Is yeast kicking up into full gear after 4 weeks in primary a bad thing?

I usually don't freak out about these things and really am not concerned. I'm more curious of the outcome. I whipped up a Motley Brew IPA with a bunch of leftover hops. The OG was 1.060. It went through the normal ferment and finished up about 2 weeks later. I let it sit another couple weeks for the hell of it.

Yesterday, I went to rack and whoa... it kicked back up and a krausen re-formed. It makes sense. I recently put a tripel in the same room and boosted the temp in the room to 73. This has never happened to me. A few of my buddies are convinced it's infected. Other's aren't. I don't think its infected but I am curious if others have experienced this and what was the result. Please share your stories

What makes you think it kicked back off? Visible krausen? Is the gravity dropping? If there's krausen, does it look like yeast or something else? More info like SG, temp, etc. would be helpful.

NordeastBrewer77 said:

What makes you think it kicked back off? Visible krausen? Is the gravity dropping? If there's krausen, does it look like yeast or something else? More info like SG, temp, etc. would be helpful.

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Ya I mentioned there was a krausen, the temp was bumped to 73 and the OG was 1.060

The gravity was sitting at 1.020 yesterday but I haven't checked it today. It's definitely going. Big chunks of yeast are visibly moving up and down and airlock activity every 6-8 seconds or so.

I'm really more interested in if this has happened to others before and what was the outcome of their beer. Did it finish ok? Anyone ever have an infection? It's more of a curiosity question.

Yeah, I was actually referring to fermentation temps before you bumped it up to 73. And the reason I asked about gravity was cuz if it's not dropping, it's probably not fermenting. The reason I asked about krausen is because warming up a fermenter can cause co2 to come out of solution, rise to the top and bubbles as it leaves the liquid.
You say the gravity is stable around 1.02, unless it drops some more, your beer isn't kicking back off, it's releasing co2 cuz it warmed up and warm liquid holds less dissolved co2 that cool liquid.

NordeastBrewer77 said:

Yeah, I was actually referring to fermentation temps before you bumped it up to 73. And the reason I asked about gravity was cuz if it's not dropping, it's probably not fermenting. The reason I asked about krausen is because warming up a fermenter can cause co2 to come out of solution, rise to the top and bubbles as it leaves the liquid.
You say the gravity is stable around 1.02, unless it drops some more, your beer isn't kicking back off, it's releasing co2 cuz it warmed up and warm liquid holds less dissolved co2 that cool liquid.

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Ya that makes sense and I probably should have given an update on the gravity. It's at 1.016 now. I've seen degassing before since I routinely leave my beer in primary for a month, but this was different. The yeast are definitely movin and groovin. It started at 64, slowly rose to 70 and sat at 70 until I bumped it to 73. Btw, I'm talking liquid temp here not ambient. I have no reason to believe its an infection but if it sours, I'll bottle it and drink it anyway.

Seems to me 1.02 is a bit high of a FG for a 1.06OG. 1.015 or so would be 75% attenuation which is pretty normal, of course depends on a lot of factors. I suspect that things stalled out or was going real slow at 1.02 and the rise in temp got it going at a good clip again. I doubt that this is a real problem other than possibly having saved you from overcarbed or possible bottle bombs.

I've noticed that many yeasts get lazy at the end of fermentation and sometimes crap out prematurely, but if you raise the temp about 5 degrees it gives them a kick in the butt to finish the job. In the summer it's easy just to raise a brew to room temp to do this, but in the winter when your house temps are cooler its not as easy. I set the fermenter on a plant seedling heat mat which bumps temps up to the low 70's (for ales) for a few days to finish out fermentation.

I find that even yeasts like Cali ale yeast can get sluggish and take a while to finish, but when you give them the temp boost at the end they finish quicker and drop faster.