I was thinking about using open fermentation with a Saison in June. The main reason for using open fermentation is that it increases esters and phenols correct? Can anyone think of any reason that open fermenting a Saison would be undesireable?
I do it because it's easier. But, it's just laying the lid on the bucket during the attenuative phase. Once that is past I'll snap the lid down if not transferring immediately to some other vessel. With a carboy one could just cover the mouth and neck with a piece of foil.
As a caveat, you don't want to leave your fermenter "uncovered" generally. I ferment in chambers so the buckets are still protected from ambient air movement. Leaving one out with the lid off will almost certainly result in contamination.
I read years ago about pressure affecting the esters and whatnot. Doesn't seem to matter at the homebrew level, though had a saison's krausen drop immediately one time when I pressed hard on the lid of the fermenter. Despite that the beer was fine.