guesstimating flow rate when recirculating using sight gauge? - Beer, Wine, Mead, & Cider Brewing Discussion Community.

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Well-Known Member
Nov 8, 2014
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Houston Tx
I have been doing some pretty big 10 gallon batches lately and notice that when pumping and recirculating I was getting "stuck" like sparges. I use Blichmann G2 15 Gal mash tun and realized I was at the top of capacity for considering my grain bill and grist to liquor ratio. I picked up on here that the sight gauge can be used to monitor a stuck sparge. Checked the instructions and sure enough if your gauge falls below half your volume your headed for a stuck sparge. So I started playing with recirculating volumes if you will. I noticed that you can really dial in the volume level.

So I was curious as to what level GPM is best to recirculate without compacting the grain bed too much but still give me a good recirculating rate. I noticed the G2 instructions mentioned something like 1 GPM for rims. I don't have a rims (yet) and currently direct fire under mash to keep temps constant so I need a good flow when firing.

And the second question is can I get a good guestimate on flow rate using the sight glass? IE if my starting volume shows 10G and I recirculate at a steady reading of 9 G am I at a 1 GPM flow? Seems like that would be too simplistic and doesn't take into account the time factor. Anyone have any ideas?


Well-Known Member
Dec 6, 2014
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The blichmann false bottom is really solid gear. I'd look at your grain crush or add some rice hulls if your consistently getting a stuck mash. Perhaps your just pumping to fast now because your afraid of scorching the mash?

A few degree drop in mash temp would be more acceptable to me than the risk of a scorched mash. You can turn down your burner a bit and lower your flow rate.

That said I'm not sure you can use the sight glass as an indication of flow rate. As the mash settles it will be less porous and may pull the sight glass level down but your flow rate would be the same. At that point your just pulling the bed down and compacting it faster.

Blichmann does sell their flow rate meter. I think it's $125 or more. I never could justify the cost though.

I guess what I'm saying is the sight glass level be somewhat variable relative to flow rate over time during the mash.

I have been using the sight glass as an indicator of a stuck mash for years now. I restrict my flow until I see the level remain constant. If it does begin to compact I turn off the pump and stir the top half of the mash. Then I give it a few min to settle and resume recirculating.


Moderna Or Bust! :D
May 31, 2011
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Stow, MA
Might have been one of my posts where I had the revelation that the sight gauge on my 20g G1 MLT was actually trying to keep me out of trouble ;)

fwiw, once the grain bed is set I can usually maintain between 2-3 gallons per minute recirculation rate.
But, assuming an unchanged mill gap across all recipes, there are still dependencies on bed depth, mash thickness and grain bill.
Which actually makes the sight gauge that much more useful, otherwise one could just mark their pump output throttle position and use the same setting for all batches.

I just trust the gauge and set my recirculation rate so the level doesn't crater...


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