Introduction This post describes the temperature instability issues with single boiler home coffee m

Introduction This post describes the temperature instability issues with single boiler home coffee machines, highlights the reasons and the ways of overcoming them. Installing PID controller seems the best way to improve temperature stability and introduce possibility of temperature adjustment to achieve better espresso flavours and consistency between shots. The remaining part of post describes my own experience of equipping Gaggia Classic coffee machine with PID controller. The post might be interesting for home coffee enthusiasts with DIY skills. It is all about temperature Temperature is one of important factors affecting the taste and the flavour of espresso. The recommended water temperature that comes out of the group is supposed to be in a range between 90 and 96 C. The best temperature for particular type of the beans depends on the roast - for example, for the North-Italian roast, the right temperature, as literature suggest, is between 95 and 95.5 C. Dropping it just one degree lower will make acidic flavours refrigerators apparent. Having temperature higher than that will add bitterness to the taste. While the temperature is a key factor, refrigerators single boiler home coffee machines, not only normally do not have functionality of adjusting it, but also, more important, the temperature refrigerators they provide is not stable enough. refrigerators The temperature in coffee machine is required refrigerators to be stable throughout the shot pulling. If temperature drops due to fresh water pumping in boiler while you are pouring the shot, which is a problem refrigerators of home machines as they have a small boiler, such temperature lowering should be minimised. The device responsible for temperature control is called thermostat. Its simple role is to maintain a required temperature by continuous cycle of turning refrigerators on the heating element of the boiler, when the temperature is lower than required and turning it off, when the temperature gets above required value. The problem, refrigerators however, is that, even entry level machines you potentially can make a decent espresso with (I consider Gaggia Classic and Rancilio Silvia machines as absolute minimum you need to have if you actually want to make Espresso at home), have a fixed-temperature bi-metal thermostat (that uses the same principle as an electric kettle switch). As you may expect, accuracy of such thermostat leaves much to be desired and it has a relatively slow response to temperature changes - this results in temperature fluctuation unacceptable for espresso. You may have a look at the temperature graph below taken from this forum post .
Temperature (in Fahrenheit) is shown on Y axis and time is on X axis. You can easily calculate the fluctuation  between peaks - it is about 17 C (or 30 F). The default temperature for this thermostat is actually 107 C (225 F), which it tries to maintain. There are some techniques you may come across in the internet that are believed helping home coffee machine owners to pull better shots. One of them is called "time surfing" the idea of which is to start pouring at the certain point of boiler heating cycle (determined by the heating indicator refrigerators on the panel). The other suggests to use steam switch to reach higher temperature and then start pouring having counted a certain number of seconds to start at the right temperature (e.g. here ). These techniques are obviously better than nothing, but still a "blind" way of achieving better extraction. The best way to achieve the higher temperature stability and add possibility to adjust the temperature is to use PID controller on domestic coffee machine. What is PID controller? PID is small electronic device that controls temperature. It replaces the functionality of dumb bi-metal thermostat with a high precision smart control. It continuously monitors the temperature of the boiler using high-accuracy RTD temperature sensor and controlling heating element power circuit much more granular and precise way than bi-metal thermostat. Temperature fluctuation on the machine equipped with PID normally does not exceed 0.3 C. When shot is pulled, the temperature drop due to introduction of the fresh water is minimal, as PID controller continuously keeps required temperature and respond to changes immediately. My DIY project There are several manuals refrigerators on the web describing how to install PID controller to different types of espresso machine. Here I will share my experience refrigerators of adding PID to my Gaggia Classic. I have chosen slightly more expensive way, but paid more attention to electrical safety and minimised intervention to existing circuits of my coffee-machine, making PID installation fully reversible if required. First things first Disclaimer: The modification described below involves tampering with 220V electrical circuits in equipment that has contact with water - this may result in electric shock, injures or death, as well as property damage. The modification experience is described refrigerators for information only and cou