Temperature reading problems in a ferminator.

[pablobobo]

Mad swings in temperature readings here, first time using this piece of kit.
So the probe is insulated fairly well with yoga mat material, touching the side away from the cooling unit.
I've seen anywhere between 18 and 26 degrees so I'm really confused as to what the thermometer is actually reading. It's been in for about 3 hours.
The fermenter is cold to touch, and the side thermometer is reading 18- is my guess as its so hard to see any colour on the strip.
Any ideas folks, is the beer too cold now and the reading is off? Can I sanitise my thermometer and stick it in to check?

 

[Gnomebrewer]

Even with yoga mat taped over the thermometer, the air temp will affect the temperature reading. I'm going to have a guess here that the air temp in the unit is getting super cold trying to bring the beer temp down? If so, that's why you'd see temperature swings. Let's say the beer's at 21C and you're aiming for 19C. If the unit's set on a straight on/off type switch, it might chill the air down really low, say 2C before the thermometer gets down below 19C, so the unit switches off. That cold air keeps affecting the thermometer so the temperature reading keeps dropping, even though the beer might not drop by as much. So the thermometer might read 16C which is actually 20C beer and 10C air. Eventually it settles and reads closer to the beer temp again, so the unit switches on and undershoots again, but there should be less of a swing the second time. Eventually it should even out (if it's working properly). There are ways around it if you're worried - you can run a PID temp controller (it's smarter - it learns how to minimise over and undershooting temperature) or run a second temp controller to measure air temperature (set it to prevent air in the chamber from dropping too far below your target beer temperature) or you can put the temp probe directly in the beer using a thermowell.

Yes, it's OK at this stage to use your sanitised stick thermometer to check (assuming it's still early in the ferment; try to limit opening the fermenter later, to avoid oxidation).

And welcome to HBT!

 

[pablobobo]

Thanks for the awesome reply! I think you're right, it's just taking a while to settle. I sanitised a thermometer and stuck it in there, 15C, the probe reads 17. So, not ideal, I'll give it the night and check in the morning with an update.

 

[Gnomebrewer]

That's OK, pitching cool and allowing your beer to come up to ferment temperature is good. I'm going to assuming you're aiming for somewhere around 18 to 19C? Assuming to room the fermenter is in is warmer than that, if your chamber's working properly it should come up close to your target temperature overnight. Because you're pitching cool, expect it to take at least 12 hours, probably more like 24 to 48, for the first signs of fermentation.