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Old 03-25-2011, 02:25 PM   #1
jpsloan
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Default Pervasive Acetaldehyde

I've developed an apparent system-wide issue with my beers. Acetaldehyde. This is a relatively new problem, so I'm trying my level best to ferret out how it's popping up in my beer. Here's the skinny...

Two beers in a row... both have that green apple jolly rancher smell and flavor, almost overwhelming when it reaches room temperature. The first is a doppelbock that was brewed in a group brew in early November. It followed what I consider a typical fermentation... six weeks on primary, two day diacetyl rest, then two months' lagering. The 20 gallon batch was split five ways, and we all pitched our own yeasts and brought them home to ferment. The wort was aerated with an aquarium pump and stone. The yeast starter was 1.5L for 4 gallons. Of note is that of the other four guys, none have developed any acetaldehyde character, which leads me to believe the issue had to have begun at the pitch or afterwards.

The next beer was a kolsch, brewed in February. 1L starter, three weeks on primary, then kegged and cold-conditioned for three more weeks before serving. This batch was not significantly aerated.

So, here's what these two beers have in common:
- both fermented in a white plastic ale pale bucket (without gasket)
- both yeasts prepared in a beaker with starter wort, similar sanitation practices, no stir plate used
- both were kegged in separate kegs, but my racking procedure was the same for both (autosiphoned into a cleaned and StarSan'd keg from elevated vessel)

From what I have read, there are four likely culprits for acetaldehyde... unhealthy yeast or underpitching, racking off the yeast too early, re-introduction of oxygen post-fermentation, and bacterial infection. I honestly don't feel that I'm pulling my beer off of the yeast too soon... it's the same fermentation periods that I've followed for four years, and this is the first time this particular off-flavor has popped up. I feel that it's possible that oxygen is creeping into the beer via the ale pales, but it's my understanding that it takes much longer for that to become apparent. O2 can be entering the beer as I rack from vessel to keg, but there is very little agitation, and no more contact with ambient air than any bottling/kegging procedure (I'm assuming).

This leaves me with unhealthy yeast, or contamination as the likely problems.

I wanted to get you guys' input, particularly if anyone has had this problem pop up and solved it... what did you do?


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Old 03-25-2011, 02:43 PM   #2
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For a while I had trouble with acet... but my issue resolved when I started kegging. Since you already are kegging, it appears I cannot offer much help. I am curious though, do you remember where you read that "re-introduction of oxygen post-fermentation" may cause acetaldehyde? That intrigues me a bit.

Good luck!


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Old 03-25-2011, 02:51 PM   #3
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Quote:
Originally Posted by -TH- View Post
For a while I had trouble with acet... but my issue resolved when I started kegging. Since you already are kegging, it appears I cannot offer much help. I am curious though, do you remember where you read that "re-introduction of oxygen post-fermentation" may cause acetaldehyde? That intrigues me a bit.

Good luck!
Acetaldehyde reduces to ethanol, and that is a reversible process.

Given that this happens with different yeasts, and it just starting happening and now happens for every beer, I would guess infection.
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Old 03-25-2011, 03:00 PM   #4
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Quote:
Originally Posted by -TH- View Post
I am curious though, do you remember where you read that "re-introduction of oxygen post-fermentation" may cause acetaldehyde? That intrigues me a bit.
From the Wiki, among other sources:

http://www.homebrewtalk.com/wiki/index.php/Acetaldehyde
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Old 03-25-2011, 03:03 PM   #5
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Quote:
Originally Posted by remilard View Post
Acetaldehyde reduces to ethanol, and that is a reversible process.
My first thought when I pondered the possibility that oxidization was behind this was "Wouldn't I also be getting lots of diacetyl?"

The other common element that didn't occur to me are the kegs. These are the second and third beers I've ever kegged. I feel really confident in my cleaning and sanitizing of the kegs, but I wonder if I don't need to replace my vinyl hoses and hammer my autosiphon with a good long Starsan bath?

Also, the guys in my brewclub seemed to feel that I should try fermenting in Better Bottle/Glass Carboy and see if that doesn't restrict O2, or possibly remove the contaminated plastic bucket.
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Old 03-25-2011, 03:17 PM   #6
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I would address the cheapest and easiest possible solution first-- the pale. If the pale has been used for many years its quite possible it has enough micro-scratches that it might be introducing infection. That being said this is only from what I have read. Best of luck. Keep us posted with your findings.
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Old 03-25-2011, 03:56 PM   #7
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Make that bucket a grain storage bin and replace it. They are not expensive and not worth creating another bad batch for. I think I pay about $15 for a bucket and lid.

Oxy your kegs and rinse out with starsan. Honestly, I doubt very much it's oxygen in the system.

Yeast problems are very easy to solve. Make them better. There's tons of info on pitching yeast, so it should be very easy to follow proper procedures and amounts.
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Old 03-30-2011, 01:32 PM   #8
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Thanks for the input, everyone. I've officially retired my plastic buckets. With any luck, this is just a bug I picked up in the plastic. I'll be rocking a weizenbock/dunkelweizen partigyle this weekend, so I sure do hope that blasting my after-cooling gear with my usual strident course of StarSan will keep things clean and green apple free!
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Old 03-30-2011, 01:37 PM   #9
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Sounds to me like a yeast issue. You would not be picking up enough O2 to notice, and you should be having other off-flavours if you have serious contamination. You mention a time schedule for your fermentation. What about SG readings? Just because it took 6+2 days to ferment the lager last year does not mean it will not take 8+2 days this time around. I always start the D-rest at 75% of expected attenuation. Yeast does not listen to fixed time frames.
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Old 03-30-2011, 02:05 PM   #10
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Are these your first 2 batches doing lagers/hybrids? What temp did you ferment at and how did you control?


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