Temp differences

[jamnw]

I have a chest freezer with a johnsons temp controller, probe is taped to glass Carboy.
Set point is 65, with a diff of 1.

Probe reads 65, but I have a temp gauge sitting opposite end of freezer at top, and it reads 72.

I hope that probe is accurate.

Curious, what do you think the temp in the wort is?

First I have used this equipment.

Thanks

 

[BrewMoreBeers]

Sounds like the air in the keezer is stratifying. I use a small four inch fan in mine to keep things stirred.

 

[Tall_Yotie]

7 degrees is a HUGE difference. Is the 72F probe near the compressor? That can indeed increase the temperature.

I would trust more so the one taped to the carboy. If concerned, stick the probe tips in boiling water and see if they read 212F or not.

 

[jamnw]

It is a digital therm I bought at Target that is reading 72.
It is closer to the compressor. But in a basket above it.

Worry a bit because I've had two batches of slug bait because of high ferm temps.
That is why I bought the freezer.

 

[Tall_Yotie]

Move the thermometers and see if there is any significant difference. All you can do now is experiment and see where the error is coming from.

 

[slamback]

I would tend to believe the probe taped to the carboy. I have the exact same setup, and have struggled with that in the past, and it seems that the taped probed was the solution. Is the other thermometer taped to anything, or just wagging in the air? I found that the "wagging" probe was highly inaccurate...

 

[jamnw]

When I got home the probe said 61 !!!

I sanitized my glass thermometer and put it in the wort, it read apx 67.

Damn.
Frustrating.

 

[cwi]

When I got home the probe said 61 !!!

I sanitized my glass thermometer and put it in the wort, it read apx 67.

Damn.
Frustrating.

There are at least two possibilities at play-
1. Your probe or thermometer, or both are not calibrated. Calibrate in ice water, not boiling water, as that is closer to your desired range of accuracy.

2. Your probe is too exposed, and you viewed the temp shortly after a compressor cycle ended. If this is the case, you are viewing the overshoot temp caused by "thermal inertia" of the freezer/fridge. This can, and should, be minimized by taping, then insulating, the probe on the carboy.

You have posted questions in several threads needing "nerdy" types to figure them out for you, including the aquarium controller thread you just commented in where this issue has been discussed at length. Part of the price of needing a nerd now and then is putting up with them bickering about who is right. Otherwise, we would all still be throwing sharp sticks to get food, and crapping in the back corner of the cave.

 

[greatschmaltez]

A temperature probe attached to a carboy and a thermometer reading ambient air are definitely going to be different base case in your set-up. Air cools and heats up much faster than 5 gallons of liquid. I have the same set-up as you do and have one of those sticker thermometers attached to my carboy and it reads within a degree of my probe. Pick up one of those sticker thermometers for like 3 bucks and then you can have direct comparison, right now you haven't measured the same thing with the probe and another instrument.

That being said, I am surprised by your wort/carboy temp being so different. Based on what I've read and my own experiences, the wort and carboy temp should be within a degree or so. You may have a temp offset, but you need to compare apples to apples. Put your prove and another temp in ambient air or a glass of water together and see if there is a difference.

 

[cwi]

The stick on "mood ring" thermometer strips are of no use in this situation, or really any situation needing precision temp readings. They are "ballpark" only.
He already has three thermometers, they just need to be calibrated before any further conclusions can be drawn.

If the controller probe is taped to side of the carboy, but not insulated, it will fluctuate a good bit. It can go well below the set point for short periods due to temp overshoot. If the door is opened, and you watch the temp, it will give a good idea of how much influence air temp is having on your probe. Even if it is well insulated, the air still influences the probe temp a good bit, which actually helps with controlling the temp of the wort better.

A controller probe taped to the side of a carboy shouldn't be treated like it is an instant read thermo of wort temps. If the temp is observed for a few minutes (well after the compressor cycles off) until it quits changing, that reading will be close to actual wort temp.