HIS HERMS TUN

by Graham Sanders

HERMS - sounds magical, and in a way it is. For an all grain CraftBrewer, it's probably the pinnacle of the ultimate brewing system. It gives such control over the brewing process, that it's very difficult to mash a bad batch of wort. However, I am ahead of myself.

What is a HERMS ?

HERMS stands for Heat Exchange Return Mash System.

The idea is simple. With most mash systems, we CraftBrewers will try to hit the right temperature with a bit of science, experience and guesswork. Rarely will we hit the exact temperature. There will be hot and cold spots, and getting an even distribution of heat is very difficult. Especially right to the bottom of the mash tun.

Further more even if you do hit the mark, the temperature will drop over time. Now to most CraftBrewers this is no real concern. These problems will have little effect on the final result. But to a small percentage of brewers, they may want a bit more control over their temperatures. This is where a HERMS comes into its own.

How does it work ?

A HERMS is nothing more than a tank of hot water that acts as a heat source. By setting the water at your target temperature, you can maintain the temperature of your mash by pumping your wort continuously through the heat exchanger that sits in this hot water.

When the mash is finished, the water in the HERMS tank is now your sparge water, so there is a great saving in heat and time. You should read my article on MY BREW DAY to understand the concept in detail and to see how the system actually works.

How to make the HERMS tank.

This is my HERMS keg setup and in place ready for my brew day.

The foam top just sits on the top, and helps traps heat. The keg sits on a two-ring burner, which has the orange gas line attached. You can see at the bottom, the stainless steel tap and tubing to take the sparge water to the mash tun below.

The plastic line is where the wort is pushed (via a pump) from the bottom of the mash tun into the HERMS keg, and the copper pipe at the top is the return back to the top of the mash.

Now lets look closer at the HERMS keg.

This is the inside of the keg. The heat exchanger is nothing more than a copper pipe, coiled. Also note the fact I have welded a short length of wider stainless steel pipe through the side. This is necessary as I found there is a bit of weight on the wall of the keg if you just insert the pipe through the wall.

This weight does make it unstable and difficult to seal. This is where the stainless pipe really works. The pipe supports the copper coil nicely. The copper coil is sealed in the stainless steel pipe by food grade sealant. A neat simple trick that is extremely strong.

Now unlike the other kegs I have, this keg is a CUB 50 litre keg. I wanted a wider keg than the narrower Lion Nathan keg as it had to fit the copper coil. I also had to cut the top clean off, otherwise I could not fit in the copper coil. Now its tricky to get it in, remember it one piece only, and you need all the room you can get to make it fit. The secret was to insert the long (exit) line first. To do that you have to put the coil upside down, and insert the longer return line first.

Once in you need to rotate it 180 degrees to get the inlet side at the bottom. You can't do this unless you totally remove the lid.

Let's now look at the bottom. This is the base.

Again like the boiler (see the Bottler of a Boiler article for more details), I have cut the rim off the base to allow plenty of air to get underneath the burner. Again, I have also inverted the base to allow more heat to be concentrated towards the centre of the keg.

Also, note the length of the exit pipes.

To better understand this how this system works you should read my Brew Day article.

Well that just about sums up my HERMS keg.

Now if you don't like gas, there is no reason you couldn't put an electric element in as a heating source instead.

A HERMS system is not that difficult to make and you will find it very rewarding. There is no set design that works. I have seen many different types and the funny thing is, they all work.

Let your imagination fly.

Shout
Graham Sanders