Tempurature Controlled Fridge

How to build a temperature-controlled refrigerator
by Thom Cannell

Maybe you’ve brewed in the summer and watched helplessly as fermentation temperatures soar beyond your 64° F target, or perhaps you’ve decided to make your first authentic lager. Either way, you need a temperature-controlled refrigerator. Here’s how to build your own.

Start with a refrigerator large enough to hold at least one fermentation vessel. Likely it’s an old fridge, used, abused and close to being discarded. Regardless of condition or age, if it works, it’s good enough. You’ll need this refrigerator and a precision temperature controller, available from homebrew suppliers or Grainger Corporation (www.grainger.com).

Your first consideration is the refrigerator. For information, I turned to a pal who owns an appliance store. Bill LeVeque, owner of G&W Maytag in Okemos, Michigan, has helped dozens of homebrewers convert refrigerators.   

“You need to have a cyclomatic refrigerator, not one that is self- defrosting,” says LeVeque. “The simple cyclomatic (compressor, condenser, evaporator) requires manual defrosting. A self-defrosting model will warm up every 6 to 8 hours and may rise to 55° F.” This is not too good if you’re lagering.        

The difference between refrigerator styles is easy to spot; cyclomatic refrigerators will have coils in the back. A self-defrost has coils under the refrigerator (and wires and tubes in the sides). Cyclomatic refrigerators also have flat floors suitable for fermenters. Used models, with a warranty, cost about $75; a new one is $300 or so.

If the interior walls are damaged, cracks and holes can be repaired with epoxy or RTV silicone and anything flat — like thin plywood or clear Lexan. If the door is damaged, you could fill the opening with several layers of foil-faced insulation and cover it with plywood. Just make sure the insulation is sealed into the door and that the door is mechanically stable. Bill suggests using thin luan plywood and injectable foam, like the stuff you use to insulate your home.

Another reason to modify the door is depth. My photo model’s shelving intrudes almost four inches into the refrigerator chest. Removing the shelving (look under the door gasket for mounting screws) might make room for an extra fermenter. For now, the molded shelving panel will remain.

Old refrigerators usually have a pressed aluminum box in the top. This is the freezer. If the door to the freezer compartment is missing you might want to construct one. If you will be lagering and keeping the temperature cool, you could store hops in the freezer. This would require a door. But if you’re trying to keep an ale at 67° F or a weizen at 70° F, then there would be no point because the freezer temperature will reach 55° F or more.

Another feature likely to be missing is a defrost tray. Most trays have a flapper at the rear to help control ice build-up during humid months. I removed the tray, since its five-inch height prevented using 6.5-gallon glass fermenters.            

Finally, make sure the door gasket is sealing correctly. Wash and scrub the gasket and sealing surface. If it’s stiff, Bill recommends rubbing some petroleum jelly into it to restore flexibility. Otherwise, bulk door gasket only costs a couple of bucks a foot.

Now for the shelves. My fridge came without shelves. That didn’t matter since no refrigerator shelf is the correct height for holding fermenters. The measured height of my fermenters, plus five inches for the bubbler, vary between twenty-three and twenty-six inches.

To make the refrigerator suitable for holding two or more forty-five pound fermenters, I needed a sturdy shelf at least twenty-six inches below the freezer. There was no such option. Fortunately, the refrigerator has a deep “bench” at the back where the compressor resides.    

That would provide a solid shelf support at the rear, but the defrost tray was only twenty-four inches above it. I removed the tray and used the rear bench as a support.

To find the depth of the shelf I measured in 3.5 inches, the depth of the door shelves, and made a mark (see photo). It is 11.5 inches from there to the rear bench which will be the rear support.

To make shelf rails, I used one-inch by one-inch aluminum angle brackets cut to length. They are mounted level, at the same height as the rear support, and attached with four aluminum pop rivets per rail. The shelf should be sealed and painted and secured to at least one rail. And because I’m a perfectionist, I placed a support down to the steel floor of the refrigerator. Three fermenters weigh almost 150 pounds. A milk crate with boards atop would give the same support.

Now the high-tech part, controlling temperatures. The thermostat inside a refrigerator is neither precise nor will it allow settings as high as 68° F. The answer is a precision thermostat. Some allow you to plug the refrigerator into them and control power (see page 58). Others replace the thermostat in the refrigerator. I chose a Ranco ETC 11000 from Grainger for $52.85 plus tax (Grainger #3ZP77).

Before installing the new controller, turn the existing control to maximum or “on” if you don’t want to remove it, and unplug the fridge. If it’s already defunct, as ours was, remove the thermostat and tape over any connections not in use.           

Our new controller is microprocessor-based and has setpoints from minus-30° F to 220° F. It also offers a differential adjustment of 1° to 30° F and an eight-foot temperature sensor cable.

Why is differential adjustment important? You want your beer to maintain as even a fermentation temperature as possible. And if you’ve watched your fermentations, you know that some yeast are so exothermic (heat giving), they raise the wort temperature by 7° F or more. So keeping the air inside the refrigerator constant is crucial. The Ranco ETC can accomplish this easily. It’s able to switch 16 amperes, which is more than sufficient for our modest 3.75 amp requirement.   

For installation, Ranco expects standard practices. That is to say, conduit, strain relief and proper connectors and connections. Remember: Black is hot. It goes to the brass color/narrow spade of the power connector. White is neutral. It goes to the silver color connector/wide spade on the plug. Red is traveler. It connects power.

Be sure the refrigerator is grounded: Since brewing is messy and wet and your new refrigerator is likely to be installed on a concrete floor, I would highly recommend spending $10 to $20 on replacing your power outlet with a “Ground Fault Interrupter” (GFI) outlet. A GFI detects current leakage and will immediately shut off the circuit before you get a hair-curling shock.

Only a few thermostat connections are required, yet this was still a challenge because there are several ways to accomplish the same task. I disconnected the wires (red and black) from the rear of the old thermostat and considered several different options.

I could have run wires from the controller to those existing connectors, in effect replacing the defunct thermostat with the new. That meant long wires from the controller into the cabinet. Or I could have cut the power cord and wired it into the controller. That would mean the interior light wouldn’t switch on unless the compressor was operating.

I spliced in the controller at the rear to leave power to the interior light. I spliced into the white, red and black wires and soldered the connections. Then I carefully wrapped the bare wires with two layers of electrical tape, each layer going in opposite directions. I connected our wiring to the ETC, following the included directions.

I ran the sensor cable down the wiring bundle and drilled a 1/4-inch hole through an access port built into the refrigerator (the foam-injection port.) I pushed the sensor through the hole and simply taped it to the side of the box, using a shelf channel as a guide.

Setting the ETC is very similar to setting your digital watch. Setting the differential is up to you. The ETC-equipped refrigerator switches on when the temperature gets to your desired temperature plus the differential amount. Try setting a four to five degree differential and setting the temperature one degree above the desired fermentation temperature. That should provide a useful average.

Thom Cannell is a regular contributor to Brew Your Own.