Preventing Acetaldehyde

I don't think your fast and loose process points to an obvious answer but I have a few thoughts.

Pitching 1/3rd of the packet... Are you rehydrating your yeast? If not, it may be more like 1/6th of the packet, in effect. Or at least that is the dogma on dry yeast. For a 1 gallon batch, I'd think that would still be OK, depending on the OG. Anyhow, it points to pitching more or rehydrating as something to play with. Pitching more would be easier...

Temp control... Fluctuating temps may be a problem. Since your batch size is small, it may be more prone to ambient temp fluctuations (lower thermal mass). Maybe try to stabilize swings with swamp cooler approach, blankets for insulation, or similar.

No FG reading... yes, you are losing beer to the hydrometer, but until you figure things out, maybe you should be willing to sacrifice part of a bottle. Or brew a slightly bigger batch size to account for hydrometer readings. Maybe brew as though you were making 8 bottles. Get at least two stable readings a few days apart. More importantly, taste those stable hydrometer samples a few days a part. If the acetaldehyde is there, do not move beer yet.

 

I read frustration, Diacetyl is and the prominent flaw to worry about. So if that’s not occurring than it sounds like steps are being skipped in your process. What’s your process?(pitch)

 

Quoting Beer&Brewing Magazine:

“Brewers yeast produces acetaldehyde as an intermediate compound in the conversion of glucose to ethanol, so it’s found in every beer you make, at least during primary fermentation. However, in a healthy fermentation, the yeast fully converts the vast majority of this compound to alcohol so that any residual amount falls below the flavor threshold. If the fermentation is less than optimal, the conversion of acetaldehyde to alcohol may remain incomplete, and too much will remain in the final beer.

Acetaldehyde is also produced by the oxidation of ethanol (alcohol), such as may happen when exposing fermented homebrew to oxygen. It becomes even more problematic when aerobic bacteria get hold of it and metabolize this compound into acetic acid, which tastes of vinegar and is considered its own off flavor.”

Hope that helps. But pitching rate should be looked into. More or less proper fermentation should fix that problem.

 

Soap is the devil

 

How long after bottling before you crack one open?
Anything different with your priming solution (other than correctly scaling down) when compared with your 5-gallon batches?

 

Use oxyclean (fragrace free), PBW, or similar. I don't think that is the problem, unless you are using some sort of fragrant soap ("Dawn Green Apple? Why didn't I think of that?"). Still, you might need to start tweaking some variables.

My bottling approach is to fill with solution of oxyfree, scrub in and out a few times with bottle brush, dump, triple rinse with hot tap water, soak in star san for a few minutes, allow excess to drip drain for a little bit, not to dryness, then bottle.

I have never used carb tabs but maybe would try if doing 1 gallon. Not sure. It seems easy to add a sugar solution to a fermenter or bottle bucket, and I don't think you necessarily oxygenate your beer when doing so, at least to a degree that causes problems.

Good luck with getting to the bottom of your issue.

 

Even with all you’ve shared it still seems like throwing darts with one eye closed.

It’s interesting that you’re only getting “6 beers at best with one gallon”. Assuming you’re leaving the trub behind after the boil, that could make upwards of 40% head-space in your fermentor, which seems excessive.

Far as I know, and I’m ready to be corrected if wrong, preventing/mitigating acetaldehyde consists of (at the minimum) safeguards against: too much oxygen after fermentation, using too much refined sugar, infection, packaging or sampling too soon.

If I was in your predicament and there were no similar issues with my 5-gallon batches, I’d do an in depth written comparison of everything from boil to bottle, (especially on the cold side); age/quality of ingredients, water source/quality, cleaning/sanitizing solutions & methods, hands, brewing & bottling equipment & environment (fruit flies buzzing around?), scaling.....everything.

 

Soap used for cleaning or soap flavor? I would agree with both, if diacetyl was not detectable

 

- O2 after fermentation: Yes
- Too much refined sugar: I don't think so, but if anyone has info on that, I'm willing to learn. I suspect the supposed "cidery" character attributed (rightly or wrongly) to sugar could be confused with acetaldehyde, because of the apple association.
- Infection: I don't think so. At least I've never heard of any bugs with a propensity to make acetaldehyde (any more so than S .cerevisiae). But I'd love to see info to the contrary if it exists.
- Packaging too soon: Yes

 

From Yeast, White and Zainasheff, p. 96 and 97: Comparing 2 beers fermented with WLP001 @ 66*F and 75*F...
"The warmer fermentation shows a small increase in production of ethanol,fusel alchohols, and esters, but in sensory analysis, the beers tasted very different. The main flavor difference was a substantial increase in acetaldehyde, 10.5 times higher than the perception threshold."

Figure 4.16 shows 7.98ppm Acetaldehyde @ 66*F and 152.19ppm @ 75*F
(with 10ppm listed as taste threshold for Acetaldehyde)

 

When i do my 1 gal Jamaican ginger beer batches i just sanitize the hydrometer and float it in the bucket.No need to fill the test jar.

 

I think this is why you almost never see this problem (acetaldehyde) in veteran brewers (they are usually into temp control)...1 gal batches really do require more stringent temp controls, too.

 

Dang, didn’t leave myself enough outs, and batting .500 don't cut no ice in the brewhouse
Might have been better as “....preventing/mitigating acetaldehyde or cidery/vinegary flavors that could be considered similar depending on one’s palate, consists of......blah, blah”.
Then it would have been not only about acetaldehyde production but also about providing an environment conducive to producing palate subjective characteristics like those that are associated with acetaldehyde.

In similar twisted logic (not necessarily production of acetaldehyde but of like flavors, palate dependent), the below are cited in a lame attempt to CMA:
A BeerSmith Home Brewing Blog post suggests acetobacter in conjunction with post-fermentation oxygenation can provide vinegar flavors. (might be a stretch for some to equate vinegar with green apple)
FWIW wikipedia claims fruit flies are a common vector in propagating acetic acid bacteria, of which acetobacter is a genus.
One source suggested acetaldehyde is sometimes caused by bacteria due to poor sanitation procedures. I won't link it because I’m not convinced it’s accurate and, with extraordinary sleuthing, I deduced it's credibility was suspect after seeing it sells ladies pink t-shirts that say "I Brew The Beer I Fart".
The citations are anecdotal and don’t offer any evidence of being gleaned from formal, controlled studies.

Question:
For beer brewing, is the acetobacter that’s typically mentioned here aka acetobacter malorum?
If it is then this paper from UC Davis might be of interest where it states one of the physiological traits of acetobacter malorum is, "in low O2 produces acetaldehyde and ethyl acetate."