Fermenting 7.5 gallons in 8.7 fermenter w foam control?

Do you think .5 gallons of headspace will be efficient with fermcap foam control and temp control?

Yes, especially if the fermentation temperatures are controlled and the temperature stays under 70 degrees. It seems like a hot fermentation can get more explosive than a fermentation at proper temperatures.

I don't think I ever have more than 1.5 gallons of headspace, and I don't use Ferm-cap. I've never had a problem, except one time when my temperature control was not in place and it got above 75 degrees, in a wheat beer. What a mess!

Thanks

It will depend on yeast health, and type of yeast.

FermCap does not seem to do anything to Belgian yeasts. If you have a healthy pitch with a Belgian yeast, it will blow-off with a 0.5 gallon head space.

I use FermCap and have slowly been reducing my headspace. I've gotten to around 0.5 gallons (in a 7 gallon fermenter) and have started getting blow-off in every batch, when I didn't before. It's not much, but enough to fill the airlock, and if I don't get to it soon enough will plug the airlock and blow it off.

I'm back to using a tube on every batch again. I don't lose any beer (except for Belgians) as the foam does not get high enough in the tube to go out the other end. I use a swamp cooler to keep temperatures in check.