Thermometer calibration
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[edit] Why is thermometer calibration so important?
In the case of cooking beef or pork to 54.5°C-55°C core temperature for longer periods we have to navigate between the Scylla of safety (min. 54.4°C to prevent toxin production by clostridia) and the Charybdis of overdoneness (in my experience a peace of beef loses its pink color and juicyness when cooked for substantially more than the recommended time according to Douglas Baldwin’s tables [1]. So if we want to cook to 54.5°C we are only 0.1°C away from the ominous 54.4°C, and thermometer tolerance plus waterbath temperature oscillation should not add to more than ± 0.1°C. At lower temperatures precision is not so crucial as you are in the "danger zone" anyway and have to restrict cooking time to less than 4 hours, and at higher temperatures you are at pasteurizing temperatures anyway.
[edit] What thermometer to buy?
You need a working thermometer with an immersion probe which should have a relative precision of 0.1°C or better, and you need a reference thermometer to calibrate your working thermometer in regular intervals. On the lower end of the price scale you may use a basal temperature thermometer (reading to 0.01°C from 32 to 43°C) as a reference, and on the other end of the price scale you may use a "Control Company Traceable® 4000" traceable to NIST standards (Precision 0.001°F, accurate within ±0.018°C) or the like. A bimetallic coil thermometer is not a satisfactory device for measuring food temperatures! See http://www.hi-tm.com/Documents/Bimet-pic.html
[edit] How to calibrate your working thermometer
Using a Traceable® 4000 or the like: let your PID-Controller stabilize your waterbath at 55°C and measure its temperature with both the reference thermometer and the working thermometer and write the results down in your thermomater calibration logbook. Apply a note on your working thermometer indicating what the real temperature is when your working thermometer indicates 55°C. Using a basal temperature thermometer: let your PID-Controller stabilize your waterbath at 32°C, take measurements with both thermometers, and repeat the same procedure at least at 43°C, even better at a few more intermediate temperatures to get a more reliable regression line and correlation coefficient. Now plot your measurement pairs and extrapolate to 55°C (you may do this with an excel sheet [[2]]). Write the results down in your thermomater calibration logbook. Apply a note on your working thermometer indicating what the real temperature is when your working thermometer indicates 55°C.
--PedroG 23:20, 4 June 2009 (UTC)
