Bezzera Strega modsby Marc Assinck
The Bezzera Strega is a popular single boiler spring lever machine known for its versatility and great value for the money. The grouphead is supplied with water from a boiler via a heat exchanger system and it is heated by two electrical resistances. The pre-infusion is delivered by a vibration pump and the group has two springs that work in conjunction and are operated by the lever. There is a bigger “main” spring, and a smaller “booster” spring inside the main one. Together they produce over 12 bars of starting pressure for the extraction, so there is an equilibrium with the standard pre-infusion pressure by the pump, which is also about 12 bars. This standard configuration already produces a great espresso, as the extraction has the typical declining pressure profile that characterizes a spring lever machine; however, there are some interesting mods that can possibly enhance the performance even more. Let’s break down the three main modifications that can be made and their effects.
Plumbing the machine
This mod is of course not exclusive to a Strega, but the generic benefits also apply to it: never having to fill the tank with water, never having to clean it (due to growth of micro organisms in the water over time), and never having to walk around with a full drip tray provides a lot of ease of use. In addition, this feature also ensures better temperature management because when the machine is not plumbed in and the tank is filled with water at 15°C for example, just after a few hours the same water can easily reach 35°C or more. This means that the water that enters the heat exchanger system in the morning, and the water that enters it later in the day will have a 20°C temperature difference and the difference in taste is quite notable. When the machine is attached to the main line instead, the water that enters the heat exchanger is always at the same temperature, so it delivers a more consistent brewing temperature throughout the day and if an in-line filter is also installed, the interior is even protected from scale build up.
Interesting to note is that since the pre-infusion is done by the line pressure, it makes sense to also install a pressure regulator, which then allows for an adjustable pre-infusion pressure. Depending on the delivery of the water line, this pressure can be varied between 1 and 3 bars or in some cases even more. Another advantage is that, without the pump, the machine operates in almost complete silence, enhancing the zen factor when pulling an espresso.
The Bezzera Strega is available in a “top” version, which has the tank / water line switch possibility already built in, but it is quite easy to do this mod yourself, and there are kits available for this on the market.
A fun feature is that when the pump is left in place, and is made “switchable”, one can also still make full “pump shots”, allowing the guests to directly taste the difference between a pump and a lever shot, which is absolutely notable.
Inner / booster spring removal
Another very interesting modification is to remove the smaller, inner spring. This mod requires a special tool but allows to lower the peak pressure from 12 to around 8 bars. The lower extraction pressure also requires a coarser ground and the combination of these two corrections provides a notable taste improvement. Most users describe it as if the spectrum of aromas is wider. Many Strega owners use a 14 grams EPHQ filter basket (filled to 18-19 grams), as this one works really well with a lower pressure.
In order to improve this mod even more, it is recommended to change the standard pump with a version that has a more gradual pressure-build up and a lower end-pressure. Alternatively, an even better solution is to use it in combination with the plumbing of the machine and take advantage of the line pressure for the pre-infusion. So even though the Strega is a heat exchanger machine, this spring modification in combination with the use of the water line pressure, gives it somewhat of the low pressure pre-infusion character of a classic dipper; the difference is, however, that if one wants to modify the pre-infusion pressure of a dipper it needs to be done via increasing or decreasing the boiler temperature. This means that a change of the pre-infusion pressure also affects the brewing temperature. With a Strega on the other hand, when the water line pressure is used in combination with a regulator, this is not the case. One can keep the boiler water at the same temperature, but play with different pre-infusion pressures. Londinium does the same with their new R24, but they use variable pre-infusion pressure via the rotary pump. This mod is fully reversible, so no harm done if you do not like the different character.
Adding a PID
Since the Strega does not have a thermosyphon system, the grouphead is heated via two small electrical heaters. In the standard configuration, these heaters are operated via two on / off thermostats. Unfortunately, this means that the temperature has quite a big “dead-band” (temperature fluctuation) and also cannot be adjusted easily. Adding a PID controller to the grouphead heaters improves both of these things; the “dead-band” is a lot narrower, providing more consistent shots, and the temperature of the grouphead can also easily be adjusted and tuned to different beans and ground / dose combinations.
It is also possible to add a PID to control the water temperature of the boiler; however, this is a less common mod. As the water temperature is “integrated” via heat exchanger and the thermal mass of the grouphead, the improvement in terms of temperature stability can be debated (as with a PID on any heat exchanger machine), but an interesting and a fun modification nonetheless.
For the PID mod, one can buy complete kits, that consist out of a temperature sensor, the PID device and an “SSR” (Solid State Relay). These components can be fitted inside the housing of the Strega. Another solution for a plumbed machine, where the water tank is not used, is to replace the plastic tank with a “box” that contains the components of the PID upgrade as can be seen from the picture below.
PIDs fitted inside the housing of the Strega were the water tank was previously located
In the spectrum of classic and high-end lever espresso machines, the Strega is sometimes a bit undervalued, but it already makes a great espresso straight out of the box and for those who like to experiment, the benefit of it’s inherent design is that it offers a lot of possibilities for tweaks and upgrades. The Bezzera Strega is therefore a machine that can easily be turned into a very flexible, good lever and that can even compete with more high-end competitors.