How much is too much?

[Islandboy85]

This may be in the wrong place, so if it is, sorry. I am trying to find if there is a general rule of thumb for how much head space you leave in a connicle fermenter so you don't end up with a mess.
I want to build my own for doing 5, 6, and 10 gallon size final batches, so I am trying to figure out which hopper size I should buy. It seems as though most people I know locally leave about 30% head space in their fermenter, but I wasn't sure if I could get away with less.

https://www.homebrewtalk.com/f51/diy-conical-fermenter-14855/
http://www.toledometalspinning.com/products/hoppers/priceList.asp

 

[SporkD2]

it really depends on the beer recipe, yeast, and temp your fermenting at. I usually leave 1g of headspace and on most beers its ok

 

[ibrewit]

30-35% is a good rule of thumb. Each beer and yeast is different. I have had some krausens consume all of 30% headspace.

 

[Islandboy85]

Thanks guys. I guess I have another question then. Does the shape of the fermenter ie. larger diameter or tall and slender hopper affect how your fermentation will take place in your conicle?