Build a Fermentation Temperature Control System
Whether the topic is brewing techniques or DIY projects, learning and sharing with others have played a huge role in my homebrewing hobby. A common problem that I’ve found a lot of homebrewers have (this included myself) is how to keep beer fermenting at a consistent, desired temperature.
My first solution to this problem was to use a mini-fridge, which worked pretty well when I was brewing 5-gallon (19-L) batches. However, it didn’t take long before I started brewing 10–15 gallon (38–67 L) batches and didn’t have space in my mini-fridge anymore.
Now, I found myself faced with the same problem. I could simply buy a secondary mini-fridge, or perhaps a larger refrigerator that could hold multiple fermenters. But multiple refrigerators would add up in cost (not to mention the added space requirements), and while a larger refrigerator would work well if all my beers where supposed to ferment at the same temperature, it would not work if I had multiple batches that needed to ferment at different temperatures. What if I wanted to make an Oktoberfest and an oatmeal stout at the same time?
This lead me looking for a solution that doesn’t take up as much space, is reasonably priced, and allows for different temperatures if needed. After spending time searching the internet and talking with friends from local homebrewing clubs, I built a fermentation controlled system.
This system is pretty simple to build and I’ve found it works very well. There are two different parts to this project — one that will heat up your fermenter and another that will cool it if the temperature rises too high. The driving force to provide the cooling effect is an ice bath. A temperature controller connected to a pond pump will turn on a pump sitting inside the ice bath to carry water through a fermentation jacket when the temperature rises too high. The same temperature controller will turn on a fermentation heater when the temperature drops too low, raising the temperature back into the pre-set range through the use of flex watt tape.
I later substituted the ice/water bath with a window air conditioning unit using its evaporating coils to cool a glycol/water solution. You can find several resources online if you’re interested in pursuing the window air conditioner option, but I’m going to keep this project simple so anyone can do it with minimal safety concerns that may arise when modifying air conditioning units. To keep the system heated I am using flex watt heat tape, however you could use a pre-made fermentation heat wrap from a homebrew supply shop and use only the cooling side of this system if you choose.
Start Your Project
PARTS & TOOLS
• Cool Zone Cooling Jacket (Gotta-Brew SKU#CJ5065)
• Flex watt heat tape (11 x 24 inches/28 x 61 cm)
• Clip sets for heat tape
• Flex watt cord set (6 foot/1.8 m, 18 gauge cord)
• Dual stage temperature controller
• Insulated cooler
• Crimping tool
• Pond pump
Step by Step
1. FERMENTATION HEATER
The 11-inch (28-cm) flex watt heat tape is 20 watts per foot. I used 24 inches (61 cm) of it when making mine. When cutting the heating element ensure you only cut through the dashed “cut here” lines.
To finish the fermentation heater, simply attach the extension cord to the flex watt. Insert each wire into the barrel section of the connector, using the crimping tool to keep the wires in place. After the wires are tightly secured, crimp the flat piece of the connector onto the silver bar of the flex watt, making sure the teeth bite down. This step will be finished after you snap the clear insulator around the connector.
2. ICE/WATER RESERVOIR
For my reservoir I chose to use a 10-gallon (38-L) cooler, which I have found to be large enough to cool four carboys at once. Replacing the spigot with a three-piece ball valve was the only modification done to my cooler. This step wasn’t necessary but I found it allowed me to drain the cooler of water quicker when adding fresh ice.
Holes can be added to the lid with a 7⁄8-inch step drill bit to allow the vinyl tubing from the cooling jackets to go into the cooler. Simply placing the lid on top of the vinyl tubing is another option that I’ve found works well, and doesn’t require any holes to be drilled. These coolers also make great mash tuns and you may not want to compromise your existing equipment while trying this project. Although, securely fastening the lid helps insulate the cooler from outside temperatures and keep the vinyl tubing in place.
3. COOLING JACKETS
Instead of building my own cooling jackets out of copper coils, I decided to purchase pre-made jackets from Cool Zone. These jackets can handle pressure up to 8 PSI and fit perfectly around 5- and 6-gallon (19- and 23-L) carboys. There will be two 1⁄4-inch pieces of tubing coming out of the jackets. One will be used to carry water into the jacket from the water reservoir. The other returns the water back into the reservoir after being circulated around the jacket.
4. PUMPS
To carry water through the jacket I used a pond pump. The pump is connected to a 1⁄2-inch piece of vinyl tubing through a 1⁄2-inch outlet on top of the pump. A quick connect that came with the jacket is connected to the opposite side of the vinyl tube. I’ve used both 317 GPH (gallons-per-hour) and a more powerful 500 GPH pond pump and found using the 317 GPH pump works just as well.
5. TEMPERATURE CONTROLLERS
You’ll need to use a dual stage temperature controller in order to run both the fermentation heater and the pond pump. There are a few options you have for this. I’ve had luck using an InkBird and an STC-1000. Both controllers allow you to set a temperature and a differential. The controller will use the differential to know when to turn on your outlets. For example, if I set the controller temperature to 68 °F (20 °C) with a 1 °F (0.5 °C) differential, the cooling pumps will turn on by the temperature controller if the temperature probe goes above 69 °F (20.5 °C), and the heat source will kick on if the temperature drops below 67 °F (19.5 °C).
Your controller should have two outlets. One will be marked for cooling and the other for a heat source. You’ll want to plug the pond pump into the cooling outlet and the fermentation heater into the heat side.
My temperature probe sits inside a thermowell placed inside my carboy.
6. TEST IT
To run or test the system you’ll first want to wrap the fermentation heater around the carboy. I generally use a piece of electrical tape to ensure it doesn’t move. After plugging the heater into the heat side of the temperature controller you’re ready to put on the cooling jacket. These jackets easily wrap around the fermenter and have Velcro to secure themselves in place. Now, you’ll need to attach the pump to the jacket. I have the second quick connect attached to the 1⁄2-inch tube running back into the cooler. Each jacket from Cool Zone comes with two quick connects to make this assembly easy.
Once everything is in place you’re ready to fill the cooler with an ice water mix and set your desired temperature on the controllers. Make sure enough water is added in the cooler to prevent the pond pump from running dry. When filling my 10-gallon (38-L) cooler I use an 80:20 ice to water mix. In my experience, with this much ice the cooler will keep cold enough to be effective for about two days depending on the ambient room temperature.
