Removing diacetyl

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Removing diacetyl

Postby jeffjm » Sun Mar 31, 2013 4:43 pm

I've got a bock that has a very unpleasant diacetyl character. A while back there was some discussion about removing diacetyl by pitching a small amount of actively fermenting beer, more or less a starter, into the larger batch. What are the specifics of this process? Can I use any yeast strain, like the nottingham I keep in the fridge for emergencies? How much fermenting beer do I need, and how much yeast should I use? Does it make a difference if my beer is already carbed?
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Re: Removing diacetyl

Postby beermikester » Mon Apr 01, 2013 9:10 am

I've had pretty good success de-diacetyl-izing beer. What I've done may or may not be 100% needed, but like I said, it's worked for me.

1) De-carbonate your beer. You obviously want to be careful that no bugs can get into your keg while the valve is open. I keep a clean cloth that is soaked in StarSan draped over the keg valve. Make sure the cloth stays wet with StarSan.

2) Make a starter. I've always used the same style of yeast that I made the beer with. It may or may not be necessary to use the same strain, but like I said, it's worked for me in the past.

3) Bring the keg up to room temperature.

4) Pitch the yeast from the starter when it is at high kreusen. This is important. Others can chime on on the exact chemical reason for this, but when the yeast is at high kreusen, it is nice and hungry and gobbling everything up. Add it to the beer at this time and it will eat up the diacetyl.

5) Taste it after a couple days. If the diacetyl has been removed, you may want to rack it into another keg to leave behind some of the newly formed trub.

On Tap: Northern Brown Ale, Imperial Oktoberfest, Saison, Kolsch
Fermenting: Saison, IPA
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Re: Removing diacetyl

Postby siwelwerd » Mon Apr 01, 2013 6:07 pm

Did you taste it before racking it?

beermikester wrote:2) Make a starter. I've always used the same style of yeast that I made the beer with. It may or may not be necessary to use the same strain, but like I said, it's worked for me in the past.


I'd think something like US-05 would be best at cleaning up the diacetyl without producing any more of it. A lager yeast would be a good choice if you want the yeast to keep working after you cool it back down; but I'd lean more toward keeping it warm until the diacetyl is all gone.

4) Pitch the yeast from the starter when it is at high kreusen. This is important. Others can chime on on the exact chemical reason for this, but when the yeast is at high kreusen, it is nice and hungry and gobbling everything up.


Yeast produce diacetyl through the end of the exponential growth phase, and then enzymatically reduce it during the stationary ("conditioning") phase. There's a nice chart of diacetyl levels on p. 112 of the White/Zainasheff book. It's not so much that the yeast is "hungry", it's more about the yeast starting with the easiest sources of energy first (sugar), and then moving on to enzymatically reducing things like diacetyl and acetaldehyde. You want to catch them as they are shifting from sugars to cleaning things up, and before they have decided there is nothing left and gone dormant--high krausen is the best visual indicator that they are in the exponential growth phase, and will soon switch to the stationary phase.

Fun side note: apparently there is a product called Maturex that enzymatically reduces the diacetyl precursor alpha acetolactic acid. As you might expect, Google is case insensitive and MatureX is something entirely different.

P.S. Mike, did this work on that Bock you had brought to the BJCP exam?
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Re: Removing diacetyl

Postby tlael » Mon Apr 01, 2013 6:50 pm

siwelwerd wrote:P.S. Mike, did this work on that Bock you had brought to the BJCP exam?

zing! my daughter (7) still talks about that "popcorn beer" :D
siwelwerd wrote:Google is case insensitive and MatureX is something entirely different.

and LOL, I found out a second too late, but bookmarked several lovely sites.
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Re: Removing diacetyl

Postby beermikester » Tue Apr 02, 2013 6:47 am

siwelwerd wrote:P.S. Mike, did this work on that Bock you had brought to the BJCP exam?


Believe it or not, it did actually clear up a lot of the diacetyl before I brought it to the meeting. I think next time, I would use the SO-5 like Drew suggested to see if that cleans it up better.

Mike

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Re: Removing diacetyl

Postby jeffjm » Tue Apr 02, 2013 5:09 pm

I may have sabotaged myself to some extent. Last weekend, and again on Sunday, the beer had a massive diacetyl taste that was pretty disgusting. But last night, it tasted much better. It's not perfect by any means, but also not like drinking spray "butter". Today I realized that on Sunday, I'd eaten a couple of sweet Hawaiian rolls not too long before sampling. I ate another roll just now, poured a sample, and the taste was off again. I don't know what I would have eaten the prior weekend to produce the same effect - maybe crackers.

And yes, I tasted the hydrometer sample before kegging, and I don't recall there being any major problems beyond needing some lagering. Presumably I didn't eat anything buttery prior to tasting.
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