Surely you know them, in the 50's they sat at every bar in Italy and elsewhere in the world. The espresso was prepared using a water press, which was created by a strong spring with a piston controlled by a long lever. Thanks to this innovation, crema has already appeared regularly on espresso and the drink has been enriched with many aromas unknown until then. By the way, some baristas will not allow these coffee machines, which are still made to this day. Anyone who has ever worked with this coffee machine will agree with me that the espresso prepared on this type of coffee machine is fuller, more complex and rounder.
Like everything, this system has its downsides. In the first place, it is necessary to mention the physical demands of preparation. If you have to prepare 100 espresses in a row, it can be a challenging sport for anyone. Potential danger - even if the coffee machines are equipped with a safety device against the piston running idle, it happens that the lever shoots sharply upwards in the absence of water in the cylinder. Alas, if your chin is in the trajectory of the lever. Enormous force can easily shatter your jaw. The inconvenience of the system to the precise setting of the coffee grinder is also an inconvenience.
What happens during extraction?
In the beginning, you pull the lever all the way down. This will raise the piston and allow water from the boiler to fill the cylinder above the port filter. The water has a pressure of around 1 Bar and freely moistens the coffee puck in the lever. This phase is called soft pre-infusion, with La Marzocco coffee machines all models marked MP can do it. After about 5-6 seconds, a drop of coffee will optimally drip from the port filter outlet. This phase should not last longer than 10 seconds. This is followed by a gradual release of the lever upwards. At this moment, the spring pushes the piston with a pressure of approx. 12 Bar. As the spring stretches, the pressure acting on the piston slowly decreases. This is an important moment, the pressure goes slowly from 12 Bar to zero. Why is coffee prepared in this way extracted so well? I think it has to do with the amount of aromatic oils in the coffee puck. At the beginning of the extraction, when there is the most of them in the coffee, the highest pressure acts and the coffee "bears" it does not burn. As the oils in the coffee decrease, so does the pressure. As a result, the oils are perfectly extracted without more unpleasant astringent substances being extracted from the coffee mass. Thanks to the La Marzocco Strada coffee machine, this pressure profile can be easily imitated and can be fine-tuned in various ways. So today you can easily try how tasty coffee from a historic device, if you upload this profile to the EP version of Strada.
The pressure profile for Strada is shown here.