Contact screenby Simone Forgia, Claudio Santoro
The first time using a lever espresso machine and flushing the group, it might have happened to everyone to remain impressed by the force with which the water comes out of the shower screen. In fact, unless you are using an open boiler or double boiler machine, the water usually comes out with a pressure of around 1 bar and during extraction this pressure can even exceed 9 bars. Even though with time you can get used to the violence with which the water comes out, the same cannot be said for the coffee. In fact, if the puck is not prepared with extreme care, when exposed to such a force every little imperfection is accentuated and often even if everything seems to be done perfectly, some problems that we will eventually find in the cup will show up.
For this reason, many people have recently started thinking about ways of protecting the coffee puck and mitigating the force with which it is hit by the water jets; the most common solution of all is to use a paper filter. Although this system is partly effective, it nevertheless presents several problems such as the continuous waste of paper and the loss of time in cutting out the filters as in most cases they are not already available on the market of the exact dimensions.
In recent months, however, a solution has been presented from the Taiwanese brand BPlus, which, after dozens and dozens of tests on materials with different properties and structures, has arrived to the version currently marketed as the "contact screen" (also known as puck screen). This screen is very solid, heavy and has a metal structure with a dense mesh.
Thanks also to its thickness of 2 millimetres and its characteristic structure, the water jet is broken up and redirected in hundreds if not thousands of directions before it can reach the coffee, ensuring a very gentle and even flooding of the coffee puck. This gentleness translates into a great reduction in the formation of channelling issues and is particularly evident with light roasts which, being less prone to water absorption, present this problem much more frequently. This can be seen visually, statistically and sensorily. Visually, because as long as no other gross mistakes have been made, at the end of the extraction the puck is always perfectly intact and has no channels. On a statistical level, as measurements taken with a refractometer show an average increase of about 2% of the extraction yield; and finally, on a sensory level, because when tasting our espresso, it is possible to perceive an increased quality of the shot.
Another great advantage of the contact screen is that it prevents the coffee from directly touching the shower screen thereby preventing the latter from becoming dirty and simplifying the process of cleaning. The only precaution to be taken is to slightly increase the extraction temperature as the metal mass of which the contact screen is made will absorb some of the heat. The manufacturer recommends increasing the temperature by 2-3°C, but from our experiments 2°C should be enough.
Although its size is accurate in relation to the diameter of the filter, in some cases we still experienced a slight "doughnut effect" at the beginning of the extraction as the water could still find an easier way around the edges. This happened more often with large doses, as the filter walls are usually slightly conical and therefore a few tenths of a millimetre wider at the top.
Still concerning the dose, another thing to keep in consideration is that by adding the extra thickness of the screen on top of the ground coffee, in some cases there might be the necessity to slightly reduce the amount of coffee used or get a bigger filter.
The contact screen is therefore one of those accessories that may apparently seem of little importance but can actually have a big impact on the quality of our espressos, increasing the success rate. Although it may add an extra step to our daily workflow, it actually makes the cleaning easier and therefore we are sure that its popularity will only increase.
Magnification of the metal mesh