Air lock activity restarted after 2 weeks

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silentC

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First post, sorry if this is an FAQ, I checked but couldn't see it.

I put down a brew on the 21st of November:

1.7kg Morgan's Iron Bark dark ale
1.5kg Morgan's Master Malta Lager
Hallertau and Cascade teabag hops

Normally I would use a colder temp yeast but as it's warmed up, I used the kit yeast. SG was 1040 @ 26 degrees.

Primary fermentation started during the night and it went mad for a couple of days then stopped (airlock activity). On 30/11 I checked SG and it was 1018, then on the 4th it was down to 1016. When I checked it on the 4th I noticed there was a small amount of airlock activity and since then it has taken off again. I was going to bottle it over the weekend but I think I should leave it for a bit longer.

Question is, has anyone had it kick off again like that for no apparent reason, and why do you reckon it happened? I don't think the temperature has changed that much and it has been sitting at around 24% on the fermenter whenever I've looked.

I've done probably a dozen of this recipe, but using an ale yeast, and usually it is a bit slow to get going, then takes off after a couple of days, then tapers off and arrives at final SG within 9 to 12 days.
 
I'd be concerned about an infection, fermentations can continue for a while, but they rarely jump back into activity like you see at primary.
 
How does it taste and smell? What is the gravity sitting at?

One of the earliest lessons you learn in brewing is to ignore the airlock, it doesn't tell you anything useful and more often than not leads you up the garden path.

If the brew had warmed by a few degrees, even after fermentation had finished, you would get some CO2 coming out of solution and possibly starting up the airlock again.

Take a sample, test the gravity and have a taste. If they are all where they should be and you've had 2 gravity readings the same over 24-48 hours then bottle (or keg).

By all means keep using an airlock, but only your hydrometer should be used to tell you anything about fermentation and whether it has finished.

JD
 
Yeah taste is fine and no obvious bad smells. It was just weird that I thought it was nearly done and then it started bubbling again after nearly 2 weeks. I've never had one do that. I usually do ignore the airlock, other than liking the sound of it plopping away in the middle of the night, which I find strangely reassuring :)

I'll check the hydro again tonight. I usually bottle this one at 1014. Actually I just went back through my records and I did one with the kit yeast back in February. It was 13 days in the fermenter and I bottled it at 1012.

We've have some weird weather here the last week or so - most likely it has warmed up without me noticing.
 
At the end of fermentation there's quite a bit of CO2 gas dissolved in the beer. The amount of CO2 retained in the beer (and not vented off into the atmosphere) is directly related to the temp of the beer and atmospheric pressure.

The colder it is, and the more pressure its under, the more CO2 the beer can hold dissolved in solution.

So, like JDW81 said, airlock activity in a finished brew is to be expected if the temp of the beer increases. And you say you've had some "weird weather" lately - would that also mean a low pressure cell passing over? If so it might also explain CO2 gas coming out of solution and escaping via the airlock.
 
Yeah we've had thunder storms the last few afternoons, cold and gloomy one minute then hot and humid. I'll put it down to the weather.

SG is 1014 tonight at 23 degrees. If its unchanged by Wednesday I'll bottle it. I used to worry about leaving it in the fermenter too long but I've left brews three weeks and they've come up fine.

I did a ginger beer recently and SG was still falling after 4 weeks. It got down to 990 something before I lost my nerve and bottled it.
 

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