Calibrate!!!!

Sorry to yell, but I've brewed at least two 25g batches at unknown mash temps. I have Ranco digital controllers on a More Beer recirculating system. There are also analog thermometers on the HLT and Mash Tun. I'd noticed that the analog and digital temps weren't quite jiving, but it was always during mashing, and by the time I finished brewing and clean-up, I'd forget to check back into it. So today I decided to get some ice water out there and calibrate. The analog was off by 2*. The Ranco was off by 15*!!!

Shame on me for not noticing that big of a discrepancy. But I'd started paying attention to just the digital since it controlled the pump. Lazy...

Turns out that a hidden section of the cord to the probe had melted nearly through. Not enough to give me an error reading, but enough to somehow skew the temp. I replaced the probe, adjusted the analog, and all is well. But I can't help but wonder how this will affect my last two beers. They both hit their numbers (OG and FG), and are tasting okay. But I can't help but think that mashing 15* too cool would cause some issues.

Please calibrate your thermometers. It's like backing up a hard drive. You know you should, but don't always follow through. Ugh.

FYI
Using an ice bath to establish it's reading correctly at zero is pretty much useless. Calibrate always at the temps they will be used. Keep in mind also that thermocouples are rarely that accurate unless they are checked before each use. If you use them always go with a GE brand fine wire T type with the welded and sealed end. They are the only ones we use for accurate and long lasting temp readings. They still need to be checked against a high accuracy probe to determine the offset prior to use at the range you are measuring.

Thanks for the advice. It sounds like you're using these probes in a setting that's a little more demanding than what I'm doing. The Ranco probes are pretty decent, so long as the wires aren't melted through. And calibrating with ice water is about as good as it's going to get for me, and I think it'll be close enough. When the probe was replaced, it, my HLT probe, and the 2 analog thermometers all read the same.

the main message is to not assume, and don't be lazy. Just take the time to calibrate once in a while. It's cheap insurance.