Well I visit my daughter who lives at about 8k feet and the water boils at 180Where in Colorado are you visiting a town that's at 17, 000 feet elevation? That's the point at which water boils at 180F.
According to The wisdom of the internet, Leadville is the town with the highest elevation in the US at 10,430 and BP of water is about 193F according to a calculator. Denver would be 202F or so. Not an insignificant difference from the normal 212F but not 180.
Interesting question, though...I think we have do a beer swap between low-landers and high-elevation brewers using the same recipe and same hops so we can compare head to head.
Isomerization starts at 180
But, wait!!! In the equipment profiles, there's a box to fill in for elevation...That should account for boil temp and difference in IBU calculation.
This is not like flipping a switch. I'm not sure of an exact temperature like 180 F or anything else but I get the feeling that some isomerization can happen as low as like 140 F or maybe even 130 F, it's just very very slow at these temperatures. About 170-180 F is a common range to extract a lot of flavor with not so much bitterness while preserving many aromatics that will in fact boil off above around 180-190 F.
I guess if it does, it does, calculators be damned!!!
would the boil off rate be affected as well? Not that I plan on moving there, or going to a higher altitude to prove or disprove the calculator’s accuracy.I guess if it does, it does, calculators be damned!!!
There's an IBU calculator here on the site that accounts for elevation and it definitely shows lower IBU contribution for he same amount of hops boiled for an hour. Isomerization may start at 180 but I guess the percentage of utilization increases with temp.
So... your original question of temp vs time is valid and I think the answer that you just have to calculate a different percentage of utilization. It would appear that a 1 hour whirlpool or hopstand at 180 would definitely contribute to IBU total but substantially less than a 1-hour boil at 212 or even a hotter temp in the whirlpool or hopstand. It stands to reason that if water boils at 180, it won't get to a higher temp without pressure. Utilization percentage doesn't seem to be built into the recipe calculator and requires an input, based on estimate I suppose.
I propose an experiment next time you're in CO. Try boiling a gallon of wort as usual with a measure of hops and do the same with a gallon of wort under slight pressure to raise the temp. If you could get a direct taste comparison of bitterness between the two temps, it would really illuminating.
The difference in 10 percent of the IBU total would mean 5 points out of 50 in a pretty hoppy beer. In lagers and blondes, more like 2 or 3 points. That's probably not enough to really mess with the flavor too much. Easy enough to adjust with boil length. Just brew as instructed and leave the kettle on for an extra 5 or 10 minutes before flameout and chill. Whirlpool would be same percentage of isomerization no matter where you are.
