using old yeast cake for new brew

[akueck]

I've been brewing for about a year now. I'd like to reuse the yeast cake at the bottom of the carboy for a second batch of another beer. Will pouring the new wort into the carboy oxygenate the mix enough or should I give it a real good stir? When I usually pitch yeast, I leave the carboy open for 15-20 minutes before putting the airlock on. Does the same rule apply when I'm "pitching" onto the old yeast cake? Anything else I should know?

[BillyBock]

Yep, pouring into the carboy should be sufficient. Since you're reusing a yeast cake, they really don't need a charge of oxygen as they already have their population. You'll find that they get to work right away--no lag phase for growth here! Watch out for an explosive ferment.

v/r
Bill

[akueck]

So how explosive are we talking? I'm only going to fill the carboy a little more than half full (small batch), so there should be plenty of headspace. Or is it the gas release rate that would be the problem, not the foamy stuff?

Thanks,
Aaron

[BillyBock]

We're talking VIOLENT...foam everywhere. Make sure to leave plenty of headspace and use a BBBOT (big bore blow-off tube). You should be ok only filling it half way. The BBBOT (about 1" diam) should be routed to a small bucket of water as an airlock--use this configuration until things calm down. Otherwise a regular airlock could clog and pressure would build up inside the carboy, which may not be safe.