Fermenter temp vs fridge temp

[Tulsahomebrewer]

I am brewing a Hefeweizen and recommended fermentation team is 65-68F. I am using a wine fridge to control temp, and it is set at 60F. But the stick on thermometer on the fermenter shows 74F. I have tested fridge with a thermometer inside it and it is pretty stable at 60-61F.

So my question: when they say recommended fermentation temp should be 65F, does it mean the temp inside the fermenter (including heat it is producing)? Or is the outside temp in which the fermenter is placed?

Thanks!

 

[davidabcd]

I am brewing a Hefeweizen and recommended fermentation team is 65-68F. I am using a wine fridge to control temp, and it is set at 60F. But the stick on thermometer on the fermenter shows 74F. I have tested fridge with a thermometer inside it and it is pretty stable at 60-61F.

So my question: when they say recommended fermentation temp should be 65F, does it mean the temp inside the fermenter (including heat it is producing)? Or is the outside temp in which the fermenter is placed?

Thanks!

It's meant that the temp inside the fermenter should be kept within the yeast's range.

 

[eric19312]

It's meant that the temp inside the fermenter should be kept within the yeast's range.

+1 on this

Also I suspect either your stick on thermometer is wrong or perhaps some sort of user error. A pic might help see what is going on.

It is not unusual for the fermentor to be at a higher temperature than the air around the fermentor during active fermentation. Active fermentation actually creates heat. The faster the yeast activity the more heat created. Many yeasts will ferment faster and faster as temperature increases so the problem is compounded. The ideal fermentation temp for the yeast to make beer of a favorable flavor profile is likely well under the temperature that the yeast will grow and eat fastest, so once temp starts to rise it is pretty easy to see the temperature spike to well above the ideal temperature.

Your set up requires the heat from the fermentor to be transferred to the air in your wine fridge, and when the thermostat on the wine fridge notices the air temp is over its setpoint then the fridge comes on until air is back to set point.

The rate of transfer of that heat from the beer in the fermentor to the surrounding air depends on a lot of factors including for example the fermentor material and thickness, the difference between the air temp and the fermentor surface temp, whether the air in the fridge is still or being mixed, and the volume of the fermentor. The rate of transfer is important, if the transfer is too slow then the heat may build up in the fermentor and you get the spikes.

All that said I do kind of doubt that you have a 14F temperature difference between your presumably small (6 gallon or smaller?) fermentor and the air in a wine fridge. You could see that if you put the beer in the fridge warm and were reading current temperature and it is still on way down. Or your sticker could be defective or you could be reading it wrong.

I suggest you get an inkbird controller (or similar) to control the wine fridge. Tape the probe of the controller to the side of the fermentor and place a piece of insulating foam over the probe. Plug the wine fridge into the Inkbird. Set the Inkbird to turn the fridge on when the fermentor is above 66F and set the wine fridge to cool the air in the fridge to 60F. Check to see if your wine fridge has a fan to circulate the air. If not add a small computer fan running off a USB power supply. SHould be able to watch the temperature of the fermentor on the Inkbird and if you are still spiking above 68F set the wine fridge to go a little cooler when it gets turned on. If you see temps on the inkbird dropping below 65 on a cooling cycle then set the wine fridge to go a little warmer on its cooling cycle (maybe 63 is fine).

Sorry for the wall of text hope this is helpful. You should know there are quite a few brewers who make great beer without getting obsessive about temperature control but since you are already down the rabbit hole you might as well join us obsessives...

 

[mongoose33]

Typically we might expect yeast to raise the temp of the fementing wort 5-10 degrees above ambient temperature. That's why it's best to control temp either with a temp probe in a thermowell, or pressed against the side of the fermenter and covered with insulation to isolate it from ambient.

I use these to do that on my fermenters; I also use an Inkbird 308 as @eric19312 suggests above. Couple of pics, one showing the 1" foam I use, the other showing it held in place against the fermenter. BTW, I have both blue and pink foam, so I'm gender-neutral here:

 

[Tulsahomebrewer]

Thanks everybody....for now I have decreased set point to 55F, will see if that helps. If not, I will think about buying an inkbird. I have to share my current wine fridge with the wifey, so need to keep it tidy! Have you guys drilled a hole in the fridge to snake in the temp probe or just squished it between the door?

I have a 3 gallon fermonster in there now, with 2 gal wort. This also tells me that my first two brews did not ferment at the ideal yeast temp (warm fermented pilsner and doppelbock) , cause I was always trying to keep ice bath at about 60F and stick on thermometer was showing about 74-76F.

 

[TechFanMD]

I highly recommend putting a fan in there when using it for this. The temp setting for the wine fridge is probably pretty good, but with little airflow, the area of the thermostat in the wine fridge may be cool, but with no air moving another area can be quite warm. Just a 12v PC fan with a wall wart power supply will do good enough.

 

[RM-MN]

Thanks everybody....for now I have decreased set point to 55F, will see if that helps. If not, I will think about buying an inkbird. I have to share my current wine fridge with the wifey, so need to keep it tidy! Have you guys drilled a hole in the fridge to snake in the temp probe or just squished it between the door?

I have a 3 gallon fermonster in there now, with 2 gal wort. This also tells me that my first two brews did not ferment at the ideal yeast temp (warm fermented pilsner and doppelbock) , cause I was always trying to keep ice bath at about 60F and stick on thermometer was showing about 74-76F.

If your water level was near the level of the beer when using the ice bath, the beer was pretty close to the water bath temp. Check the beer temp with a different thermometer to see if it really is the same as the stick on thermometer shows.

 

[mongoose33]

Thanks everybody....for now I have decreased set point to 55F, will see if that helps. If not, I will think about buying an inkbird. I have to share my current wine fridge with the wifey, so need to keep it tidy! Have you guys drilled a hole in the fridge to snake in the temp probe or just squished it between the door?

You probably can just snake it past the gasket; do it on the hinge side of the door, and you should be ok.

I actually have drilled a hole in my fridges to allow the probe wire to pass inside without the gasket being compromised (though it's not much compromised at that).

 

[Tulsahomebrewer]

5 hours after bumping set temp to 55F, fermenter temp is holding steady at 66F. It is fermenting like crazy right now, so I’d assume that the fridge is able handle it.

Just checked the fridge inside, it has an inbuilt fan that runs almost nonstop.