HERMS Flowrate vs Sparge Flowrate

What is the proper flowrate for a HERMS?
I've read what appears to be conflicting information. With a HERMS, you should target ~1gal/min of flow. However, Palmer's book claims that in order to prevent compacting the grain bed during sparging, you should not exceed 1qt/min.

I mash in a 5gal round cooler with a slotted copper manifold. Is it even possible to maintain 1gal/min?

proper flow rate is as fast as you can without compacting the grain bed. on some of my beers, that means i have to limit the flow considerably. others- i can fully open the pump with no problem. depends on what grains and false bottomyou have.

the slower the flow rate, the slower the temperature change will be realized in the main mash tun. also that means the longer amount of time the wort sits in the HERMS coil being heated. if you are only trying to maintain a temperature you already reached, it doesnt have to be that fast. if you are trying to step the mash from one temperature to the next, a higher flowrate will speed this up (assuming the HERMS heater isnt the bottleneck).

Thanks.
In my last batch, I was able to maintain ~1gal/min during the mash (155F). However, as I began to mash out (~170F), the flowrate began to decrease. This occurred without any adjustment to the pump. Is it typical for the grain bed to "thicken" as the temp rises?

I'm thinking that maybe the flowrate was too high and I was compacting the grain during the mash. The flowrate might have been decreasing the whole time, but I didn't notice the slowing flowrate until the mash out.

My mash recircs at 1-2 gpm (herms or otherwise). My sparge takes around 50-60 mins to sparge 15 gals. That's a big difference.

jpietraski said:

Thanks.
Is it typical for the grain bed to "thicken" as the temp rises?

I'm thinking that maybe the flowrate was too high and I was compacting the grain during the mash.

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when grains absorb water, like white rice, they thicken, yes. however this should happen normally in the first few minutes. it doesnt take the entire mash. sounds like you got some compaction. what was your mash efficiency on that batch?

SankePankey said:

My mash recircs at 1-2 gpm (herms or otherwise). My sparge takes around 50-60 mins to sparge 15 gals. That's a big difference.

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I don't understand this. If you're pulling the wort from under the grain to recirculate, and if you have to go slowly to keep from compacting or channeling, why can you go faster why can you go faster than the sparge rate? Is there really that much difference between how fast you can sparge and how fast you can go without channeling or compacting?

audger said:

when grains absorb water, like white rice, they thicken, yes. however this should happen normally in the first few minutes. it doesnt take the entire mash. sounds like you got some compaction. what was your mash efficiency on that batch?

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This was my first batch with the HERMS.
I got ~80%.

Is there really that much difference between how fast you can sparge and how fast you can go without channeling or compacting?

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bed compaction and sugar extraction are two entirely different things. i normally sparge for around 45 min, +/-15, depending on how many lb of grain are in the tun. still perfecting my fly sparge technique...

However, Palmer's book claims that in order to prevent compacting the grain bed during sparging, you should not exceed 1qt/min.

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that number is highly dependant on the configuration of your mash tun, especially the false bottom. for me, i can go 1-2GPM and not compact the grain bed very much. that is using a 15 gal keggle and a steel mesh dome-type false bottom. not sure if a copper manifold like yours would be better or worse at compaction. 1qt/min seems low in any case though.

also- 80% is pretty good. if you can do that consistantly, i would be happy right there. remember its very rare to get over 85-90%. and no one is getting 100%. the cost difference between 70% and 80% on our scale is like $2 worth of grain, so sometimes its just easier and cheaper to adjust your grain bill for a slightly lower efficiency, then it is to go crazy chasing that extra 5%.

Thanks Audger.
I'm gonna try to brew this weekend. I'll keep an eye on the flow throughout the entire process.
I'll post the results.