I'm brewing my first batch of beer, it's a wheat beer, filled 2 separate 1 gallon carboys. Fermented like crazy for first couple days, settled out after about a week, then after about 12 days, fermentation started back up again with a new foam top and lots of bubbles. I've read it might be from temperature change which could totally be the reason, but if that is the reason, how much could that affect the beer? And also, what other things could it be? Thanks!