September was warmish in many places around the world including [Ole]’s native Denmark. But that did not stop him from brewing lager flavored with plums from his own garden, and neither did his indifference to lagers in general.
Lager fermentation requires a consistent, low temperature. While many homebrewers might modify an electric refrigerator, [Ole] wasn’t interested in the cost of running a second one just for brewing beer. Instead, he built a climate box to work with the cool temperature in his garage. Starting with scrap wood from other projects, he lined the walls with polystyrene and put a layer of wood on the floor to help support the fermentation bucket.
Maintaining a consistent temperature in the box called for both heating and cooling. He pulled the Peltier from a 12V cooler meant to run off a car’s cigarette lighter, and used a spare ceramic heater that was lying around in case his primary reptile warmer went on the fritz.
An Arduino and a custom shield drive separate PID controllers for the Peltier and the heater. The shield has a temperature probe, and he extended the USB outside the climate box so the PIDs can be adjusted without disturbing the inside temperature. The schematic, board file, and code are all available in a zip you can get from his post.
The Peltier couldn’t quite compensate for the overly warm weather and the heat caused by the fermentation, but it was stable enough to produce a nice, plum-flavored lager he has dubbed Lektor Blommes maltbolche, which is a triple Danish pun he explains in the write-up.