My having a friendly debate with my brewing partner that a kettle used only for boiling the wort does not need a thermometer since we are simply boiling, and the temperature will not exceed 212. He claims it can. Can anyone who is smarter than me help settle this?
Because of the sugar in the wort, it can get higher than 212. I’ve seen temps of 214-216. But you still don’t need a thermometer in there IMO.
Here is my simple layman’s understanding.
No, the wort will not exceed 212* because that is the temperature at which water boils/vaporizes into steam and consequently leaves your kettle if your lid is off as it should be.
Steam can be heated to a greater degree because there is no other state for the water transform into beyond gas (AFAIK). Same is true in the opposite direction, pure water will not get colder than 32 before it turns to ice.
I’m not sure how much more or less that boiling point is affected by our wonderful wort additions. Not terribly much I would expect.
That said, it can be nice to have a thermometer in your boil kettle when chilling your wort.
I agree with denny that the the boiling temp for wort is above 212. But that doesn’t really matter. The wort is going to boil at a certain temperature and you can’t exceed it. (Although it will rise if you boil off enough water. )
The reason I like having a thermometer in my BK is so that I know when it’s getting close to a boil. When I am waiting for the wort to boil I am usually doing other things like cleaning the mash tun. The thermometer let’s me know at a glance when it’s near boiling so I can keep an eye on it.
A much better reason to have a thermometer in the kettle.
I agree with what has already been said.
Another factor (useless fact? you choose), again very minimal, is atmospheric pressure. Water boils at 212 deg F at sea level. Go up from there and the temp decreases. Go down from there and the temp increases to overcome the increase atmospheric pressure. this happens very slowly so you can normally assume boiling is 212F unless you are on a ridge above Denver or sitting at the bottom of Death Valley you won’t really see much variation. This is why vacuum liquid reduction works to make wort extract with minimal caramelization.
Paul
You sure of that thermometer calibration? At 30 Brix and 99% purity this gives a 0.31C increase. Maybe hop particles help elevate the temps.
I will have to check with the thermopen while I do an upcoming Barleywine. I don’t remember seeing anything too high when boiling, but I don’t usually brew over 1.110 OG beers.
I’m at about 1000 ft, boiling is 210F. Denver is 202F. At Sean’s brewery in Leadville, he will be boiling at 193F.
I have a thermometer in my brew kettle. It is nice to know when the boil is approaching, and is very useful when using an immersion chiller to see when you are at pitching temp.
Dissolved solids (e.g., maltose and other grainy stuff) will tend to increase the boiling point of water above 212 F. Elevation also comes into play. I would expect that at sea level you could experience a boiling point of 213-214 F. At higher elevations, no, it probably won’t happen. Bottom line is that it’s always going to be someplace between 205 and 215 F, and the behavior and reasons for doing the boil are all the same regardless, so… this is truly trivial knowledge and nothing more. I don’t put a thermometer in my boil kettle because I can tell by looking at the wort what it’s doing. With experience, even during heatup I can tell approximately how much longer it will take before it hits full boil. I’ve noticed there seems to be a point around 160 F or thereabouts when the sweet wort makes a lot of strange popping noises as if it’s boiling deep down on the bottom, then that goes away but a protein foam begins to form on top. The closer you get to a boil, the more foam there is. Then 5 minutes later, the foam falls back in, and you can crank up the heat as high as you want without fear of boilover. It’s the foamy part of heatup and boil where you get your boilovers. Yadda yadda yadda…
Cheers.
Regardless of small changes due to altitude and dissolved sugars though, the temperature will never exceed that adjusted value. There are other reasons to have a thermometer, but you don’t need one.
But if you’re gonna glance at the thermometer, why not just glance at the kettle to see how it’s doing? The lack of a thermometer on my kettle has never interfered with my ability to judge when it’s gonna boil.
It’s calibrated at mash temps so it could be off at boiling.
Perhaps a thermometer could read slightly higher because at a full boil, a portion of the probe is in contact with steam. Maybe. I guess you could test this buy turning off the flame and seeing if it immediately drops a degree. Just imagine how trivial that knowledge would be. 
+1. Never had one on my kettle. I’ve had one boilover in 20 + years. The sticky mess to clean up was a good teacher.
of course it can. and you don’t need a thermometer for your boil.
it is the same phenomenon that allows water to be colder than 32 degrees when you put salt in it.
in addition. if you find a way to pressurize your boil vessel you can superheat it above 212 degrees with out boiling.
I can, and frequently do look inside the BK. But it’s nice to be able to keep an eye on it from across the garage. It’s not like I added a thermometer just so I can watch the temperature. My BK is a Blichmann so I’m just using what’s there.
I am a single kettle kind of guy. I use the thermometer when heating strike and sparge water, as well as cooling.
I biab so need the thermometer. Also @ 5000 ft my boil is steady @ 202 degrees
Don’t feel bad. I have Brewmometers on all three of my kettles. On cold brew days I don’t have to blow steam out of the way to see if it’s boiling yet. Plus it’s handy for watching chill temps.
Having said that, I believe it is entirely possible to brew beer without any thermometer. All you need is a pencil for math and a way to accurately measure water. It’s helpful to know what your well water temp is too.
So for me, 10 lbs room temp grain in 4 gallons (1.25 well temp + 2.75 boiling) equals about 150°. Prep sparge water the same way. Bla bla bla. But until Jonathan’s thermometer eating zombies attack, I like my three brewmometers.