HERMS Tips

Over the last two years since building this brewery I've had to overcome quite a few obstacles. Things haven't always gone well and I've had moments where I've considered abandoning HERMS brewing altogether in favour of a simpler infusion system. However, eventually I have managed to work through all the issues and am completely happy with my system .

Here I'll list as many of the issues as I can remember (and some others I think might be of help) and I'll also detail how I overcame them. Most of the issues will be related to set mashes so if you experience this symptom in your system you should consider all of the remedies below. I'll try to stay away from general brewing issues concentrating on specific HERMS issues.

Symptom	Cause/Remedy
Mash temperature drops when the pump is started.	This is quite normal. It takes a while for the temperature in the mash tun to equalise. After a couple of minutes it should start to rise. Preheating the heat exchanger will help considerably.
Temperature of the mash does not match that shown on the PID.	The PID needs setting up so that the temperature of the wort exiting the return manifold matches the temperature shown on the PID. This is achieved by changing the bias/offset value.
The mash temperature never stabilises at the set value of the PID.	The PID needs to be auto-tuned every time you change the flow rate of the return. Changing the flow rate changes the system dynamics.
Noisy pump.	Air in the system. Bleed the pump. Also indicative of a set mash.
Air bubbles in the tubing.	Can be caused by or lead to Set Mash. Bleed pump and tubing from the mash tun and restart recirculation.... slowly!
Set Mash - Grain appears covered in several inches of wort.	To an extent this will always happen in a HERMS set up. It's due to the suction from the pump dragging the grain towards the manifold. However, if the mash gets too compacted the recirculation flow will stop necessitating stopping the pump, breaking up the grain bed and resting for 5 minutes before resuming recirculation. Can be caused by too high a flow rate.
Set Mash - Airlock in system	This was the biggest problem for me and took a long time to identify. An airlock in the heat exchanger was causing slow runoff which, in turn, caused the pump to suck the grain bed into the manifold resulting in a set mash. To cure this I now pump hot liquor from the HLT, through the heat exchanger and back into the HLT. Then I syphon back through the heat exchanger before connecting to the mash tun. Since adding this to my process I haven't had a set mash.
Set Mash - Slowing runoff	If the mash is only just starting to set it can sometimes be cleared by pumping from the HLT to the mash tun through the exit manifold.

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