Soy Sauce Fermentation - Is open fermentation necessary?

[TheSkilletHead]

First of all, I know that there's unlikely to be anyone here with direct experience in soy sauce - speculation, assumptions, and opinions are all welcome and requested.

I've been searching for a few days on how to make Soy Sauce and have turned up a few results around the web, most notably here: http://forums.egullet.org/topic/103707-making-soy-sauce-at-home/

You basically boil and grind soybeans, make a dough out of that and flour, grow mold (I'll add cultures of Aspergillus oryzae, the preferred soy sauce mold), toss the moldy dough into a brine, ferment for one to many months outdoors in the sun, and strain. For some reason, every source I saw had pictures of an open fermentation, though nobody specifically specified that an open fermentation was necessary or beneficial.

I can assume that being outside in the sun will both evaporate the alcohol and reduce the brine. However, I am at a loss as to why everyone does an open fermentation.

I can think of a few reasons for an open fermentation:

1. It's just a mix of tradition and the equipment available. (A closed fermentation would work just as well)
2. It's beneficial for natural bacteria and yeast to make it's way to the brew - it adds character to the sauce.
3. It's exposes the brew to oxygen.

I would prefer to do a closed fermentation to better control what is and isn't in the soy sauce considering I'd have to leave it outside for a few months, but I should be able to make open fermentation work if necessary.

Can any of the experienced brewers, particularly those who do lambics (and have some experience with natural yeast and bacteria), chime in on their opinion of an open fermentation for soy sauce?

If an open fermentation is preferred, would it be preferable to use a bucket or a small glass carboy (with a smaller opening), assuming both would be protected from rain water and bugs?