Thermapens - me again
- missclawdy Feb 23, 2013 12:52 PM
I have written before about my Thermapen that registers temperatures between 150 degrees and 160 degrees when the Tenderloin I am cooking was just past the Blue stage.
I am inserting the tip of the probe from the side and into the centre of the fattest part of the meat.
It registers 212 degrees in boiling water.
At this point, I am confused more than anything. it seems the thermometer is working properly but why would the reading for the beef be so off?
It may depend on where, exactly, the thermocouple tip is within the metal probe. If the tip of the thermocouple is 0.5 cm up from the tip, then the temperature you're measuring is 0.5 cm away from where the tip is. You could figure out exactly where the tip of the thermocouple is by preparing some ice water (and give it a while to equilibrate to 32F), give a god stir, and put just the tip into the water. It should read 32F. If not, move the probe down a couple of millimeters. You'll find the point where it reads 32F. This should give you some idea of where the tip of the thermocouple is. You can also do the same routine with boiling water.
Getting accurate temperatue readings isn't as easy as it sounds. The thermocouple on most probe type thermometers is in the first couple of mm. On a tenderloin, I would measure the thhickness and then make some type of mark on the shaft of the Thermapen to indicate the halfway point. You can go from the side or top to bottom, it shouldn't matter. The key is to go deep enough but not too deep, that's why a mark on the shaft will help you. You can use a piece of masking tape like a little flag. If it's reading 212 in boiling water, then it's definately close, a degree or two depending on elevation.
Just parenthetically, the boiling point of water varies more than a degree or two. It drops a bit under 2°F for every 1000 feet of elevation. Here in Mexico City (7400 feet) water boils at 199°. It's quite a difference.
At any rate, yeah, assuming missclawdy is near sea level, 212 is spot-on. It's also good to measure ice water to see if it's calibrated at the other end.
Do you have another probe-type thermometer against which you could make a comparison? If you find a discrepancy, you could then contact ThermoWorks and consult with them on the issue, armed with some evidence. I understand that their customer service is pretty good. Even if you can't make a comparison, you should still call them and ask them for ideas or suggestions. They may be able to tell you if it is something you are doing, or if indeed it seems that the Thermapen is wrong.