A 5-gallon round beverage cooler is ideal for 3-gallon batches and the occasional normal gravity 5-gallon batch if you use traditional continuous sparging. One of the reasons why I quit brewing was that I found myself dumping perfectly good batches in order to be able to brew often enough to keep my yeast bank healthy. I like to be able to propagate a brewing culture whenever I subculture a slant. I could not do that when I brewed 5-gallon batches because the beer would queue up to the point where I would not have free keg space available for several months. I wound up performing a lot of slant-to-slant subculturing just to keep my thirty-plus culture bank in good shape.
I decided to limit my kegged batch size to 3-gallons when I caught the bug again last summer. I re-scaled all of my recipes to yield 3.75 end-of-boil kettle gallons and 3.5 primary gallons, which easily yields 3 full gallons of kegged clear beer. My entire brewery is designed around this batch size. I use modified 5-gallon Igloo industrial beverage coolers as my mash/lauter tun and hot liquor back (I soft-plumbed my Adventures in Homebrewing false bottom in order to make cleaning easier), a modified 27-quart Vollrath Optio 3506 stockpot as my kettle, and a Camp Chef Pro 30 as my stove (I like this stove even more than I liked my old Superb PC-100).
By the way, my first beverage cooler-based mash tun was a 10-gallon Gott (Rubbermaid). I really disliked mashing normal gravity 5-gallon batches in that cooler. I continuous sparge and there is just too much empty space in a 10-gallon cooler with a normal gravity beer. I moved to using a 7-gallon Rubbermaid beverage cooler as my mash tun in the second half of the nineties. In my humble opinion, 7-gallons is the perfect size for 5-gallon batches for people who use traditional sparging. A 7-gallon beverage cooler is large enough to handle high-gravity grists and small enough to hold temperature well through the end of the sparge when mashing normal gravity grists.
Here are a few photos of my current setup (it easily fits on a card table):
I chose to use a 27-quart Vollrath Optio 3506 stockpot as my kettle because it has a 1:1 height to diameter ratio (the stockpot is also induction ready). I went with a sanitary-welded 316 3/8" high pressure coupler (the weld cost almost as much as the stockpot), 316 close nipple, 316 ball valve, 304 hose barb, and an internal KettleValve 3/8" boil screen.
Kettle Weld
Inside the Kettle
Inside the Mash Tun
In the end, I know that 3-gallon brew houses are not for everyone. They are expensive to build compared to 5-gallon brew houses, especially when 3-gallon kegs are factored into the equation. However, for me, it was about having a brew house that was tailored to my standard production batch size. I also own an American-made Polar Ware 321BP 32-quart brew pot with false bottom for boiling the occasional 5-gallon batch. I could boil a normal gravity 5-gallon batch in my custom-built 6.75-gallon kettle, but it wouldn't be fun.
By the way, I purchased my Igloo industrial beverage coolers from Zoro Tools (the retail arm of Grainger). They are the cheapest source for this model on the Internet.
