Kees van der Westen
 

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Mirage Idrocompresso


Mirage Duette Idrocompresso with Veloce bodywork.

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General observations

We are offering the lever group equipped version of our Mirage , called Idrocompresso, for several years now. Many a time we observed a certain fear for these lever machines. People often think a lever machine must be very difficult to operate, only very experienced baristas (preferably from Italian origin) can pull a decent shot, pulling those levers must be very tiring, they overheat quickly, etc. etc. All these pre-conceptions will be dealt with and thrown out of the window in the accompanying explanatory text. We`ll try to explain why and how our Mirage is surprisingly easy in use and brews a magnificent espresso with voluptuous crema time after time.

Interestingly, the levers are currently enjoying a renewed interest from baristas all over the world. So much so in fact, several manufacturers actually declare they strive to copy the technical specifics of the lever group with their pump machine.
They however focus on just one of these specific levers aspects, the pressure profile, conveniently forgetting all other, quite probably even more important, aspects.

Please do read on, we`ll explain all these aspects.

Considerations of the Idrocompresso in today`s world

The lever group is a very old system, developed end of the 1940`s, to achieve the essential of espresso: forcing hot water with high pressure through the ground coffee. Despite it being old, despite the development of pumps to raise the necessary pressure, despite the development of flat line temperature machines, the lever is still widely recognized to deliver the creamiest crema, best buttery mouthfeel, highest amount of solids, oils and fats in the cup. What`s more, these desirable benefits are easy to achieve, the lever group is simple to operate and very forgiving.

It is no wonder these machines can still be found in many tasting rooms, at roasters all over the world. In Naples, the centre of coffee in the original country of espresso, 90% of all espresso machines is equipped with levers.

The reasons for the superior extraction qualities of the lever are easy to explain.

First of all the infusion. As soon as the piston is at its highest position (lever fully down in lock position) water flows under low pressure into the space underneath the piston, on top of the ground coffee in the filter basket. Quickly a short column of water starts sinking into the coffee. As this column has almost the same diameter of the coffee bed, this infusion results in a very soft, evenly spread and thorough saturation of the ground coffee. This infusion generally takes 4-7 seconds.
Secondly, when the first drops of coffee appear at the bottom of the basket (or spout of the filter holder) as a sign infusion is completed, the lever can be lifted out of its lower locking position. The strong spring on top of the piston now starts to force the water through the coffee. A fully compressed spring executes great force, this force slowly diminishes as the spring relaxes. The pressure profile on the current Mirage starts with an infusion pressure quickly going from 0 till line pressure, followed by a spring pressure starting at 9 bar with a smooth leveling off to 5 bar when the piston hits home. After this pressure diminishes to 0.
Note: after unlocking the lever at the end of the infusion, the barista is free to attend to other matters, the process develops and stops automatically.
Thirdly, next to the pressure profile, the Idrocompresso has a built-in temperature profile. As both the inner cylinder and piston are made in brass, a good heat transferring material, the water residing longest inside the cylinder, in fact the upper part of the water column, will see some of its temperature absorbed by the surrounding brass. So the temperature of the water forced through the coffee slowly declines during the entire extraction.
Fourth, the rotating pump on a pump machine has a shaft with four vanes. These vanes actually move the water from inlet of pump to outlet with great force and speed. Each time one of the vanes passes the outlet towards the machine, a pulse is created. This results in high pulsating water directed to the coffee grounds. This is in stark contrast with the very smooth and linear only movement of the piston with spring of the lever group.

Although it has nothing to do with the extraction process itself, there is another very strong attraction to the lever group machine. This probably even is the strongest appeal for many: the theatrical effect of these levers going up and down. A barista at full swing behind a Idrocompresso is a very exciting sight indeed. Pure espresso drama in fact. Even to people who have never actually seen a lever machine, it almost unconsciously represents the one and only true espresso machine, the godfather of espresso preparation. Its strong artisanal character translates into the ultimate in espresso quality in people`s minds.

Combining the above with the pure simplicity of the system, the straightforward operation, ease of maintenance, it is easy to see the Idrocompresso is a vital force for today’s knowledgeable barista`s and espresso connoisseurs.

Construction of the Mirage Idrocompresso lever group

In short
The levergroup consists of a large cylinder. Inside this cylinder sits a piston. When not brewing the piston sits at the bottom of the cylinder. The piston is connected by a vertical shaft to the cantilever turning mechanism on top of the cylinder. On top of the piston, around the vertical shaft, a very strong spring is installed. When the large lever is pulled downwards the piston inside the cylinder is pulled upwards and the spring gets compressed. With the piston at its highest point four holes in the cylinder wall are cleared. Water from the thermo-syphon heating system runs into the cylinder and fills up the space between coffee and underside of piston.
By releasing the lever from its lower locking position, the spring starts to push the piston down, the piston in turn forces the water through the coffee. Simultaneously the lever slowly returns to its upward resting position. When the piston has arrived at its lower resting position the extraction has stopped automatically and the lever has returned to its original starting position.

In detail
The Mirage Idrocompresso group consists of a lower cylinder part, attached to the frame of the machine and a removable upper moving part.

The lower cylinder part is made in brass.
The outside is highly polished and chromed.
Inside the large cylinder a separate cylinder (liner or sleeve) is installed. The piston runs in this inner sleeve. The sleeve is also made in brass, but the inside where the piston runs, is technical hard chrome. This hard chrome makes it extremely wear resistant.
The sleeve can be removed, there are two o-rings between sleeve and outer cylinder.
   
The upper group part is held onto the cylinder by four bolts. After undoing these bolts the entire upper part, containing lever, turning mechanism, spring and piston, can easily be pulled from the cylinder.
The cantilever system has three bearings. Two identical ball bearings at the outside, one wide needle bearing in the centre.
The spring is made in stainless steel.
The piston is in brass and has 4 rings. One rubber ring each is located just above and under the 4 holes in the cylinder, when the piston is at its resting position.
Another identical rubber ring sits at the bottom of the piston, to keep the brewing water under the piston during the extraction process. These rubber rings have a special V-shape. The more pressure they encounter, the more their lips are pressed against the cylinder wall and piston to prevent any loss of pressure.
The fourth ring is a guiding ring in Teflon, to ensure the piston always retains the same distance from the cylinder.
The group screen is a perforated stainless plate. Not covered with wire mesh, so easy to clean with a quick wipe. This screen is clamped around the outer wall of the cylinder, with its teeth into a groove. It is simple to remove and re-install with our specially developed “plopper” tool.