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Had a bottle of Nogne O porter a while back and was comparing it to my own porter and Fuller's London porter. The Nogne O was pricey but I thought it would be worth it as it was a bit special. Jaysus, when I drank it, it tasted heavily, really heavily of butter - I'm guessing this is diaceytl. Was really disappointed and found it hard to finish - which is rare for me. Is this supposed to be a characterisitic of this beer? I'm thinking not. Now that I got the taste of it, I have detected it in my own beer (very low levels in the porter, not in all bottles) which is a bit off putting as I hadn't noticed it before. What's the easiest way of knocking diacetyl on the head? What's the best thing to do to prevent it/limit it in a brew? For the record the Fuller's went down really well!

Dara

"Dara":2fpyws1v wrote: Had a bottle of Nogne O porter a while back and was comparing it to my own porter and Fuller's London porter. The Nogne O was pricey but I thought it would be worth it as it was a bit special. Jaysus, when I drank it, it tasted heavily, really heavily of butter - I'm guessing this is diaceytl. Was really disappointed and found it hard to finish - which is rare for me. Is this supposed to be a characterisitic of this beer? I'm thinking not. Now that I got the taste of it, I have detected it in my own beer (very low levels in the porter, not in all bottles) which is a bit off putting as I hadn't noticed it before. What's the easiest way of knocking diacetyl on the head? What's the best thing to do to prevent it/limit it in a brew? For the record the Fuller's went down really well!

Dara[/quote:2fpyws1v]


The choice of yeast strain and the correct pitching amount would be the first stop.

Here's what Palmer has to say:

"Diacetyl
Diacetyl is most often described as a butter or butterscotch flavor. Smell an unpopped bag of butter flavor microwave popcorn for a good example. It is desired to a degree in many ales, but in some styles (mainly lagers) and circumstances it is unwanted and may even take on rancid overtones. Diacetyl can be the result of the normal fermentation process or the result of a bacterial infection. Diacetyl is produced early in the fermentation cycle by the yeast and is gradually reassimilated towards the end of the fermentation. A brew that experiences a long lag time due to weak yeast or insufficient aeration will produce a lot of diacetyl before the main fermentation begins. In this case there is often more diacetyl than the yeast can consume at the end of fermentation and it can dominate the flavor of the beer."
<!-- m --><a class="postlink" href="www.howtobrew.com/section4/chapter21-2.html">www.howtobrew.com/section4/chapter21-2.html

. Diacetyl to me tasted far more like butterscotch candy than real butter (exactly like Worthers Original if you've had them).

It's generally a sign of rushed fermentation or infection. If a fermenting beer is cold crashed (home brew technique) or filtered right after primary fermentation has finished (when co2 bubbles stop evolving) the yeast will not have time to cleanup and remove diacetyl which is an early fermentation by product. Too much diaceryl may be produced if yeast is pitched too hot, too and then there's simply too much diacetyl to cleanup. Certain strains may produce above average vicinal diaketones, which are the precursor chemicals to diacetyl; some may also simply flocculate too soon; before all the diacetyl has been reduced

Most medium and small craft breweries test their VDK levels and just don't let fermentation finish until diacetyl precursors have been reduced.

Personally I like diacetyl in malty beers. I would be so sad if diacetyl was eliminated from all beers.


U can check for diacetyl in your home few by found a diacetyl force test; search the beoir forums for my thread on the subject.

Adam

Very apt comment at the moment Adam. You must have being reading my mind. I am currently putting together a wiki article on this for the wiki section here[/url:bg1f3242]. I was only just reading that old discussion thread about it and reading also the recent BYO magasine article.