Introduction: Converting a Fridge for Fermenting Beer

Home brewing is a fun and exciting way to make your own beer, the way you like it.  The fermentation process is very temperature sensitive, and off flavors are easily developed if temperatures change by just a few degrees.  Some home brewers are lucky enough to live in a climate that enables them to use a closet or basement to keep the fermenting beer at the correct temperature.  For the rest of us, precise temperature control can be quite difficult.  This instructable will show how I used an old refrigerator and a temperature controller to keep my fermenting beer happy even in the hot sonoran desert.

Step 1: Finding the Fridge or Freezer

Either a fridge or freezer will work, and they both have their own advantages and disadvantages.  You need to make sure that your fermenter or fermenters will fit inside, and that it cools.  It doesn't matter if the thermostat doesn't function properly, as it can be bypassed.  The first item I found was a stand up freezer listed for free.  Upon inspection, I found that is was not frost free, meaning the cooling coils ran through the shelves, which means they can't be removed to make room for the fermenters.  Make sure to look for a frost free frezer if it's an upright model.  Chest freezers work very well, but can be harder to find.  They have the advantage of keeping constant temperature better when you need to open the door, and most often don't need any modifications other than adding a temperature controller.  A regular refrigerator also works well, and the freezer portion can be used to store hops, cold mugs, and other items.  

I didn't want to spend much money, and because of it's unique use, I could live with a lot of problems that might reduce the price.  I kept checking Craigslist until I found the prefect thing.  It was very dirty inside and out, missing the decorative plastic grill on the bottom, had a broken shelf support, was missing the crisper drawers, and was only $20.  Since it was going to live in my workshop, I didn't care much how it looked, and I'm happy to do a little cleaning to save some money.  I also didn't care about the shelf or drawer issues, as I planned on removing them.

Step 2: Cleaning and Stripping It

After getting it home, I removed and discarded the remaining shelves, and the drawer guide brackets.  Then it recieved a good cleaning, making especially sure to clean the rubber seal on the door, and the area where the seal contacts the fridge.  This ensures a good seal and helps reduce the loss of cold air, making it run more efficiently.  If the rubber feels old and hard, rubbing some petroleum jelly into it will restore it's softness and flexibility.

Step 3: The Shelf

The bottom of most refrigerators have a hump, or angled back to accomadate the compressor.  Wanting to maximize the useable space to fit as many fermenters as possible, I wanted a shelf to raise them above this hump.  After some measurements, I realized that if I left 24" of room above the shelf, I would have enough space for my fermenters with an airlock or blow-off attatched, and still have room to bottle condition tall 22oz bottles below.  I cut a scrap piece of 3/4" OSB to the correct size.  I used OSB simply because it was what I had available in my scrap pile.  Next I determined the length of the legs, and cut them out of some 2X scrap wood.  I then determined where the rear legs would need to sit so that they didn't interfere with the angled part at the back.  After marking the leg locations, I screwed them in place, and then screwed the front legs on to the very front.  I oriented the legs to give the maximum amount of access to the bottom shelf.  When I tried to install the shelf, i found that the shelf supports for the very bottom shelf were in the way.  A quick tap with a hammer broke the brittle plastic, and allowed the shelf to slide in place.

Step 4: The Door

The plastic door panel had molded shelves that stuck into the fridge area, and only allowed room for 2 fermenters.  I figured that if I were to replace the molded plastic with a flat panel, I would be able to fit at least 3 and maybe even 4 fermenters.  I wanted something flat and fairly thin so that I could re-use the same rubber door seal.  I considered using dry erase board which would allow me to keep notes about the beer fermenting, but the cheapest one I could find that was large enough was $25, and a sheet of 1/8" hardboard is only $6.  I ended up settling on hardboard coated in white melamine (about $8), thinking I might be able to use crayons to keep notes on it. 

The first step was to remove the door from the fridge.  This is usually pretty straight forward, and in my case just required removing a few screws from the hinge pin holders.  Then I lay the door face down on a flat work surface with the handle overhanging the edge.  This is important, because otherwise the door will warp from it's own weight after the panel is removed, and the new panel will hold the door in the warped contour.  If the workspace doesn't allow the door to lay flat, you may need to remove the handle.

The next step was to remove the molded panel.  It was held on by sheet metal screws hidden underneath the rubber seal.  I folded the rubber back, and removed the screws, making sure to save them.  The screws actually held down metal strips, which in turn held the rubber in place.  I took note of the orientation of these strips, as they wanted to fall out as I moved the seal away from the door.

Next I measured the outside dimensions of the panel, and cut the hardboard to size.  I placed the shelf panel on top of the flat panel, and used it as a template to mark the locations of the screw holes. 

Step 5: Installing the New Door Panel

With all of the screw holes accurately marked, I drilled all of the holes slightly larger than the screws.  With all of the holes drilled, I placed it on top of the door, and checked the hole alignment.  I used the drill to slightly enlarge any holes that didn't line up perfectly.  When it all looked in line, I placed the rubber seal and metal strips in place.  I carefully held everything in place while peeling the rubber back to expose the hole, and started in the centers and worked my way to the corners.  I found it easier if I didn't tighten the screws completely until they were all in place.

After the seal and new door panel were on, I re-installed the door onto the fridge.  A quick check confrimed that I would now be able to fit 4 fermenters and two one gallon growlers  on top of the shelf, essentially doubling the capacity.

Many fridges rely on the door panel to push a switch to control the light.  I used this to my advantage to check the seal of the door, by turning the fridge on, the shop lights off, and checking all sides of the door for any light leaking out.  Afterwards, I temporarily taped the switch down so that the light stays off all the time.  I may attatch a small block to the door that will activate the switch if the lack of light becomes a problem.

A couple of days after putting my door back on, I realized that the door had a good seal most of the time, but would shift slightly if the door were leaned on, and the seal would no longer be as good.   After a little messing around, I discovered that the bottom hinge pin hole in the door had become elongated over time, allowing the door to shift slightly.  I realized that I could switch the swing of the door to solve this issue.  I had to remove both the fridge and freezer doors in order to switch the handles and hinges to the other sides.  As an added bonus, the new door swing is actually a little more ergonomic for the location I chose for it in my shop.

Step 6: Adding a Temperature Controller

The easiest method of controlling the temperature is to buy an external programable thermostat.   If the fridge has a thermostat, you will want to set it to it's coldest settings so that the external thermostat controls everything. 

I use a digital Ranco controller, which works great, but is only single stage, meaning that it can control either heating or cooling, but not both at the same time.  It rarely gets super hot during the day and then super cold the same night here, so it hasn't been much of an issue.  The thermal mass of 15-20 gallons of beer is usually enough to even out most fluctuations.  The nice thing about it is that is's essentially plug and play.  I may replace it with a dual stage controller like I have on my kegerator, which will require a little wiring, but should make operation a little more convenient. 

In either case, it's a good idea to tape the temperature probe to the fermenter, so that the sensor is reading the beer temperature instead of the ambient air temperature inside of the fridge.  It also helps to tape a piece of foam or other insulation on top of the sensor.  If the probe is water proof, it can also be permanently mounted in a small vessel filled with liquid instead of attatching it to the fermenter.

Step 7: Heating

During the warmer months when the ambient temperature is higher than the desired fermentation temperature, the fridge will do the cooling.  During the colder months I need some way to heat the chamber.  I used a cheap $1 ceramic light fixture, and mounted it on a scrap of 3/4" MDF.  I siliconed all the seams to make it as water tight as possible, and then made some feet to lift it off the bottom surface using screws.  This is just in case I have an overflowing fermenter or exploding bottle.  I then bought a ceramic infrared light bulb from a pet store.  They're normally used to heat terrariums for snakes and lizards.  When temperatures drop, I simply place the heat bulb under the shelf, and then plug it into my temperature controller.  The only disadvantage is that I can't fit as many bottles under the shelf to bottle condition during the colder months.