Brewing Master » Brewery » Digital Thermometers
Digital Thermometers
Question:
: I’m tired of my floating dairy thermometer. I don’t think it’s : very accurate and it’s definitely slow. : Has anybody found a good source for an inexpensive .1 deg F : resolution 30-220 range digital thermometer? My local homebrew store sells a digital thermometer for $15. It has a metal probe about 5" long and the thermometer part is about the size of a digital watch. It’s great, although I learned an important lesson while making my first ever all-grain batch: Don’t ever, EVER get the top part wet! I had to take it apart and dry it in a panic in the middle of mashing. — | Software Technologies | Disclaimer: HP doesn’t agree with | Vancouver Printer Operation | this. Or maybe HP does. | Hewlett Packard Co. | It depends. | Vancouver, Washington (USA) |
Response:
One thing to look for is the accuracy of the thermometer. Most of the low priced ones I’ve seen advertised list accuracies of +/-2% of full scale. For a 0-100C (32-212F) thermometer, that’s +/-2C or +/-3.4F (total error 4c or 7.8F). That may be too wide a range for mashing. One thing in your favor, though, is that the error is usually consistant (i.e. always +2.3F +/- some smaller error). If you can find out what that constant error value is you can compensate for it. If you can get access to a calibration thermometer (see post about William’s Brewery in this thread), you may be able to find the correction factor. Now, before I get totally flamed, There is some error in the floating dairy thermometers that are in common use (including my own brewing process). I don’t know what the accuracy is of these units are, but I’d like to. If they aren’t any more accurate than the low-buck digitals, I’ll go out and get one tomorrow. I have never made any attempt to calibrate the one I use, I just trust it blondly (Freudian slip). I just tested it at freezing and boiling and it said what I thought it would. If anyone knows more about the accuracy of the dairy thermo’s, please post.
Response:
I have compared various handheld themometers to a very accurate Type K thermocouple probe by Omega Scientific that I use experimentally at work. The rated accuracy of this probe assembly is +/-0.2^C. The comparisons indicated that lab grade mercury themometers were quick to respond, and highly accurate given the relatively small spatial metering that is done visually (ie, the calibration marks between adjacent degrees can only give about 1/2^C precision). However, the use of mercury based sensors in foodstuffs is problematic, given the toxicity of mercury. When I made comparisons to floating dairy, meat and dial thermometers there was consistently some perceptible level of offset — +2.5^C in the case of the dial probe, and -2^C in the case of the floater. Interestingly, the meat thermometer was slightly more accurate (approx. -1.5^C). It should be noted, in all cased, the temperature reading of a sensor indicates the temperature of the SENSOR, and not neccesarily the medium in which it is placed. Further, using the digital probe illustrated that without vigorous stirring of moderately thin mashes (or using a RISC system) mash temps throughout the grain bed are highly variable, sometimes in excess of +/- 5^C within a few centimters. All those using relatively slow reacting sensors are urged to allow the thermometer to equilibrate in the mash, then move it vigorously around the tun, thus accomplishing spatial averaging, to get an idea of mean temp throughout the mash. Also, a good lab grade mercury thermometer can be had for about $20, and although you might not want to use it for general measurement, it will work well for calibration. –Cheers Dave
Response:
I’m tired of my floating dairy thermometer. I don’t think it’s very accurate and it’s definitely slow. Has anybody found a good source for an inexpensive .1 deg F resolution 30-220 range digital thermometer?
Ryan, Taylor and several other companies now make high quality digital thermometers. The price about $20USD. Two common sources I have found are: Speciality cooking shops and commerical kitchen equipment suppliers. Btw, I have also found a pencil-style pH digital Ph Meter very helpful in getting the mash pH at 5.2. However at $50USD they are still a bit pricey, but very easy to use. I found mine at a chemical supply house. If you buy the pH meter, also purchase the indicators for calibration. Cheers Pete Give Yeast a chance.