Diacetyl

[cliffo]

Hi All,

My last three AG lagers have ended up with Diacetyl (can't stand that taste/smell...yuck!!!).

This is from using three different strains of dry yeast - 34/70, S189 & S23.

I did a Diacetyl rest on all of these at around 1020 for 2 days but it still appears.

Can pitching the yeast at too warm a temp cause Diacetyl? Probably pitched the yeast around 20 degrees and let cool in the fridge to air temp of 10 (figure the wort would be around 12).

Anyway, I've managed to save two batches by warming up and pitching some older cooppers ale yeast I had in the fridge - far from ideal but 2 of the 3 are now drinkable so thats better than tipping them down the sink.

Cheers,
cliffo


EDIT - A few too many arvo beers before posting...well it is cricket season

 

[kevnlis]

Tipping them down the fridge :blink:

Pitch at recommended fermentation temp, pitch enough yeast for the gravity of wort ( http://www.mrmalty.com/calc/calc.html ), transfer to secondary with a CO2 purged fermentor, lager at least 2 weeks in secondary, etc.

 

[mika]

Pitching warm will increase diacetyl production. I would have personlly thought that 1020 was too high to start a rest. I'd be waiting till 1014. What temp was your rest conducted at ? Make sure when you do the rest that you do still have yeast activity though.
What was the terminal gravity of the beers ?

 

[Gulf Brewery]

Hi All,

My last three AG lagers have ended up with Diacetyl (can't stand that taste/smell...yuck!!!).

Hi Cliffo

I would wait until you are closer to FG before raising the temperature for the diacetyl rest. If you are aiming for about 1.010 to 1.012 then wait until the OG is around 1.015.

Did you have a good hard rolling boil? - I think it makes a lot of difference to lagers.

Diacetyl is commonly a yeast problem, so pitch warmer and get the yeast multiplying and drop the temperature to ferment temperrature before the yeast go anerobic, then raise at the end of ferment to remove diacetyl.


Cheers
Pedro

PS - you could always send me a sample for a 2nd opinion

 

[dr K]

Diacetyl is a natural part of beer but not a part that we want much of and in a lager any of.
You should do your diacetyl rest after you have reached your terminal gravity, essentially what you are doing is using the remaining yeast to mop up by-products. Diacetyl is not uncommon in some commercial micro beers where they have been rushed out. The other cause of diacetyl is open racking, you will introduce oxygen to the beer which will kick some of the yeast off, enough to a little ferment and a big diacetyl, this was certainly the problem I had about 6 years ago and was alerted to it (after all else failed) by a commercial brewer.

K

 

[dig]

During the synthesis of the amino acid valine, yeast produces the pre-cursor to diacetyl alpha-acetolactate that can find it's way into the beer. This converts in the beer to diacetyl which is subsequently taken back up by the yeast and broken down to a compound with a much higher sensory threshold than diac. Temperature at the end of ferment will speed the tranformation from acetolactate to diac and sustained yeast contact should then unsure that it's taken up.

Unless you have, say, a pediococus infection in which case so much diac will be produced, the yeast won't deal with it.

 

[mika]

Yeah...what he said.... :huh:

 

[cliffo]

Thanks guys. Next time I'll try doing the rest at a lower gravity and see if that makes a difference.

Thanks for the input.