Off flavor/odor from cold break

Question

On page 63 of Brewing Better Beer, Gordon Strong says,

Some of the cold break material can actually help the yeast, but too much can contribute off-flavors.

I can attest to both of these. A couple of times I have,

• pitched
• let the trub settle for a couple of hours
• racked the really clear wort to a fermenter

Since I was left with a bit of trub that had a bit of nice wort in it, I fermented a bit of it in PET bottle. The fermentation took off extremely fast. But the resulting "beer" had a pretty nasty smell.

My question: Can anyone tell me what the off smell/taste from excess cold break is? Is it one of the common ones, like diacetyl, acetaldehde, etc.? I couldn't identify it, but it was pretty distinct. I often detect this same aroma at bottling time, but it always goes away soon after bottling.

Answer 1

Great question on a topic that I don't think is discussed much by homebrewers since we tend to stick to ales. This is a more significant issue for creating clean lagers..or at least a more obvious problem in lagers when present.

Greg Noonan's New Brewing Lager Beers is about the only place I've found a solid discussion of the topic. On pp 170-171:

"Proteinaceous precipitate from the hot and cold breaks forms the greatest part of the trub. Although amino acids are absolutely necessary for yeast metabolic functions, yeast react to an excess of simple protein by generating aromatic fusel alcohols...Fusel alcohols are subject to esterization, which produces fruity and solventlike odors that are inappropriate in a lager beer, and to oxidation, forming "stale"-tasting aldehydes.

Trub also contains polyphenols, ketones, and sulfur compounds that may be absorbed into the ferment. Polyphenols give astringent-tasting, mouth-puckering flavors. Volatile sulfur compounds (H2S, DMS, thiois, and mercaptans) produce rotten-egg, skunky, onionlike, rubbery, and burnt-match flavors and odors."

So, that's quite a list of bad stuff you don't want in your beer and just because a hoppy, fruity ale might be better at covering it up doesn't mean it isn't still there! Doing what you can to minimize break material (hot & cold) making it into the fermentor seems worth-while in all cases.