Aeration after signs of fermentation

Ok I need an expert. Last night I brewed a 5 gallon batch, cooled it, and aerated for 40 mins. I woke up this morning and it was already pushing some crud out of the blowoff tube.... Which is too soon based on my experience (although I did used yeast that I harvested one week prior and pitched to a starter 2 nights before- don't know if that would cause it to started sooner than a fresh pack of yeast). Anyway, I was suspicious so I am thinking there wasn't much oxygen for yeast reproduction and build up.... So I took my diffusion stone - the whole aeration kit purchased from morebeer- tested it in water and there were only two streams of bubbles. I have another diffusion stone, so my question is if there's any positive or negative effects with trying to aerate right now, after signs of fermentation have started? Will it help the yeast, or has the damage been done?

Thanks a lot!

Wait. Don't you want a vigorous fermentation starting as soon as possible? I thought that was the whole point of aeration.

If it's not a big beer, and you have krausen, leave it alone, you're going to do more harm than good at this point.

Well yes and no. Once the yeast are pitched they use the oxygen from aeration to build up there cell walls and reproduce. fermentation begins when the environment becomes anaerobic, so once oxygen is all used up. So if it starts too quickly then I feel that's a sign that there may not have been enough oxygen for proper yeast build up. Now they are required to work on the entire wort with not enough reinforcements, which can strain the yeast and possibly lead to an under attenuated beer.... That's how I interpret it at least.

It's of was 1058, so not a huge beer. Plus I don't have an accurate measurement of how much harvested yeast I pitched. There may have been enough that not much reproduction was required, but my instinct tells me that that was not the case.

*OG. Sry

You aerated for 40 minutes, used a starter with plenty of viable and active yeast, and most likely met or exceeded the pitch rate needed for your beer. Smack packs and vials contain far less than the recommended viable cells for a 1.058 wort, which may be why you see a longer lag time if you usually just pitch them directly.

I frequently pitch my yeast and have blowoff in less than 12 hours. Sometimes as short at 4 hours. I aerate for about 15 minutes max, with an aquarium pump. This is with either a starter, freshly washed yeast or properly rehydrated dry yeast. I just make sure my pitch rate is appropriate and I have very few lag times that exceed 24 hours, with the exception of Hefe's.