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Turning an Old Refrigerator Into A Fermentation Chamber

03/07/2019

By Kieran O'Connor (Brewing Techniques)
 
An Analog Temperature Controller
 
Accurate control of fermentation temperature is closer at hand than you might think. 
 

 

You happen to be at your in-laws, nosing around their basement for some good stuff for your underfurnished apartment. What do you spy in the corner? A refrigerator that hasn’t been used since 1955. What do you do? Take that refrigerator and run!
 
Using a refrigerator is one of the best ways to minimize the number of flaws in your beers. During fermentation the internal carboy temperature can fluctuate by as much as 7 °F, altering the yeast activity and causing off-flavors. Also, the room temperature where your carboy sits can change. A refrigerator can keep your fermentation vessels at exactly the right temperature because you can set it with a thermostat. In addition to limiting flaws, refrigerators allow you to lager beers. 
 
 

First, The Fridge

 
The first thing to do is get a refrigerator or freezer. I got mine from my in-laws, but you can find ads for refrigerators in your local pennysaver publication almost any week. I wouldn’t expect to pay more than $ 50. Look for one that has the compressor located underneath the unit. If the inside of the fridge is a nice rectangular box, with no notch at the bottom back part, the compressor is underneath. The notch takes away valuable space. Bottom-mounted compressors allow you to fit more carboys in the fridge (my fridge holds two 7-gal carboys or four Cornelius kegs). Most older refrigerators have a bottom-mounted compressor. If you get a freezer, you probably won’t have to worry about this.
 

Thermostats

 
Once you have the fridge, you need a way to set the internal temperature to a specific temperature, which cannot be done using the refrigerator’s dial thermostat. The fridge’s thermostat responses generally fluctuate, so I suggest buying an after-market thermostat. Which one you buy, however, depends on what you want to do.
 
The first type of thermostat is the thermostat used to set the temperatures for room air conditioners. The monitor plugs into a simple wall outlet, the refrigerator plugs into the monitor, and the monitor’s sensing probe goes inside the fridge. After setting the temperature on the energy monitor, the probe senses the refrigerator’s temperature and turns the power off and on. You must make sure that the refrigerator’s internal thermostat is on the coldest setting, usually “10” on the dial; otherwise it may shut the fridge off prematurely.
 
One example of such a thermostat is the Hunter Energy Monitor (Hunter Fan Co., Memphis, Tennessee). The drawback of this unit is that its low-end temperature is only 40 °F (4.5 °C); if you want to lager at 32 °F (0 °C), this thermostat will not work for you. If you just plan on making ales, then go for it.
 
Another way to go is to get a device called the Controller (Johnson Controls, Syracuse, New York; William’s Brewing has an exclusive distributorship). It works the same way, but it has a wider temperature range. It goes from 20 °F (–6.5 °C) to 80 °F (26.5 °C). You can use this device for lagering, but you pay for the privilege: $ 49 plus shipping and handling. 
 
A third way to go is to buy a Honeywell (Minneapolis, Minnesota) model T-603 1A-1029. Its temperature range is 30–90 °F (–1–32 °C). It costs less than the Controller — $ 28 — but it comes with no power cord. My guess is that it would cost you about $ 10–15 to buy the wiring and turn the unit into the equivalent of the Controller.
 
Before you determine which thermostat is most appropriate for your needs, you need to do some experimenting on your fridge first. The following discussion does not apply to brewers who use freezers. 
 

How Cold is Your Fridge?

 
If you want to lager, you have to make sure that your fridge will get down to 32 °F (0 °C). It won’t do you much good if you buy the Controller and your fridge can only go to 40 °F (4.5 °C). You’ll just be wasting money. I recommend performing a few tests.
 
First, snag an indoor-outdoor thermometer (the kind with a probe), and put the probe inside your fridge. I recommend using a probe-based indoor-outdoor thermometer because opening and closing the fridge will quickly change the inside temperature. Set the fridge to the coldest setting on the internal thermostat, usually “10.” Wait about 35–40 min and see how cold it gets. If it gets to 32 °F or below, you’re all set. You can buy either type of external thermostat.
 
The lowest temperature that the fridge reaches with a thermostat, however, is not necessarily the lowest temperature that the fridge can reach.
 
Unplug the fridge and take out the thermostat. There should be two black wires inside the thermostat. Connecting them manually bypasses the fridge’s thermostat, allowing the fridge to run all the time. Connect them, and then plug in the refrigerator. Wait 30–45 min and see how low the temperature goes. My fridge went from 38 °F (3.5 °C) with the thermostat to 30 °F (–1 °C) without it.
 
Because refrigerator thermostats are designed to keep food from freezing, your refrigerator will not normally allow 32 °F temperatures. By removing it and replacing it with an external thermostat, however, you can allow this possibility.
 
Important: Don’t run the fridge without a thermostat (except for a short time), because the compressor will eventually burn out. It cannot run forever, and that’s what the fridge will try to do without a thermostat. 
 

Before You Start

 
First, if you don’t plan on using the freezer (and if it’s inside the fridge), remove the freezer door. The coldness from the freezer will keep the fridge from running as much and will keep your electric bill down.
 
Thoroughly clean the refrigerator with bleach solution. At 60 °F (15.5 C) (ale fermentation temperatures), lots of nasties will be crawling around the fridge. Kill ’em.
 
Clean the grille on the back of the fridge with a vacuum. The grille disperses the heat extracted from the inside. A clean grille will allow the heat to dissipate more quickly.
 
Depending on the size of your fridge, you could build a shelf to raise the carboys, allowing you to store or condition bottles underneath. You can also use door shelves if available.
 
If you have a freezer with built-in shelves, do not try to remove them. They have freon in them, and if they break the repairs will be costly. If shelf height is a concern, you might try using Cornelius 
kegs to store your beer for lagering. You can put the kegs on their sides; it works just fine. 
 

Energy Consumption

 
I had a device that measured electricity usage, and I slapped it on my fridge. At 45 °F (7 °C) and at $ 0.089/kWh, my fridge cost me $ 0.10/day. Obviously, your mileage may vary, depending on room temperature and the efficiency of your fridge.
 

Better Brewing!

 
If you can swing it, I highly recommend using a refrigerator for controlling fermentation temperatures. In addition to providing more even temperature for ale fermentation, it enables true lagering at low temperatures. And it doesn’t have to be expensive. 

 

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