I was under the assumption that the yeast needed oxygen. That is why you are suppose to stir it daily or twice daily. Wouldn't an airlock tend to deprive the yeast of oxygen since the space would fill with gas rather quickly if it is a good fermentation.
Yeast do need 02 to thrive. That being said if you have ample room in your primary and give it a good stir in the beginning and about every other day or every day a few times if there is fruit in there then you will be giving it plenty of 03. Ive been using an airlock on primary for around 8 years now with no problem at all.
troy , my big deal with the lid and air lock is mostly my dogs LOVE wine!!!! also i dont want random flys to get in , or for dust to settle and the most common wold be Lab Fur!!! i swear they shed a puppies worth of fur daily!! the lid an airlock keep it out very well for me.
Like said before, some of us have different circumstances like young children and rodents or bugs or animals like cats that will get into anything. I have the cats and everyone has bugs. The bugs can be remedied by a cloth with an elastic or something to keep it tight.
I put a cheese cloth that has been folded over several times over the primary and then sit the lid loosely on top of the bucket. This works okay for me. I've never found bugs in my wine and my cats leave the wine room alone in general unless I'm in there.
I throw a towel over the primary and set the lid on top loosely.
Not only are you introducing the outside as Troy said, but the yeast are using dissolved oxygen in the must. When you stir you are mixing oxygen into the must. There is CO2 on the surface during fermentation and that is preventing oxygenation and also protecting the wine.
Cover with a cloth etc. Fine, but putting a lid on it seems to me to inhibit any oxegen entering to help the yeast "grow", and just cancels out the whole idea of the cheese cloth, save the cloth and do the lid anyway.
Guess I am really wondering is just how much oxegen is required to ensure a successful ferment?
So if we have no cats, no kids and no nosy friend or inlaws, WHY, even bother with the lid? Just leave the cloth on it.
Many people have had great successes with leaving a lid on the primary with an airlock. Many have never used an airlock at all during the primary.
I have to wonder, and we'll leave this one to LUC. if anyone has ever done a controlled experiment trying it both ways.
Are there differences in TEMP, so2, etc.
If the end result was to be the same, then I wonder why this would be a question at all.