Secondary fermentation caused by dry hopping?

[Jayjay1976]

I recently brewed a clone of Beau's Lug Tread Kolsch, OG 1.050, pitched WY 2565 and let it ferment four weeks until it was steady at target final gravity of 1.011, then dry hopped with 1oz Azacca and 2oz Mandarina Bavaria. Within a few hours I saw activity again in the airlock, which is not unusual, but it continued to bubble steadily at a slow rate for ten more days until I bottled yesterday when I measured an FG of 1.006!! It smells great and the sample tasted good, but I'm wondering if some wild yeast or diastaticus was introduced by the hop pellets.

 

[Smellyglove]

This is not uncommon. Apparently it DH can introduce some enzymes.

 

[Qhrumphf]

It's often called "hop creep" and is a well known phenomenon, due to small amounts of enzymatic power in hops.

If you do a chemical analysis of a beer pre and at multiple points post dry hop you can observe a decrease in RE, observe a conversion of that RE from varied polysaccharides to maltose, a rise in ABV, production of CO2. and a resurgance of diacetyl and/or diacetyl precursors. Basically unfermentable sugars and dextrins get broken down to fermentable sugar, and then residual yeast ferment them.

To what level and in what timeframe seems to be highly variable, but certain hops seem to cause it more than others. I experience it regularly with Cascade. Papers have been written studying it with Centennial. Mosaic is reportedly fairly enzymatic as well. There's been a push for hop growers to include enzymes in available lot analysis, but that might be a while before that's a regularity.

It's well discussed in pro circles (where a dry hopped beer could potentially overcarbonate in the package and has to be closely watched for).

Why it never trickles down into homebrew knowledge is beyond me.

 

[Queequeg]

Another good reason to dry hop during primary fermentation

 

[Qhrumphf]

There's been a few ways to work around it. My preferred is to dry hop towards the end but while fermentation is still occuring (though late fermentation, not early on during highly active fermentation as I would do in a NEIPA). Doesn't stop the creep but cleans it up faster.

Others have proposed/tried reducing dry hop temp to a level where the yeast won't be active (often lower 50s). May work for kegged product, but anything bottled/canned (even if it's force carbed) poses a problem until it's filtered/pasteurized/always stored cold. Once it's warm any viable yeast mean potential problems.

It's a frustrating phenomenon for sure.

 

[Bubbles2]

Also did you really reach the Yeast's Final Attenuation Percentages? 10% makes a difference. Some Yeast go to 80% others knock off at 70%. Free Yeast like you asked about, I highly doubt are not going to be able to survive that ABV, as yeast needs to be grown to lift that 'weight'. Free Yeast could, after a long conditioning "maybe" add an off flavor, but oxidation would be more the culprit in that case.

 

[couchsending]

1.011 to 1.006 is a rather big drop from hop creep. 1.011 to 1.010 or 1.009 is more normal.

 

[Qhrumphf]

1.011 to 1.006 is a rather big drop from hop creep. 1.011 to 1.010 or 1.009 is more normal.

Typically yes. But I've personally seen a 1P drop at least a handful of times so it's not an unreasonable theory, especially if the particular hops were abnormally enzymatic. Of course, spoilage organisms are possible too. Or perhaps the OP just dry hopped before it actually reached FG. Or a measurement issue (poor temp correction, inconsistent reading against meniscus, sticking to the side, bad refract correction, something like that).