“Smart” Fermentation: A chamber with a CO₂ harvesting system

I started brewing one year ago and enjoy doing small 3.25-gal. (12-L) batches, as it allows more experimentation. Moreover, a 3.25-gal. (12-L) bucket is small enough to fit into my fridge for the cold-crashing phase at the end of fermentation. Nonetheless, after a few batches my flat mates were understandably not too comfortable keeping my “beer stuff” in the fridge for a whole week. My fermenter is indeed pretty small, but it still occupies a large portion of the fridge. Hence, I had to find another way to cold crash. I took up the handcrafting/technological challenge of building my own remotely monitored and controlled fridge with an autonomous system for controlling the temperature.

My fermenting chamber consists of a 3.1-in. (8-cm) thick box in polystyrene made waterproof by an inner acrylic Plexiglas® coating. Inside the box the fermentation bucket is plunged in a water bath, with water and beer volumes approximately equal. The box’s size has to be adapted to the fermenter, which in my case fits in a 13.4-in. (34-cm) cube. Adding the 3.1-in. (8-cm) of polystyrene on each side gives the final cubic box a 20-in. (50-cm) long exterior.

The temperature sensor is placed in a test tube and insulated with silicon sealant. The purpose of the test tube is to protect the sensor from moisture, and is extremely simple to clean. The cooling system consists of a small pump that forces the water to flow through a Peltier water chilling system, both the pump and the Peltier system are powered by a 12 V supply. I used a computer power supply unit (PSU).

In order to automate the temperature regulation, the thermometer is connected to an Arduino board controlling a relay, which when the beer is too warm, turns on the PSU and hence the cooling system. I avoided using a PID controller, not wanting to deal with tuning coefficients. So I wrote a very simple code for the automatization of the cooling process. First, I performed some preliminary tests turning on and off the cooling system manually and looking at the temperature evolution. As it turned out that the system is very stable and predictable, I came up with an intuitive algorithm that appears to be nonetheless efficient. In order to keep an eye on my beer’s temperature from anywhere, I connected the Arduino to a WiFi module and eventually to an app on my smartphone. This I developed myself using Blynk, a freeware platform for developing apps in this framework. Interactive modules in the app allow me to track the temperature evolution, to set target temperatures and to turn on or off the cooling system. In order to have a backup, the temperature data can be sent to any email address.

Finally, I put in place a CO₂ harvesting system and chose the common two-jar system. During cold crash after fermentation, when there is a pressure decrease inside the fermenter, the two-jar system sucks back CO₂ instead of oxygen, avoiding oxidation.

Tools and Materials

• 3.1-in. (8-cm) thick polystyrene panels
• Polystyrene cutting device
• Polystyrene-safe glue
• 1.6-in (4-mm) thick
• Plexiglas® panels
• Silicone sealant
• Waterproof DS18B20 digital temperature sensor
• ¾-in. silicone hose
• Small aquarium water pump
• Peltier water cooler
• Cheap/old computer power supply unit
• Arduino Uno
• ESP8266 WiFi board
• Relay
• 2 small jars for CO₂ harvesting system
• Test tube