Hi all,

I have access to a couple of thermometers at home: an analog instant-read thermometer, and a remote digital meat thermometer I use for BBQing.

similar to:
http://image.made-in-china.com/2f0j00Sv...-P102-.jpg
and
http://store.weber.com/img/ecom/product/3032908_lg.jpg

Now, I undertook to read the temperature in the top of my vacpot when I'm about to toss in the grounds, and I've gotten inconsistent temps. The digital reading around 175, and the analog around 165-170.. neither seems quite high enough. I wonder if it's because in both cases the entire length of the probe is not surrounded by water (the BBQ probe in particular is way too long).

If so, exactly what kind of thermometer should I be looking to use when I'm trying to accurately measure brew temperatures?

You're going to need to do your own investigation of those products, I think. You can easily calibrate/check a thermomether by putting it in a steam bath and verifying that it reads the boiling point for your altitude, like this.

If your thermometer reads what your boiling point is, you're good. The analog thermometer can probably be calibrated using the hex nut behind the dial. The digital one, if off, will have to be calibrated according to manufacturer's instructions (if available) or you can just memorize an offset.

Are you letting these thermometers stabilize? Definitely give them a chance to come to max reading. If you calibrate them and they read something close to 212 F (again, check your boiling point for a better number), then they won't be that far off. Most thermometers will provide more than adequate accuracy for brewing coffee; more expensive ones will just come to an accurate reading faster.

Anyway, technicalities aside, are you sure you aren't just brewing cold with your siphon? It's easy to get very low temperatures if you put the top part on and seal it before the water is hot. How's the coffee? I'd think 170F brewed coffee would taste pretty underextracted...

If you're looking for accuracy better than a couple of degrees, ignore your altitude and use the current barometric pressure if you're going to do boiling-point checks. If your local TV station doesn't give this on their website (or broadcast), try http://www.weather.gov.
I happened to check this when I was doing some boiling-point measurements, and the local barometric pressure at the time was equivalent to several hundred feet below sea level.
-Ed

shadowfax wrote:You're going to need to do your own investigation of those products, I think. You can easily calibrate/check a thermomether by putting it in a steam bath and verifying that it reads the boiling point for your altitude, like this.

If your thermometer reads what your boiling point is, you're good. The analog thermometer can probably be calibrated using the hex nut behind the dial. The digital one, if off, will have to be calibrated according to manufacturer's instructions (if available) or you can just memorize an offset.

Are you letting these thermometers stabilize? Definitely give them a chance to come to max reading. If you calibrate them and they read something close to 212 F (again, check your boiling point for a better number), then they won't be that far off. Most thermometers will provide more than adequate accuracy for brewing coffee; more expensive ones will just come to an accurate reading faster.

Thanks, I'll look into this stuff

Anyway, technicalities aside, are you sure you aren't just brewing cold with your siphon? It's easy to get very low temperatures if you put the top part on and seal it before the water is hot. How's the coffee? I'd think 170F brewed coffee would taste pretty underextracted...

To be honest I'm not sure what I'm looking for just yet.. the coffee tastes good to me. I've been half-inserting the top part (leaning in the opening of the boiling bulb but not sealing it) till I see it's ready to boil, and then I'll insert the top segment, and once it's all migrated to the top I dump in my grounds, stir, and brew for 60 secs.

Try putting the thermometer in the bottom part while you're heating it. See what it reads before you put the lid on. Depending on the vessel you use, an odd bubble here or there may be rather early. If you've already tried this, I am curious what readings you see right before the lid is sealed on.

Craig -

I think the problem you are seeing is probably a probe problem, and not one of thermometer accuracy. Both of these probes are fairly massive, and are long. So you are measuring something like the average temperature of the hot water at the tip plus the cooler metal along some length of the probe.

To get better readings with these thermometers, increase the immersion depth into the water and give them plenty of time to reach equilibrium.

Jim

decaf_Ed wrote:... ignore your altitude and use the current barometric pressure if you're going to do boiling-point checks.

I got this wrong.

These guys got it right (JimG and EricS): Calibration of Omega HH506RA thermometer
If you get your pressure from the weatherman, you want to figure your altitude back into the equation.
-Ed