External HERMS Coil

I’ve been wanting to put this together for quite some time.  I’ve had the coil for a long time and the Quick Disconnects have been installed onto the hoses for about as long.  Well, now is that time.  I am going to use this HERMS coil externally because I do not want to install it into my HLT.  It will also make the system more modular to be its own entity.

For those who don’t know, a HERMS coil is used to maintain a consistent mash temperature.  It’s an acronym for Heat Exchange Recirculating Mash System.  Simply, during the Mash, you circulate the sweet wort through a pump and into the coil that is submerged in a vessel that has water at the same temperature as your target Mash temperature and then back into the Mash Tun through a sparge assembly.

Pardon the crude drawing, but here is a visual representation of the basics of HERMS.  The arrows show the direction of the sweet wort flow.

Seems pretty simple, right?  Let’s see if we can’t over-complicate it, then.  I’d roll my eyes, but it is my M.O.

First, I need to take stock of the equipment I have to make this.

Coil ✔
Kettle ✔
Pump ✔
Hoses ✔
Temperature Controller ✔
Immersion Heater ✔
3-way Valve
Mini Ball Valve

It seems that I have most everything except the 3-way Valve.  I could use the valve that I take off the Mash Tun in place of the Mini Ball Valve, but since I want to install this directly onto the outlet port of the pump, my big 3-Piece Ball Valve is too large and quite possibly too heavy.

Because I need a 3-Way Valve (well, not NEED, but want) I’ll also have to get Male Quick Disconnects for it.

I got the 3-way Valve from Amazon

1/2″ Female NPT 316 SS Type T Mounting Pad 3-Way Ball Valve with Vinyl Handle WOG1000

Keep your eye on it.  The price fluctuates between $20.99 and $23.99.  The difference is that the one for $20.99 is on a slow boat from China and the other ships Prime.

Then it was off to bargainfittings.com for the rest:


$28.43 with shipping

Once the 3-way valve showed up, I had to see how to incorporate it into my plans.  As you can see, with the center of the Tee attached to the Mash Tun, the Valve is always open no matter the position of the handle.  In the position shown below, the sweet wort would flow both directions.

So I turned the handle 180 degrees and then took it off and flipped it.

This made it so that at the center position, the solid wall of the ball in the valve is toward the Mash Tun, thereby closing the valve.  Moving the handle left or right will not control the flow in the direction I want.

Add the Quick Disconnects

And connect it to the Mash Tun

The Mini Ball Valve came in.  It’s so tiny

Here’s a size comparison next to the valve I took off the Mash Tun:

You can see why I opted for the smaller valve.  Once thing I will note is that it is not a 1/2″ flow through this valve.

Bust since the Quick Disconnects aren’t either, it shouldn’t matter.  Here’s the valve next to the QD:

Once I took the female Quick Disconnect off the pump, I removed the PTFE tape and re-taped it.  Then I screwed the new mini valve onto the pump head.

As the brewery has been expanding and changing, I have been using the inkbird ITC-308 for all my temperature controllers.  By doing this I have an STC-1000 that is no longer in use.  That makes it the perfect candidate for use in this HERMS setup.

Remember that with the STC controllers, whenever you set the temperature over 100o the third digit is the smaller font that was used as the tenth of a degree.  I have this set to 150o:

The Kettle is the same one I use for my starters and was shown in the post for Building a Yeast Bank.

The Electric Immersion Heater is the SAFE-HETE shown here.

I place the SS Coil into the pot and fill the pot with water to at least an inch above the top coil.  I then place the heater into the center of the pot and add the temperature probe from the STC-1000 into the water.

I let this heat up as my Strike water is heating, this way, the HERMS water is at Mash temp when the Mash process starts.

Once side of the coil is connected to the valve on the Mash Tun, while the other side is connected to the sparge assembly.

Once the strike water is added, I open the valve and turn on the pump, letting the sweet wort flow through the coil and back into the Mash Tun.  This process not only keeps a consistent temperature, but since the wort is recirculated through the grain bed, there is no need to vorlauf.  This process also helps to clear the wort as shown here:

Here’s the full external HERMS system in use:

I have found that this system definitely increases the efficiency of the mash by a significant amount.  I now use this for every single brew.  The last beer I brewed was Necrophiliac (Russian Imperial Stout).  It was a 15 Gallon batch and I was using a very inefficient cooler Mash Tun (120 qt).  I haven’t been able to get more than 55% efficiency from this Mash Tun in the past and have my recipe set to yield 12% ABV through this system with an O.G. of 1.118.  Using this external HERMS system, my O.G. shot up to 1.138, which when calculated against the estimated F.G. of 1.019 will skyrocket the ABV to over 18%.

I’m going to age this in an Apple Brandy Barrel for a few months.

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