Brewhouse Efficiency 5.5 gal batches on a 10 gal system

[Vintage63]

I use a 10 gallon HERMS More Beer sculpture with 15 gallon kettles. In the boil kettle, I use a curved diverter to pull wort from the side of the kettle rather than the middle when transferring to either a 6 or 6.5 gallon glass fermenter. I also use a counter flow chiller.

I like the flexibility to brew both 5.5 and 10.5 or 11 gallon batches depending on how much of a particular beer I want to keep around or if I want to split batches. I generally find myself brewing more 5.5 gallon batches though since getting the sculpture.

I use the latest version of BeerSmith to manage recipes and my process.

The problem is I cannot dial in a consistent efficiency number for 5.5 gallon batches (11 gallon batches is pretty consistent at approximately 79%). I understand the percentage will drop when doing smaller batches in a larger mash tun than the system is designed for, but holy crap I can't figure it out.

For a 5.5 gallon batch, I have ranged from 61% to 69% but it now seems to be hovering at approximately 62%. I am using 1.6 qts/lb water and fly sparging with a float switch, shooting to always have about 1" of water on top of the grain bed. I've plugged all my losses into the software (mash tun dead space, remaining wort, trub, hoses and counter flow chiller).

I am really hoping to learn more about really why this happens and any tips to help keep it consistent.

Thanks for any help/feedback out there on this subject.

 

[skunkfunk]

That's pretty odd. Different boil parameters? Have you tried a variable mash water / grain ratio such that you collect 50% from first runnings and 50% from sparge runnings? Maybe just try a no-sparge (full volume mash) and see if you still get the same efficiency? Have you considered putting the grain in a bag so you can get at the dead space? I dunno, never had a 10 gallon system so I'm kind of grasping for straws here.

 

[Vintage63]

Thanks skunk. The only thing I have tried is increasing the water to grain ratio. I am now at 1.6 qts per gallon. I've been reluctant to go much higher because of thinning out the mash. No sparge seems interesting.