Chronic off-Flavour in BIAB

“m) acetaldehyde

This compound has the taste and aroma of fresh-cut green apples, and has also been compared to grass, green leaves and latex paint. It is normally reduced to ethanol by yeast during the secondary fermentation, but oxidation of the finished beer may reverse this process, converting ethanol to acetaldehyde. Elevated levels are generally present in green beer or if the beer is prematurely removed from the yeast. It can also be a product of bacterial spoilage by Zymomonas or Acetobacter…”

http://www.bjcp.org/course/Class5Lesson1Troubleshooting.php

Cheers!

 

Zymomonas is a facultative anaerobe. It works with or without oxygen and grows post fermenation. It can produce sulphur, but that isn't always apparent in young beer. It can also produce acetic acid. When acetic acid is coupled with the green apple smell of acetaldehyde, it can produce a smell that is more similar to cider than green apple.

It is impossible to say for sure what is causing the problem. I just suggested two possibilities. I'd pitch less yeast, raise the fermentation temperature after 3-4 days and sanitize the tap water.

 

You left out the acetaldehyde part.

 

Do you mean the title (at the top): “m) acetaldehyde"?

I am not sure what you are getting at here.

Cheers!

 

I am studying for the written exam. There is another part in the study guide which has a lot of that, and then a part about how the beechwood chips getting the yeast out of suspension too soon and causing acetaldehyde in Bud. We know better.

That is what I though your link went to.
See page 59.
http://www.bjcp.org/docs/BJCP_Study_Guide.pdf

 

I just copied up to the part where "Zymomonas" was mentioned since that was the topic of specific interest (bacterial infection):

“m) acetaldehyde

This compound has the taste and aroma of fresh-cut green apples, and has also been compared to grass, green leaves and latex paint. It is normally reduced to ethanol by yeast during the secondary fermentation, but oxidation of the finished beer may reverse this process, converting ethanol to acetaldehyde. Elevated levels are generally present in green beer or if the beer is prematurely removed from the yeast. It can also be a product of bacterial spoilage by Zymomonas or Acetobacter…”

Yes, you and I are well aware that the Bud/acetaldehyde aspect is fiction.

Cheers!