Well, it's only five hours lost....

[Inkleg]

HTBTIHAHB = Huh, That's Badass...Think I'll Have A Home Brew.

[FedoraDave]

Total guesstimate.

This was washed yeast (from a batch in which I used washed yeast, so this was second generation yeast). I had it in a 1/2 pint Mason jar. There was maybe 1.2 inch of yeast at the bottom. No idea how that translates to any kind of quantity. Then I did a starter with this yeast, and while it took its time getting going, by the time I was ready to pitch it, it had a good krausen on it, so there were even more cells by then.

[mashani]

My guess - your starter since it was from an older generation of yeast had not as many good parent cells to begin with as you normally have. Between that and the continuous aeration (which extends the growth phase by adding a needed nutrient for growth phase - oxygen), is why it took a longer time then your used to grow daughter cells before it was forced to switch to active fermentation. The less initial viable yeast you pitch, the more of the final results are going to be those spanking new and hungry daughter cells that will grow up to the nutrient limit of the starter wort. (that's why an significantly underpitched stir starter is a good way of reviving sketchy yeast, the healthy yeast make a lot more daughter cells and the sad yeast gets outcompeted - it's a not-so secret brewery trick that some use to revive yeast strains that have gone too many generations and are getting sketchy).

Those hungry daughter cells are now very happy critters. And should make excellent beer.

[FedoraDave]

Good explanation.

I've also noticed that WLP001 is a very robust yeast with very vigorous fermentation, so add that to the mix, and I'm not surprised I blew the lid off twice.

[Beer-lord]

05 raised part of my lid twice in 2 days as well. But, I did have the bucket pretty full with a lot less head space than normal.
So far, I've found aeration with an oxygen kit to produce more vigorous fermentation (just used it twice so far) but my hope is to get more attenuation.

[FedoraDave]

For my fivers, I aerate with a wine degasser attached to my cordless drill. Foamalicious!

[mtsoxfan]

It would gross out my wife if I used my degasser... so I just use a french balloon whip.... I get about 6-8" of foam....