How the heck did you manage that? Fall asleep during the boil?
LoL!
I was making a large, 4 gallon batch of 1.086 concentrated starter wort to be frozen in 1.5 quart containers. Using 100% Pilsner malt, only combining 1st and 2nd runnings* to keep initial gravity higher, I set out for the routine 90 minute boil to drive of DMS...
In hindsight, that long of a boil is not really needed for starter wort, we're not making beer for drinking. It's actually counterproductive for starters, not helping with good wort fermentability.
Anyway, it was moving along fine, at first. But due to the lowish starting volume plus the higher gravity, while I must have evaporated more and faster than planned. The next time I'm checking with the refractometer, I'm a bit puzzled: where the
heck is the line...? Oh there it is, on the very top... 1.115!
Worked out fine though, needed fewer containers, saves freezer space. And so far seems to work fine for yeast starters.
* The 3rd runnings, around 1.030 IIRC, were boiled much shorter, just by themselves, chilled and used for starters right away, a good gallon worth.