Once the HERMLET concept gelled, it was hard to believe how simple the machine design is.
(Note to self - must test the idea in real life)

Description

The blue rectangle represents a single vessel (or tun), and in our case it will be a regular 20 litre stainless steel urn. We picked this up at a Trash 'n' Treasure market for about $20.

The grey rectangle labelled 'Mash Tun' is a second stainless steel container that sits inside the urn. This is a 12 litre cheap Chinese import stainless steel cooking pot. We picked ours up at the local cheap import shop for $7.50. Think of this configuration as a double boiler. When mashing, there is liquor both inside the mash tun and outside the mash tun. The outside liquor helps to keep the inside liquor warm.

The plumbing is kept as simple as possible. We intend for HERMLET to be a recirculating system because we like the temperature control we get this way. An even simpler system could be made without the pump and recirculation plumbing, but this would limit the flexibility, particularly with step mashing.

The liquor comes into the urn at the top left on our machine (simply because the urn already had a ready made hole for our plumbing). There is a single valve that allows the wort to be drained into a fermenter located at the bottom of the urn. Configure this valve as you would for a kettle drain valve.

Process

With the mash tun in place, the urn is filled with sufficient liquor to mix with the grains. This liquor is then heated to strike temperature. Grains are then poured into the mash tun and mixed with the liquor (dough-in).

Liquor is recirculated through the grains to regulate mash temperature. Liquor temperature is controlled with the urn heating element. Liquor at the bottom of the urn is pumped back into the top of the mash tun, draining slowly back through the grain, out through the false bottom and back into the urn. (The false bottom is depicted in the picture as a black arc).

Step temperature mashing is easy with this method as per HERMS and RIMS configurations.

Once the mash is complete, the mash tun is slowly lifted out of the urn and the remaining mash liquor is allowed to drain into the urn. Our machine will have some kind of gantry and winch system to allow easy lifting at this stage. The larger the brewing system, the more weight will need to be handled. Because this rig is small, we anticipate lifting no more than 6-8 kg of soggy grain.

The urn now contains wort that is diluted to the required volume and then boiled with hops added when needed.

Pros and Cons

Advantages

• The mash tun does not need to be an insulated vessel.
• The outer vessel acts as both hot liquor tun and kettle
• Only one heating source is needed
• Simpler requirements for controls
• No need to heat separate hot liquor for sparging
• Plumbing is very simple - 1 inlet, 1 outlet, 1 closed loop

Disadvantages

• Lifting the mash tun may pose problems, particularly in larger systems
• The system is (likely to be) less efficient than a three tun configuration
• Topping up the kettle with liquor prior to boil is likely to increase the time to reach boil

Other design notes

The origins of this design are manifold. There is the inspiration from the "brew in a bag" movement on the Aussie Home Brewer web site, and PistolPatch needs a special mention.

Then there is the "no chill" movement on the same web site who believe that there are many advantages to dropping hot wort into a storage container without flash chilling. As we face even tougher water restrictions in Melbourne for the summer ahead, this seems like a really good idea.

Then there are other cool inventors such as Gerd who built a most beautiful and intricate brew rig before even making any beer. He provided the inspiration to move from "brew in a bag" to this system with a mash tun inside a kettle. Gerd's brewing machine

Then there is my brew-buddy Leah, who through losing most of the function of her left arm has caused me to think about simple ways to make beer without all the heavy lifting and cleaning that comes with 50 litre kegs.

One of the features of the mash tun will be a tilt mechanism so that once it is lifted mechanically, the grains can easily be removed from the vessel as well.

Oh, and I'd like to thank my Dad who was also a keen maker - I now understand why he spent so much time in the workshop. I wish he had access to the tools and equipment that I have.

Conclusion

OK, it may be pushing things a little to claim this as a one vessel system, but it is pretty close to it. Anyway, as a maker who carries the curse of "What if I just add this extra bit of functionality/complexity...", I'm really happy to have finally designed something that in its essence is so very simple.

The proof is in the beer tasting ...

Oh, and we intend to do a "Race against the machine" brew-off between HERMAN and HERMLET when both machines are functional. S W E E E E T!

It may be mid-winter here in Melbourne, but yesterday the sun was shining, we were brewing, and mostly HERMAN did the hard work for us while we sorted out fermenters, cleaned a few bits and pieces and reflected what to do with a Belgian wheat that was over-bittered.

We were due to make our American Pale Ale last week except that we were distracted by the HERMLET project (see previous blog). But this week we loaded our wort with Cascade hops and enjoyed the sweet fragrances that brewing brings with it. This beer follows the same recipe from one a few weeks ago where we used Nelson Sauvin hops in place of the Cascade. The Lady Nelson Ale is already a hit with all in this household.

Anyway, after a few minor tweaks, HERMAN did his thing again and this time the PID control worked like a charm.

In the graph above, the dark blue line at top is the hot liquor tun oscillating gently around the set target of 80 deg C. It does not have PID control. The dark red line shows the mash temperature and heating is controlled by the PID controlled heat chamber. The red line is smooth and hits target perfectly, even though the green line still oscillates. This means the PID could still do with some minor tuning, but we are very happy with the net result.

Next weekend we will either brew a batch of Belgian wheat beer to revive our last one (which has too much bitter pith from citrus fruit in it), or we will continue work on HERMLET.