Analogue thermometer calibration adjustment

[Cptn_Needa]

Hi
Hoping for a bit of advice on adjusting analogue thermometer readings following a 0 - 100 deg C reading check.
Checked my thermometer the other day and the ice test read as zero but the boiling test read as 104 deg C.

While I imagine that the error of the reading is not quite a linear scale, would it be reasonably safe to assume that to get to target temperatures I can multiply the required temp by 1.04 to get to the reading that will show on my thermometer?
I.E. if my target temp was 75 then I'd need to get it to 78 on my thermometer (75 x 1.04 = 78)?

 

[strange-steve]

With probably all aspects of homebrewing I suspect that "close enough" is almost always good enough. In fact I can't think of anything that requires much precision, so I reckon you'll be fine with that

 

[Cptn_Needa]

Thanks @strange-steve
It's kinda what I thought initially but (being relatively new to the AG game) I was thinking about mash temps and thought that a few degrees here or there could make a difference. At this point I started to overthink things

 

[strange-steve]

I was thinking about mash temps and thought that a few degrees here or there could make a difference.

Well you're right, it can make a difference to the FG, but really a couple of points either way probably won't be too obvious in the taste. Plus it's actually quite difficult to get an accurate reading of mash temperature anyway.

 

[Cptn_Needa]

Cheers @strange-steve
You’ve set my mind at ease

 

[Clint]

I don't half faff about with the thermometer when mashing...mainly stirring it all together then testing all round the tun to see if there's much variance.

 

[trevorS]

I tried to take my body temperature with my thermometer Seems I have had hypothermia for a week now!

 

[lancon]

For the scientists to answer - Cant you get superheated water? Does a litre of water heated to 100C immediately move to steam promptly at reaching 100C? (as observation deems water to be boiling bubbling away) and yet stays in the pot. Would the continued heat source not continue to raise the water temp?

 

[Clint]

Don't pans boil dry? I think the water "bubbles" because the heat makes it vibrate and it's reverting to gases..

 

[strange-steve]

I'm not a scientist but boiling temperature is dependent on pressure, so water will boil at higher than 100c if the pressure is greater than 1 bar. Under normal circumstances water will not get hotter than 100c no matter how long or how intensely it is heated which makes it very useful for thermometer calibration.

 

[RichardM]

For the scientists to answer - Cant you get superheated water? Does a litre of water heated to 100C immediately move to steam promptly at reaching 100C? (as observation deems water to be boiling bubbling away) and yet stays in the pot. Would the continued heat source not continue to raise the water temp?

No, the continued heat source turns the water to steam.

 

[GeorgieV]

For the scientists to answer - Can't you get superheated water? Does a litre of water heated to 100C immediately move to steam promptly at reaching 100C? (as observation deems water to be boiling bubbling away) and yet stays in the pot. Would the continued heat source not continue to raise the water temp?

I realise this is a bit off-topic but I couldn't stop myself... Yes, you can get superheated water. It happens if you heat up the water under high pressure (e.g. pressure cooker) and then depressurize it very quickly. At that point the water would have stored some extra heat. So it will continue boiling even without an external heat source until it reaches an equilibrium state. The equilibrium state could be either full evaporation or partial evaporation with the rest of the water cooling down below 100C.

 

[eyuptm]

Boyles law?

 

[kelper]

would it be reasonably safe to assume that to get to target temperatures I can multiply the required temp by 1.04 to get to the reading that will show on my thermometer?

yes, definitely.

 

[terrym]

For the scientists to answer - Cant you get superheated water? Does a litre of water heated to 100C immediately move to steam promptly at reaching 100C? (as observation deems water to be boiling bubbling away) and yet stays in the pot. Would the continued heat source not continue to raise the water temp?

Yes read this
Superheated water - Wikipedia
But I think it's more a technical term. That said it can happen in the home when powerful microwaves heat water, as the entry explains, and that's why you are advised to delay removing a container of heated water for few seconds at the end of the heating cycle in case there is sudden and explosive boiling action.