Boil with lid partially on - some venting

[ArcLight]

In BrewChem 101, the author writes that one can conduct the boil with the lid partially on (more than just a crack - at least several inches exposed), enough to let the DMS and other compounds escape, but also covered enough that some of the vapor will hit the lid and condense, running back into the kettle.
He also says that at time one should remove the cover, to allow a full boil off.

The advantages are less evaporation and with a weak burner (i.e. stove top) it's easier to maintain a boil.

The disadvantages are not enough DMS and other compounds escape.

Any thoughts on this?
Any literature on this?


Mods - If this belongs in the General discussion then please move it, I placed it here because this is a Physics question, with a scientific answer, not a "I do it this way" type of question.

 

[DPBISME]

Have always thought you needed it off, just from reading I am no expert. Even at the end of my boil I doing cover it when cooling until vapor quits rising.

I would think you could take a chunk of cloth, in the center tie a string, then hang it over the pot so it looked like a "dunce" cap; to retain heat.

The vapor would soak into the cloth, when it got dense enough it would dribble down the cloth and away from the beer.

The only think I can see as being an issue is where does the water go,,, we don't want it to put the burner out.

OR

Boil longer

OR

Splurge and by yourself a "real" burner. I have two of these though I got them cheaper than this http://www.campchef.com/maximum-output-single-cooker.html

It works fine for ten (10) Gallon batches and will get 13 Gallons wort way past a modest "rolling boil"