[rbclay]

You know- the stick on type that you put on a carboy. I used to think these were pretty accurate. I now think they are junk. I pitched a wort that I thought was 58F, according to the fermometer. I thought I gave it (the fermometer) time to adjust from an empty bucket (ambient temp) to the temp of the wort. After I pitched I decided to temp the wort with my thermocoupler. I got 48F! So I decided to look at my other fermometers. I have one on every bucket and carboy. I HAD 3 EMPTY PLASTIC BUCKETS SITTING NEXT TO EACHOTHER IN THE SAME ROOM. THE FERMOMETERS HAD 3 DIFFERENT READINGS! 62-66F. WTF?
I have a bitter fermenting in the same room. Fermometer on that bucket reads 66F. I temped it with the thermocoupler- yep it was actually 57F! Seriously?!? How can a beer that has been fermenting for a week in a room with an ambient temp of 65F be at 57F?

Of course now I think every beer I ever made fermented at a lower temp than I thought or intended. But I have made some good beers. Some really good. Now I feel like I have to put an asterisk next to all my log book temps!
When I get home I must calibrate my thermocoupler. That is the only thing I haven't done yet. I can't believe it would be off 10 degrees...

[tygo]

I was thinking about the experience you had posted earlier this week so I tested my fermometer on the beer I brewed this morning against a reliable glass thermometer I hung down into the wort prior to pitching.  It was right on at 58F.

My experience has been that they're pretty reliable.  Something to keep an eye on though I guess.

[Hokerer]

I was thinking about the experience you had posted earlier this week so I tested my fermometer on the beer I brewed this morning against a reliable glass thermometer I hung down into the wort prior to pitching.  It was right on at 58F.

My experience has been that they're pretty reliable.  Something to keep an eye on though I guess.

+1, My fermometers have also proven to be pretty accurate

[Pawtucket Patriot]

I have to agree that mine are pretty accurate too.  In fact, I just chilled my amber ale down to 63, measuring with a dial thermometer I calibrated this morning.  When I transferred my chilled wort to my fermenter, the fermometer read 63-64.

[rbclay]

I do have a couple different brands/types of fermometers bought at different places over the years. Perhaps I need to do further testing. Is it wrong that I want to leave work early so I can go home and test this stuff? Of course not, silly question.
Hey, I might as well just brew another batch tonight, right?!? I thought so...

[a10t2]

How do you know your thermocouple is correct?

[breslinp]

Fermometer on that bucket reads 66F. I temped it with the thermocoupler- yep it was actually 57F! Seriously?!? How can a beer that has been fermenting for a week in a room with an ambient temp of 65F be at 57F?

Could the thermocoupler be the one that is wrong?

[rbclay]

Just tested the thermocoupler. It's fine. Did an ice water bath (33F) and boiling water (211F). It does have a +/- 2 range. If that thing was off I'd drink a Bud... no probably not.

Pesky fermometers. Know what? This is the most perfect RDWHB moment ever. I realize temp control is the perhaps the most important thing next to pitching levels. I know my system well enough and make very good beers that I doubt this one incident with this one fermometer is enough to worry about.

So let me start another thread on the postivie and negative of fermenting ale yeast slightly below their "target range" in their description. Maybe I've been fermenting colder all along. In general, fermenting slightly below the cold end of the range would be less detrimental than going to the other extreme. (Belgians excluded). I use basically 1056, and several British strains.

[tom]

Are these the horizontal or vertical ones?

I think the horizontal ones used to be very accurate, but could be affected by getting wet.

[rbclay]

Horizontal. Upon closer inspection I have 3 distinct styles of fermometers. I have decided that the oldest ones (10 years old) need to be replaced. The others are newer and seem to be more accurate. I won't discount their use entirely, just need to rely on a thermocoupler reading before I pitch.

[tygo]

Yeah, I was wondering if it might not be an age thing.  Mine are only a few years old at most and most of them are less than a year old.  They've got to wear out eventually right?

[Bret]

I just replaced mine.  The old ones were still on and completely inaccurate. Somewhere along the way they were submerged in a cooling water bath and I think it compromised their accuracy.

[Pawtucket Patriot]

I just replaced mine.  The old ones were still on and completely inaccurate. Somewhere along the way they were submerged in a cooling water bath and I think it compromised their accuracy.

I used to have a few fermometers that got submerged in a swamp cooler several years back.  Their accuracy was completely compromised.  So, I spent a couple o' bucks replacing them and the new ones are very accurate.

[TheWineBrewer]

Hey I got a great video on how to read Stick on Thermometers here: https://www.youtube.com/watch?v=IBb2q2GI3pY

[erockrph]

Agreed on everything here. My fermometers have all been dead-on in agreement with my IR thermometer, up until they've gotten submerged for any length of time. For the price, they're one of the most useful tools in my brewery.

I wish someone would invent a fermometer that I could use for my mash and strike water. They're nearly as accurate as the majority of thermometers I've used for measuring those temps, and are certainly within the window of "close enough for government work".