Via the protofusion blog, Matthew Reed writes about hacking a Gaggia Classic espresso maker to make more consistent shots:
The ability to make good espresso is one of the most coveted skills in the coffee world. The rich body and complex flavor profile of a well-made shot brings the beans to life with a depth that other brewing methods fail to achieve. But espresso is also among the more complicated ways to make coffee. Fine grinds, high pressures, short brew times, metered doses, and precise temperatures all work together to create the perfect shot – but a variation in any one of these variables can just as easily render it undrinkable. Making consistently good espresso requires consistent brewing parameters.
Unfortunately, traditional consumer-grade espresso machines are not very good at keeping water temperature consistent. They typically manage the boiler temperature with thermal cutoff switches, which have a large temperature range, switching off the heater when the temperature reaches the top of the range, and switching back on when it gets to the bottom of the range. This can result in temperature swing of 10°C or more, but espresso requires a precision of at least 1°C for reliable results. Because of this, many home baristas will learn to “temperature surf” by measuring the boiler temperature at various points in the heating cycle and tracking the time after the thermal cutoff switch turns off to hit their desired brew temperature. This technique is very tedious to execute correctly and is subject to variations in individual machines and environmental conditions.
The best way to keep the boiler temperature consistent is by implementing a PID control algorithm, which is designed to optimally regulate temperature and can easily achieve sub-degree accuracy. There are many commercial PID controllers available on the market, but they each have drawbacks such as size, cost, and customizability. To overcome these hurdles and create a solution that meets our temperature control needs, Protofusion has developed a tiny open-source PID controller called Therm.
Start to finish, it took Matthew about 2 hours to complete the project. Some comfort with tools and soldering is required.
See all the details on the protofusion blog which has complete parts, instructions, and pictures for the project.