Author Topic: HERMS and stuck mash  (Read 1531 times)

Offline hike20

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HERMS and stuck mash
« on: October 27, 2014, 05:02:38 PM »
I do small batch (2.5 gallon) brewing and recently upgraded to a HERMS setup to improve my mash temp stability. I use a 5 gallon round beverage cooler for my mash tun, with a 9" domed false bottom. I circulate with a chugger pump through a 1/2" immersion coil that I also use for chilling the wort.

My problem is that the mash becomes stuck within a minute or two of recirculating. I've tried cutting back the flow from the pump as much as possible but it still sticks. I've tried adding rice hulls (generally around 1/4 to 1/2 lb for 5-6 lbs of grain which seems like a lot) and it helps some but I still have to watch it like a hawk and it takes a lot of patience to get it flowing well.

I've tried different mash thickness as well, from 1.25 qt/lb up to around 1.75 qt/lb. It doesn't make a difference. The issue seems to be the grain bed compacts like concrete no matter how much water is in there.

Here's what my false bottom looks like:
http://www.biyhomebrewsupply.com/collections/equipment/products/9falsebottom.

Do I need a different type of FB? If so, what do you recommend? Other ideas?

Thanks!
Randy Carris

Offline Stevie

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Re: HERMS and stuck mash
« Reply #1 on: October 27, 2014, 05:13:46 PM »
Sounds like you need a a grant. The mash drains into the grant and the pump pulls from the grant. The idea is to avoid suction on the mash bed.

Noted in this article. https://byo.com/stories/issue/item/1325-rims-and-herms-brewing-advanced-homebrewing

Can be something as simple as a small bucket with a valve at the bottoms

Offline jeffy

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Re: HERMS and stuck mash
« Reply #2 on: October 27, 2014, 10:46:29 PM »
You mentioned cutting flow from the pump.  You should have the flow restricted after the pump, not before.
Jeff Gladish, Tampa (989.3, 175.1 Apparent Rennarian)
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Offline hopfenundmalz

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Re: HERMS and stuck mash
« Reply #3 on: October 27, 2014, 11:01:35 PM »
As Jeff says, have a ball valve on the pump output to throttle the flow. It is sometimes a good idea to close the valve, start the pump, and slowly open until you have flow (not full flow). Then turn on the heating element, and see if you can maintain flow.

Another issue is that the false bottom could be bottoming out under pressure. What that means is that the elbow contacts the bottom of the tun, shutting off flow. Some designs have castellated ends so that the flow is not shut off, some guys cross drill to give more flow area. Some coolers have a small dome in the center, which makes it worse - don't ask me how I know this.

It is generally thought that slots are better than holes. On a pro level there are many examples of slots, but there are some that have holes.
« Last Edit: October 27, 2014, 11:04:53 PM by hopfenundmalz »
Jeff Rankert
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Home-brewing, not just a hobby, it is a lifestyle!

Offline hike20

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Re: HERMS and stuck mash
« Reply #4 on: October 28, 2014, 03:53:47 PM »
Just to clarify, the ball valve on the pump IS on the outflow, not the inlet. I run the valve on the tun wide open while recirculating.

The bottom of the cooler is flat to convex. I don't think the FB is flexing at all as it's very rigid. Seems like it can support way more than the weight of what I have in there with wet grain and water. There is, however, a very small bump in the center of the cooler bottom. I guess it's possible the there's just not enough clearance for unrestricted flow. I'm going to try and find a thinner nut or grind some grooves into the one I have to create channels.

If that doesn't work I'll try the grant idea. My reservation against that is more temperature loss and having another item to clean (Yea!).

Offline Stevie

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Re: HERMS and stuck mash
« Reply #5 on: October 28, 2014, 04:19:17 PM »
A grant does not need to be very big to work. A guy in one of my clubs has a tall 1 or 2 quart stainless container that functions as his grant. If kept small, I doubt the heat loss would be very much.

Offline hopfenundmalz

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Re: HERMS and stuck mash
« Reply #6 on: October 28, 2014, 05:11:53 PM »
The suction from the pump, even when throttled, can result in an appreciable force when multiplied by the false bottom area. You void even be causing the bottom of the cooler to deform up. A castelated nut on the bottom should help maintain flow.
Jeff Rankert
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Home-brewing, not just a hobby, it is a lifestyle!

Offline hike20

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Re: HERMS and stuck mash
« Reply #7 on: October 28, 2014, 10:34:24 PM »
The suction from the pump, even when throttled, can result in an appreciable force when multiplied by the false bottom area. You void even be causing the bottom of the cooler to deform up. A castelated nut on the bottom should help maintain flow.

Is there much chance the local hardware store will have a castellated/slotted nut of the right type (1/2" NPS)? Do you think it would be adequate to make cuts with my dremel tool cutting disks or will they be too thin?

Offline hopfenundmalz

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Re: HERMS and stuck mash
« Reply #8 on: October 29, 2014, 06:39:52 PM »
The suction from the pump, even when throttled, can result in an appreciable force when multiplied by the false bottom area. You void even be causing the bottom of the cooler to deform up. A castelated nut on the bottom should help maintain flow.

Is there much chance the local hardware store will have a castellated/slotted nut of the right type (1/2" NPS)? Do you think it would be adequate to make cuts with my dremel tool cutting disks or will they be too thin?

You might phone them and ask.

Looking at the picture, it might be worth a try to loosen the jamb nut on top, back the elbow out a couple of guns, then tighten the jamb nut. That shoul give clearance so it is worth a try.
Jeff Rankert
Ann Arbor Brewers Guild
AHA Governing Committee
BJCP National
Home-brewing, not just a hobby, it is a lifestyle!