Thermometer Recalibration

[Garrete]

I was bored and wanted something brewing related to do. So I thought, re-calibrate my thermometer. I filled a glass with ice. Added water and put in my thermometer. I let it sit for a few min. then added a few more ice cubes. I then let it sit for 5 min. When I checked on my thermometer, it was reading 40*. I took out a pan and filled it with water and began to boil it. Inserted the thermometer into the boiling water and got 212*.

What do I do now? I thought set it for the lower temps, but I need it for my mash temps. I also need it for my wort temp before I pitch.
Do I get a new thermometer?

Thanks

[BadRock]

From what I can tell water should boil around 210 at your elevation. Thus your thermometer is off by 2 on the high end. Also you may have to add salt to your water to get your fluid temperature down to 32. I always try to use another thermometer as a reference on both the high and low end. You can pick up a lab quality thermometer at most LHBS.

This site will help you calculate your boiling point.
http://www.virtualweberbullet.com/boilingpoint.html

Happy Brew'n!

[fermentalist]

No, no salt--the colligative properties will mess it up--fill glass with ice and allow ice to melt 1/2 way in fridge say over an hour. Then the water in it will be 32.

[Bugeater]

My many years of working in professional kitchens has required me to calibrate thermometers hundreds if not thousands of times. The ice water method requires a thick ice slurry. That is, fill the glass with water just enough to get the ice to start to float. Alternatively use shaved ice with a little water. The ice itself is colder than 32 degrees, but 32 is as cold as water can get without freezing.

Do not add salt to the water. 0° F is defined as the coldest you can get a salt saturated solution without it freezing.

For my brewing thermometers I take a little different approach. I do have a lab grade mercury thermometer that I picked up on eBay. I had a friend in the physics department at the Univ. of Nebr. check the calibration on it and it was dead on. I heat some water to around 150° and stick both my lab thermometer and the thermometer to be calibrated in it. I then adjust the thermometer to match that on my lab thermo. I don't care whether it is right at freezing or boiling temperatures, only mash and pitching temperatures. This pretty much guarantees that.

Wayne

[fermentalist]

Right, the salt will actually cause the freezing point to be depressed--hence why salt is added to icy roads--and the slurry will actually be colder than 32 degrees if salt is added.

Just adding ice to water is insufficient guarantee that equilibrium exists, obviously if left out in a room, the ice will all melt and water may never get close to 32, hence the suggestion that the melted ice occur near freezing as in a fridge.

Good point about the additional point at mash temps where accuracy is important. For not too much money, narrow range thermometers can be bought covering the zone of interest with better resolution. Good digital thermometers these days are not bad at all, I had one specced againt a standard and it was +/- 0.6 F from 110 to 170. No worry about breakage!