Sudden Temp Rise

[JStans12]

I currently have two beers fermenting with WLP001. They have both been in primaries for about 15 days. Everything normal for the first 12 days. The temperature hovered right around 64F with a couple degrees of variation. Primary fermentation appeared to be wrapped up and the yeast had dropped almost entirely off the top of the beer.

Then on day 12 our apartment started to get cold, i noticed the temps had dropped to about 58F so i shut a window and about 12 hours later they were way up to to 75F. I didn't expect to have any issues but now one of my beers has all kinds of activity going on inside it. There is a patchy white foam on top and the airlock is bubbling every couple of minutes. I'm trying to figure out if this is bacteria or yeast. And I'm also wondering if this sudden increase in activity was due to the temp change. I would appreciate any input from someone who has had a similar experience.

I can't currently take a picture of the fermenter. The foam is extremely white, more so than any yeast I have experienced but it isn't fuzzy (yet). It's patchy and covers about 50% of the top of the beer.

 

[pernox]

While it's possible that your yeast is finishing up, the most likely scenario is that your beer is just gassing off. Warm liquid holds less CO2, so as it warms it will release some of what's left in suspension from fermentation. Also, heat causes expansion, which equates to airlock activity. I suspect that your other batch may be doing the same thing, but not showing airlock activity due to an imperfect seal.

 

[JStans12]

Thanks! Gassing off makes a lot of sense. However, I'm not convinced of the imperfect seal theory. Are there any other theories as to why to why this is only effecting one beer? The one that's gassing off is a super hoppy red ale and the other is a chocolate stout. Both had OG of about 1.050.