Half Batch, Normal Fermentor

I just bottled my BPA, and had almost immediate fermentation. My guesses would be either the wort wasn't properly aerated or maybe the smack pack wasn't actually healthy. I've never used wyeast, so im talking out of my ass and just throwing darts at a wall. Is there any krausen? With all the extra space, maybe there isn't enough CO2 to make a difference in the airlock

 

I do it all the time for my 2.5-3 gallon batches, the fermentor size is a non issue. Could be a long lag time. What temp is the beer fermenting at?

 

maybe it's just not perfectly sealed. I have one bucket that NEVER shows bubbles in the airlock, but always produces fine beer. I think it's just not sealing quite right around the rim.

 

CO2 will push out the extra airspace and create a bigger blanket of CO2 than you'd get on a 5 gal batch. As it's in plastic and you may have a leak, get it into bottles/keg shortly after you hit FG.

 

My last 3 batches have been 3.5 gallons fermented in a 6.5 gallon carboy. The initial headspace won't matter in the first 24-48 hours as the will absorb some/ yeast will "fart" co2 which will push out remaining oxygen once fermentation gets strong. With more "headspace" might take a little longer for the co2 to buildup and bubble than a carboy filled to the brim. As each fermentation is different, I would wait another day for signs (i.e. yeast on top, trub, bubbles) . How old was the yeast? Perhaps it lost some vitality. If after 48 hours, I would sprinkle some dry yeast in and shake it up. Good luck

 

When you say healthy, does that mean it was swollen when you pitched it?

 

Take a gravity reading, its the only way to determine fermentation. The airlock isn't necessarily an indicator of fermentation.