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Older carboy thermometer strips

I bought two carboys second hand that came with a thermometer strips on the side of each. When I first got them “several months ago” I remember checking them to the ambient basement temp to my lab thermometer and was surprised how accurate they were. Since then I haven’t paid much attention to them as my basement was right around 60-62 all winter in NY. I’m improving my note taking ten fold now which is whats generating this question. So I filled the one carboy yesterday and it was going wild last night/right now. I used wyeast 1028 with a temp range of 60-72 I believe; SG was 1.062. Used Mr. Malty pitching calc and made a 1.040 1.7 L starter a day before (Intermittent shaking). The empty carboy says 68 which my lab thermometer says 67. The full carboy rocking says 75 glowing into 78. This worried me so I sanitized another bung, lab ther, and paper clip. After hanging the thermometer into the fermenting beer for at least 5 minutes I pulled it out quick and it read 72. I then left it in for about 30 minutes and checked it again at 72. Has anyone seen results like this? The carboys were from a lady who’s husband died 7 years ago so they are old. But why would they have been accurate before and the one is not now? I’m not sure if they are like the ones on NB that people report breaking after washing; I have washed them every time I clean it out. Could this affect temp reading fluctuation at different stages? I measured it also so the test line on the lab thermometer was fully submerged. I also just bought this lab ther and checked it against a ice bath and it was right on and same when the wort started boiling. Overall I feel I should trust the lab thermometer. I have also had some trouble finding a chart or some sort of equation to estimate temp raise at full Krausen? If anyone knows of a data site that shows SG/ambient temp/pitching rate/to high krausen temp with FG involved I would be interested in that.

I did a back-of-the-envelope calculation and found that 5 gal of average-gravity ale will have an average temperature differential of 4.5°F over the course of active fermentation. So 10°F at high krausen isn’t unreasonable. Higher gravities, higher pitching rates, and higher starting temperatures will all increase the temperature differential.

This is the primary reason why it’s best to pitch a few degrees below your target fermentation temperature.

Is there a “hold” function on your thermometer? Or are you able to read it while it’s actually submerged? If not, I’d trust the LCD strip over the thermometer.

Its just a glass thermometer. I can’t read it while it’s submerged at least not with the krausen. I have never seen it drop 3 degrees in the split second it takes for me to pull it out though. It seems to be rather slow when it gets right to the last degree or two.I have been debating on getting a digital one. Just so many tech goodies I want and keep putting them off to do more batches. I usually chill to about 85 (the temp I can reach before my yards a lake) and then let it sit till equilibrium is reached. I pitched this one when the thermostrip said 71 so that was probably another antsy mistake.

Fermentation generates quite a bit of heat.

To get the temp lower, once you have the chilled beer in your carboy, place the carboy of beer in a bucket of ice water. You can get them temps down into the 50s easy that way if you need to.

Yepers, fermentation generates heat. Only way to keep it at or below ambient temp is to submerge it in a tub of water with some frozen soda bottles.

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