s down to individual tastes and it’s not a fault that will do you any harm.
Diacetyl is one of the off-flavours which many find easy to recognise and can sniff it out an arm’s length away. I used to enjoy the flavour in beer (mmm, this has a delicious buttery taste!) until I realised that it shouldn’t be there and now my inner beer geek just screams out DIACETYL! whenever I taste it. I now only get on with it if it’s in small volumes. Are you sensitive to diacetyl? Do you like it, tolerate it or hate it?
This is the first in a series of posts looking at when beer goes bad. Being neither a brewer nor a scientist I’ve tried to keep it simple and from a drinker’s point of view. If I’ve missed anything interesting or important out then please add it below.
I used Beer Sensory Science (a great blog!) to help with this post.
Yes. Can't stand the stuff.ReplyDelete
I can recognise it but don't particularly mind it. And surely Caledonian beers are knowingly brewed with a hint of diacetyl on the palate.ReplyDelete
I find Diacetyl the easiest of the off flavours to pick out and the one I feel most confident about giving a name. But that's only after someone had pointed it out to me and said 'what you're tasting is diacetyl'.ReplyDelete
Great post, Mark. Think you've pitched it just right. Looking forward to the rest of the series.
Mudgie - I know Deuchars is a prime example of diacetyl in beer. For it to always be there it makes you think that they intend for it to be there. I used to love Deuchars for that taste as well but I haven't had a pint for ages.ReplyDelete
Chris - Glad you think it's pitched right. It's taken a lot of tweaks and flicking through books, plus emails to Mark at Beer.Birra.Bier for help, to get it here!
Diacetyl is the off-flavour I feel most confident about as well, mainly because it's unique and pervasive on the palate (for me, anyway). I'd be interested to hear from someone who can't detect it...
I'm quite fond of it, though I found an early diacetyl flavoured lager from Brewdog dire.ReplyDelete
You could compare this with mouse in cider which some people can detect and some can't. And which, yes, does make the cider taste oddly furry :-(ReplyDelete
Diacetyl always tastes more of plastic than butterscotch to me. Horrible.ReplyDelete
Assuming I'm tasting the right thing, then I prefer a bit of a buttery taste to a beer.ReplyDelete
Whilst warmer temperatures encourage Diacetyl reduction, the particular yeast strain used in the beer can have an effect. A highly flocculent yeast strain will be less suited to reducing the perceptible levels of diacetyl than a less flocculant one.ReplyDelete
Another method of reducing the levels of diacetyl as well as performing a rest is krausening the beer with freshly fermenting wort which will have healthier yeast to mop up the last of the diacetyl
I'm not sure defining a flavour as "off" when you admit that some enjoy it and can certainly be there deliberately is helpful.ReplyDelete
If intentional, then it's good. If not, then it's bad.
I find it hard to respect any opinion that changes just because conventional wisdom says it's wrong.
Mudgie - Mouse is a new one to me!ReplyDelete
Neil - Thanks for that extra info!
Pete - Diacetyl is a natural product in all beers but if there's too much then it's an off-flavour. Alcohol is the same: present in all beers but if it tastes fusel and hot then it's not right. If some people like the flavour then it won't do any harm to them but it's good to know when it should or shouldn't be there. I didn't mind the flavour when I first tried it, and like it in some lagers, but knowing that it shouldn't be in certain beers is not enjoyable.
Same issues occur in winemaking. The plastic smell is a different issue. Many refer to the smell as new band aids. This is another volitile acidity issue completely. Most of these problems arise when sanitation practices are overlooked.ReplyDelete
The beer snob won on this one. Interesting your inner geek told your taste buds not to like something. On one hand I am glad to see the recognition of bad beer, but on the other hand if you like bad beer there is nothing wrong with liking it. You are who you are.ReplyDelete
Great to see you doing these posts, Mark. I shall look forward to the one on "sunkissed" beer with particular interest!ReplyDelete
I was recently in a local brewpub where the Barman was actively selling his beer as "Popcorn" flavoured!ReplyDelete
Great post Mark, I'm really keen to learn as much as I can so I can confidently speak about these beery faults and intricacies, look forward to reading more.ReplyDelete
I can't say I've ever knowingly picked this taste out, but then wasn't really looking for it. Are there any beers out there that always have this trait so as to test the taste-buds for future reference?
Like most off flavours, the heavier the beer the more you can get away with. Some of your american light lager brewers are so shit scared of diacetyl, they track it through the maturation, targeting <7ppb. Normal human threshold is around 100ppb. Liking the scientific approach to tasting, how about some positive flavours too?ReplyDelete
Small Time Drinker - Unfortunately if I taste diacetyl then my inner geek just makes it the most dominant flavour in the beer and it ruins it. But then if it shouldn't be there then it shouldn't be there. It's kind of like having a lasagne made with star anise in it - it might taste ok until you work out what the flavour is and then it's just weird and overbearing and you wish it wasn't there!ReplyDelete
Des - 'Sunkissed' is coming soon and it's the most effusive!
Jonathan - That's brilliant!
Phil - Deuchars IPA is one that always has it in. Otherwise try lagers - I'm not sure of a major name that has a detectable level but I'm sure there are (I had a PU at the weekend and tasted it in that).
Bumpby - Interesting! <7ppb is very low. I wonder why some of the big ones do make it that low and others don't? As for positive flavours... any suggestions?
Positive flavours. Off the top of my head. Green apples, kettle hop, roses, grass, liquorice, phenol, cloves, bananas in wheat beer. Although like all flavours, excess is a bad thing and what is good for one style is not necessarily good for another. That also applies to the modern fetishisation of overly hopped beer. Can't wait for the lightstruck post, I've got some thoughts.ReplyDelete
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Diacetyl can be summed up in three words—Old. Speckled. Hen.ReplyDelete
Love it or hate it, diacetyl has become that beer's signature "flavor." Personally, the texture of OSH off nitrogen bothers me more than the butterscotch-iness.
Bumpby - I've got a few of them coming up but under off flavours - apples and phenols. I'll look into the others - I'd like to do estery flavours, wort and metallic but I need to do more research, although these are all 'offs'. Lightstruck is coming later this week.ReplyDelete
Craig - OSH isn't a great beer, especially off nitro! Stick to the US stuff you can get!
Yeah, no kidding. It's a shame that a lot of American's think OSH is great and indicative of all UK beer.ReplyDelete
Suddenly it all makes sense... one particular round of drinks a couple of years ago in Estonia will always be remembered as "the pints of butter".ReplyDelete
It was a local lager that was fine everywhere else. I never understood what the taste was (until now), but all 6 drinkers agreed that it was awful!
Andy - Delicious butter beer!ReplyDelete
Deuchars is famous for having it, but it's not ALWAYS there. I've been to the brewery several times and it was never present in the beers at the brewery tap.ReplyDelete
I've generally tended to think all Caledonian beers have a hint of diacetyl - in a sense it is their trademark. I've recently had a couple of bottles of 80/-, which clearly has it, but is still a superb classic beer.ReplyDelete
You know what - I don't actually mind it in small doses. Oxidisation - now there's a bad one, for me!ReplyDelete
Deuchars is a beer I've never liked so perhaps the diacetyl is teh cause, I'll have to try it again and see if I can detect it.ReplyDelete
Assuming I'm tasting the right thing, then I prefer a bit of a buttery taste to a beer.ReplyDelete