Turns out this is a very interesting question.
If the keg is submerged, you’ve got a lot more water to heat up, and while some will evaporate it probably won’t boil while you’ve still got alcohol in the keg.
If the water is a little BELOW the keg, it will BOIL, and in a well designed baine marie, will condense and give that heat to the keg. So you don’t have to heat as much water, and can access the extra energy delivered by vapor.
Which makes it go quite a bit faster…
I don’t have enough hrs on this particular still to give you useful data like how often do you need to top it up. It was literally what I could throw together while we waited for parts so I could build something more appropriate. It’s buried in bikes out in my shop somewhere atm.
Edit: shit wrong still.
Yeah lot of hrs on RSOsie. She would absolutely have run more efficiently if set up as described, she wasn’t. There wasn’t enough vertical hight in there to have the water below the keg and still covering the heating element.
I thought you were referring to her younger cousin Maria.
It was probably @tweedledew who clued me in on the right way to run a baine marie