A few weekends ago I went around to Andrew’s place to brew some beer. He’d been given a Coopers Homebrew Kit for his 21st birthday which hadn’t been used, so after replacing the hopped malt concentrate that had expired a few years ago, we set about sterilising the brewing vessel, boiling the water, adding the sugar and concentrate and finally the yeast.
The instructions suggest that the particular strain yeast will ferment best between 21 and 31°C. There’s a stick-on heat sensitive sticker that gives some indication of temperature, however if this is covered by a warming blanket, it’s a bit hard to read. Also, it doesn’t do a good job of measuring fluctuations over time, leaving us with questions such as was the mix getting too cold overnight?
Luckily, I had a Arduino shield that I assembled at linux.conf.au: the Pebble. Designed by Luke Weston of MobSenDat fame, and put together as a kit by Jon Oxer and his colleges at the Melbourne hackerspace. The features we used were the DS18B20 temperature sensor and the 4-line LCD display. The Akio scheduling framework was used to poll the temp sensor and update the display with the current, minimum and maximum recorded temperature. The current reading is also sent down the serial port for logging. The Arduino sketch can be found here.
An OLPC XO-1 was used for the logging and to provide power. This meant that we could have monitored it over the network; my plan was to use David’s HOWTO to set up a Munin graph. This didn’t eventuate for this brew, but perhaps will be implemented for the next.
Post-fermentation we took a look at the logged data. As can be seen below, there is a daily cycle as the day/night ambient temperature change occurs. There is also an overall downward trend. As the yeast metabolises the sugars into ethanol, I imagine they become less active over time and hence give off less heat. Or it could have just been a warm day followed by successively cooler days (probably not though – brewing started on the forth. But perhaps Andrew was running his air conditioner?). Another addition for next time would be to I will look at the correlation between the logged data, daily temperature and room tempature.