Fluctuating Fermentation Temperatures

I searched through the forums for this but couldn't find anything. I apologize if this has already been covered...

Having just brewed my second batch, I noticed the temperature of the wort as measured by the lcd thermometer on the side of the fermentor fluctuating between 70-72 during the 1st three days of fermentation. On the 4th day the temperature dropped to 68. The same thing happened in my first batch, which after the first 3 days has maintained a constant 68 in both primary and secondary. The room my fermentors are in is kept at a constant 70.

I'm not worried or concerned, but just interested that both times the temp actually increased and then fell below ambient room temp after the initial activity. Anyone else see anything like this?

Thanks!!

During active fermentation the temp can raise up to 10 deg.

That's pretty much standard behaviour for the yeast. As they eat the sugar they generate heat and it'll go above ambient for awhile. The slightly cooler temp is probably from not heating up from the night. If your fermenter is glass, glass is a poor conducter of heat so it stays cool for a long time.

EvilTOJ said:

That's pretty much standard behaviour for the yeast. As they eat the sugar they generate heat and it'll go above ambient for awhile. The slightly cooler temp is probably from not heating up from the night. If your fermenter is glass, glass is a poor conducter of heat so it stays cool for a long time.

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Not to mention 5-6 gallons of fermenting beer. Water is very unconductive of heat. For my pilsner, it took about 24 hours to get from 20C (68F) to 12C (55F) with an ambient temp of about 11-12C.

Thanks all for the info!!! It makes sense that yeast releases a given amount of heat

I'm using a plastic fermentor. Having more consistent temps is a good excuse to get one that's glass.

Being a new brewer I like running across all these little bits of information that I haven't found in anything I've read.

Thanks!!!