Does wort really put out that much heat?

Previously when I tested the temp of my new lagering fridge it was at 48 deg F at the warmest setting. I put my first lager in there last night and now, almost 24 hours later, the temp is at 55 deg F. Is that all due to the heat generated by the yeast??

I turned the temp controller down a bit to see if I can get it closer to 50, but anyways I'm sure 55 will be better than the 75 I've been brewing at heretofore.

5 gallons of liquid had a lot of thermal mass. If the temp of the wort was much higher than the internal temp of the fridge, the air temp will equalize at some point between the two and over time will begin to drop to the controlled temp. I use a liquid chiller as a fermentation cooler and it will equalize and drop to set point much quicker because of the similar materials.
Monitor your temps because I think it will come down to the set point within a short period. I would also tape the temp probe to the side of the carboy/bucket and insulate the probe a little. That way the controller is reading the temp of the liquid that you are trying to maintain instead of the air temp. That will keep the compressor running longer as the temp drops and keep it from cycling as much.

I saw a 4-5 degree differential with my lager fermentation. I set the stat at 52 and pitched at 52, when fermentation kicked in it got up to 56 so I had to dial back to 48 on the thermostat until fermenation slowed, then I raised it back to 52 and the wort settled at 52. I could see with my infrared thermometer how much warmer the carboy was than the surrounding area and my kegs which were at the air temp.

That's also why I tape/rubberband my controller's probe to the side of the fermenter. The air temp in the container is always going to be lower than the actively fermenting wort. My barleywine ferment was running 10F higher than the ambient in the fridge.

Is that all due to the heat generated by the yeast??

Click to expand...

Most likely.

I'm reading the temperature of a glass of water on the top shelf in the fridge. Without the fermenting wort it was 48. Over the past week it started at 55 and has slowly worked its way down to 51 where it is now. So it sounds like the actual wort is a bit higher than that. Well, I hope this will still count as a lager.