mash conversion issues with high end of sparge gravities

[skelley]

I was hoping I could get some additional insight into a problem I am having and some ideas on how to solve it.
I am currently brewing on a stout 7bbl system with HERMS coil and a 10bbl mash ton without rakes.
My problem is that my efficiencies are too low. In the low 70's. If that was all then I could adjust but the problem lies in how it is occuring given the intermittent brix readings I am getting throughout the brew process.
My final gravity readings at then end of fly sparge are around a brix of 9 to 10. Way too high. My first wort gravities are too low and about 91% when compared to expected gravities based on a 1.5quarts/gallon grist composition. This is occuring on all big beers (17 to 22 brix beers)
My mash pH is always in the 5.4 to 5.45 range. Things I have tried so far is as follows:
-Mashing in with grain first and filling from below slowly with vigorous stir.
-Adding in restir approximately 45 minutes into the mash
-all mashes for at least 1.5 hours
I believe I am getting continous conversion of my mash apon sparging. Do others agree? I have not played with mill yet but am using a Jimboney mill with gap setting around .047-.048 as it came to me after purchase.
Does anyone else experience this? Am I left with only one option and that is to adjust mill to narrower gap?
Thanks for any input others have.

[Jonny Frazier]

Hey Skelley,

One thing I would check is that my sparge volume calculations are correct for the grain weight based on your desired pre-boil volume. If you have a lot of water left in the mash tun after sparging this could be watering down your wort. I have developed a set of constants for grain absorption rates that usually get me really close on my strike in and sparge volumes. It's basically just a function of grain weight, grain absorption rate, desired pre-boil volume(based on your average boil off rate per hour) and desired mash thickness.

Adjusting the mill is an option but just be careful not to go too far. As long as the endosperm of the grain is exposed you should be fine.

Your pH is solid so it's a hospitable environment for starch conversion. Also try to keep from compacting your grain bed when using your HERMS coil. This can affect conversion efficiency by creating an impermeable layer in your grain bed. Slow down your recirculation flow rate.

Maybe check the validity of your refractometer reading against another gage. Preferably a manual calibrated gage like a hydrometer. Could be variance in your measurement system.

Trying to think of things I've ran into. Been brewing with a smaller HERMS system for years.

Hope you figured it out already since its been a while. If you have I'd be really interested to know what you've learned. I am also interested in how efficient the HERMS system is on a larger scale. Like degrees temperature rise per minute or how long raising the temperature in a step mash takes.

Good luck, cheers!