Checking thermometer with boiling water

So today, I was creating a starter for my Saturday brew day and I thought I'd check my digital thermometer while bringing the water up to boil. I had a pot of plain filtered water on my burner and I had the digital thermometer stuck in through the lid. I noticed a few bubbles showing at about 210.5° and by 212° there was a good bit of bubbling going on. However, I left the thermometer in the pot and I noticed that the temp went up to 216°.

So my question is, does this mean my thermometer is off? I had read somewhere that after water reaches the boiling point it is very hard to get it to increase in temperature (takes a lot more energy). Just for reference, I am at about 450 ft. above sea level.

Not true, Water boils @ 212F but can increase beyond that within reason. I would say 4F is within reason.

There is a limit to how high a temp can be reached with an open top boil. What that is IDK and I am sure it depends on a lot of different factors but I know it is not high enough to sterilize anything. For that you need to increase pressure with an autoclave or pressure cooker w/ 15# weight.

Zamial said:

Not true, Water boils @ 212F but can increase beyond that within reason. I would say 4F is within reason.

There is a limit to how high a temp can be reached with an open top boil. What that is IDK and I am sure it depends on a lot of different factors but I know it is not high enough to sterilize anything. For that you need to increase pressure with an autoclave or pressure cooker w/ 15# weight.

Click to expand...

The limit at sea level is 212, at higher elevation you'll have a lower boiling point. The only way to increase the boiling point is to pressurize it. This is ignoring superheating from lack of a nucleation point, but that's outside of this discussion .

This will explain it: Boiling point - Wikipedia, the free encyclopedia

BenDover said:

This will explain it: Boiling point - Wikipedia, the free encyclopedia

Click to expand...

OK, that gave me a brain freeze (but seriously, thanks for the info)