Starting brewing: vent the brewing container to help the yeast reproduce?

[Oh mad one]

A total noob question. Just wondering, but suppose you've just mixed your "mash" (or your liquified extracts, as the case may be), added water, spray malt and yeast, and are ready to just leave the brewing container in a suitably warm and dark place for fermentation.

Would it help to leave the fermenter unsealed, i.e. with a small aperture, given that yeast requires oxygen in its reproduction period? Or would it be preferable to seal off the container, and judiciously open it every few days to allow oxygen to mix with the culture?

Thanks in advance

 

[ceejam]

Hopefully you mixed throughly and ‘aerated’ the wort sufficiently to introduce enough oxygen for the yeast to get going.
Common guidance on here is to leave the lid cracked slightly to allow CO2 to escape, once fermentation starts.
You don’t want to be opening the lid as you could risk bacteria getting in and causing an infection!

 

[terrym]

The wort should be vigorously aerated before the yeast is pitched, especially if most or all of it has been previously boiled as in all grain brewing, which then allows the yeast to multiply in the early stages of fermentation.
There is then normally no need whatsoever to further aerate the brew, since the yeast does not require further oxygen for it to function, in fact late on it could cause oxidation of the beer which is unwanted.
It is normal homebrewing practice to leave fermenting beer covered or sealed but with an escape route for CO2 produced in the fermentation process. Typically an air lock would be used. Howebrewers do not leave the fermenting beer uncovered, as in some traditional brewing processes.

 

[Oh mad one]

Thanks for the great explanation guys! Most helpful.

Yes, last night I Googled a lot, and decided on leaving a little hole open to allow CO2 to vent.
It seemed to have paid off this morning, as, when I peered into the hole, there was already a thick layer of foam on top of the mix! It happened sooner than I expected. The yeast seems very happy in there. It smells like a Supermalt factory though.

Just one more question: I appear to have lost more liquid content to evaporation. Would it be a silly idea to top it up with a bit of boiled water?

 

[Madhouse]

Just one more question: I appear to have lost more liquid content to evaporation. Would it be a silly idea to top it up with a bit of boiled water?

You can, but it will impact on your final beer. My knowledge on this is a little limited but I'd say you could add (sterile) water post-fermentation although it would lower your ABV and probably thin your beer in terms of taste and mouthfeel.

Personally I'd chalk it up to experience, work out how to adjust my next brewday and look into getting an airlock.