Proper way to measure temperature

[Mike613]

Hi all,
I have done some searching for an answer to my question but have not quite found the answer.

First a rundown of my equipment. I do partial mashes in a little 8 quart cooler and boil in a 5 gallon kettle. I use a standard thermometer (long stick with round dial on the end).

My question is, what is the proper way to measure the mash water temperature? For example, I need to heat a certain volume of water to exactly 170 degrees. Depending on where the thermometer is in the pot the temperature varies greatly sometimes up to 20 degrees. I get similar results using a heavy duty stainless steel pot. I stir the water and then take a measurement, but I am still not comfortable as to what the actual water temperature is.

Am I needlessly worrying? Do I get the water to what I think is the right temperature, dump it in the mash tun and wait for the mash to drop to the desired temperature before putting the lid on?

Thanks everyone. I have learned a ton from these forums so far!!

 

[the_bird]

I can't imagine having a 20° variance in water temp. When I bring my strike water to temp, I just measure near the top of the surface and it's fine. The heating process is making the water swirl around anyway, you shouldn't even need to stir. You aren't hitting the side or bottom of the pot on any of your measurements, are you?

It's a good thermometer you use? I use a $10 digital pen thermo from Target, it doesn't take long for it to get a good reading.

 

[Mike613]

It seems like a decent thermometer - purchased at LHBS.

I stir because the water sitting directly over the fire on my gas stove is hotter than the rest of the water. I could be entirely over-thinking this.

 

[the_bird]

I think you are.

The water that's directly over the fire is going to rise up to the top of the vessel and the heat be disbursed. If you're worried about that, turn down the burner when you take your reading, give it a stir if you think it'll help. If you go a little high, that's fine, as you noted you'll add it to the mash tun and you can wait for it to lose a little heat before adding your grain.