Good fermentation has one of the largest impacts on the quality of ones beer. Of the many fermentation variables (length of fermentation time, number of yeast pitched, wort oxygenation, etc), temperature has one of the greatest effects on the final taste of beer. Fermentation chambers, which keep fermentation temperatures constant based on the yeast strain in use, can greatly improve the quality (and drinkability) of beer. In my opinion, temperature control, along with proper yeast pitch, is a defining characteristic between clean and outstanding home-brews, and ones that are drinkable. And, if you want to brew a lager, a fermentation chamber is a must.
I have a chest freezer that I’ve been using for a fermentation chamber for some time now, but it is small and has a shelf in the bottom which only gives me room for one carboy/brew bucket with a blowoff tube (not enough clearance for a air lock). Applying a collar, similar to what I did with my keezer build, I build a fermentation chamber which will fit two carboys/buckets, and it took me less than a few hours. Keep in mind, the keezer was meant to look nice as folks pour themselves a pint. The fermentation chamber sits in an unfinished part of my basement and I have no need to dress it up. I was already using a Ranco temperature controller, which I also use on my keezer.
I started by removing the lid to the freezer by removing the bottom screws. I measured the height a carboy would need, along with an airlock, from the highest point inside the freezer (a shelf inside) and determined that I needed at least 8 inches of clearance above the existing opening. I picked up a long 2×10 from Home Depot, and used screws and wood glue I had on hand. Keeping in mind that 10 extra inches makes this a deep chamber to lift and lower full carboys in, I wanted to make the collar removable so that I could easily take it off and on so I didn’t have to reach as far down.
I measured the opening to ensure the outsides of each piece of wood rested on top of the freezer opening, then I cut the boards to length, and used butt joints with wood glue and screws to square up and secure the collar. Of course, I dry fitted the pieces to the top of the freezer first, which resulted in a few pieces being trimmed a bit for a good fit.
After setting the collar on the freezer, I screwed the freezer top into the collar using the existing screws.
At that point, it looked pretty good, but was not secure on the freezer. While my keezer build involved a permanent collar, I did not want a permanent collar on this build and wanted to be able to remove it when necessary to reach deep into the freezer. I used three pieces of MDF I had sitting around, cut at about 10 inches each, which I screwed into the sides and back of the collar (while hanging below the collar over the freezer base) to mold it around the freezer. Because I had a lot of exposed wood with no insulation, I used window/door caulk around the edges of the wood to seal those openings, and then used Reflectix, which I had sitting around from another project, to insulate around the wood.
Now that this is built, I am able to add a lager I recently brewed (recipe will be forthcoming), along with aging my Westvleteren xii clone.