Temperature in different parts of the wort (insulated fermentation bag)

[tiredofbuyingbeer]

Recently, I acquired a new fermometer. Since the old one was on the bottom of my fermenter and a little crooked, I placed this one near the top of the same fermenter so that I could more easily see it. I brew with my fermenter in one of those Cool Brewing bags, so it's easier to see the decal when it's higher on the fermenter.

Interesting observation: there's temperature variation between the two fermometers. Usually, it's 2 degrees; once it seemed to be up to 4. Both fermometers are the ones that have squares that light up with temperature degrees, and give you three lit up squares to illustrate the range of temperatures you beer might be fermenting at. The higher fermometer is always at least one square warmer than the lower one, or about 2 degrees.

It didn't occur to me before that temperature may vary in different parts of the wort, or that this might be significant. I would assume that the reasonable response is to treat the fermentation temperature as the average of the two readings, but I guess something could be said for taking the higher of the two, since yeast in that region might be throwing off more esters. Pleasant surprise, in my case, because I suspected I might have been fermenting too cold.

I'm pretty sure this phenomenon occurs in my case because I use frozen water bottles inside of an insulated bag for temperature control. The bottles never sit well straight up, so they're usually tipped over on their sides, which means that they cool the bottom of the fermenting wort first before the top. Note that the water bottles are not actually touching the lower fermometer; I realize that will throw off the temperature it reports.

 

[mongoose33]

Is the water touching the lower fermometer?

In my brews there's always a lot of convection going on so it doesn't seem like you'd have that much variation in temps unless the two strips simply read differently.

When you're done with this batch, store your fermenter with the strip side down so they're both lying at the same level and see if, after a while, you get the same temp. It's the only way to see if they're truly reading the same.