We get asked all the time... won't my efficiency suffer....Don't I need to sparge....will I be able to brew high gravity beers....and the list goes on.
The truth of the matter is that 3 vessel system offer no (none, nada, zip) advantages over our single vessel brewing systems on a nano brew scale. When you get down to it, 3 vessel systems don't make much sense on a system under 2BBL in volume, and then it's only because removing the grain is a challenge in that large of a single vessel system.
To answer the above questions, lets start with efficiency and sparging. Most of our customers (and yours truly) get mid 80's for Mash efficiency and high 80's are not uncommon. The not so secret secret is in how we mash. We start out with all of the water for the batch in the kettle and recommend a finer milled grain (or just run it through twice). While mashing we have a continuous vortex action going on within the mash basket, recirculating from the bottom valve to the top recirculation port. By creating a whirlpool we are continuously stripping the sugars from the grain. By keeping the grain constantly moving we never have to worry about dough balls, stuck mashes, hot or cold zones etc. Our mash is always consistent. Once the mash is complete we raise the temperature to 168-170 degrees to help the final sugars release from the grains and hold for 10 minutes (while still recirculating). Once the mash is complete just raise the basket and allow it to drain while you are getting up to boil temperature. At this point you can simply remove the basket or use the rinse feature to remove the final sugars from the grain.
Compare that with a traditional 3 vessel system. With that process you have a thicker mash which can be prone to temperature differences, even if you are recirculating. At the end of your mash you sparge with 168-170 degree water for the exact same reasons that we mashout at the same temperature, to release the remaining sugars, but towards the end of your sparge most of what ends up in your kettle is colored water with no real sugar content at that point. Most small scale brewers do not monitor their wort to know when to stop collecting, they simply use whatever volume of water the recipe calls for. With single vessel brewing we eliminate the need to discard last wort.
And what about those high gravity beers? You can brew high gravity beers just as easily with a properly sized single vessel system as you can with any system.
And finally, with single vessel brewing you will be producing better beer in as little as 3.5 hours with minimal cleanup.