The Isomac Zaffiro is the chosen espresso machine for experimenting with the PID controller. The Isomac Zaffiro is IMHO a very good espresso maker. You can read a detailed review on coffeegeek.com.

The reason for chosing this machine is simple - the author owns one.

The first thing to do was to measure and plot the temperature curve of the original unmodified Zaffiro. Since this machine is renowned to be a temperature stable machine, the result was quite surprising (see digram below).

As you can see, the temperature differs from 88 °C to 102 °C with a period of approximately 7 minutes.
Read here why thermostats are performing so badly.

It should be noted that the temperature was measured in the water boiler tank, not in the brewing group head, where the temperature might differ a bit less. But it is still quite surprising.

This means it will be pure luck to brew at the correct temperature if we don't have a thermometer or do something like temperature surfing.

The next step in this project is to build a PID controller prototype.