Working for the manufacturer of one of the machines mentioned in the previous posts it is obvious that my opinion could sound a little partial to some of you… this said I will try to be as scientific as possible trying to explain the process that has brought Nuova Simonelli to design its steam system. I will highlight 4 sets of features that I personally like and endorse about our lever system vs. other systems available on the market:
1) Ergonomic features: Aurelia's steam system is the result of a design partnership with the European Institute of Ergonomics and Psychology that has studied the interaction between machine and barista. One of the main results of this study was the steam lever design: first of all it was preferred to a knob design because the rotation movement of a wrist, if repeated hundreds of times every day, can lead to a disease called “carpal tunnel syndrome”.
What is also different about this lever design is that it can activate steam by using only one finger: the upper portion of the lever has a rounded profile to better support the “arch” created by the index finger while pulling down the lever, the portion facing down instead is flat in order to allow operator to push up the lever with no effort and good grip.
2) Push / Pull: this is the nickname we gave to this system. If the operator pushes lever up, as soon as it is not held in position, lever will go back to the off position ( I believe this is a nice feature for the initial / final steam purge). If the operator pulls lever down, it will immediately go and stay in the maximum steam power position, which allows operator to have maximum steam efficiency from the very beginning of the steaming process. When it is time to shut off steam, it is sufficient to gently push the lever up with one finger to disengage it from the max power position and it will go immediately – thanks to the valve with spring operated piston - in the off position (this in my opinion greatly reduces the risk of having unwanted heat / steam in milk which can happen with knobs or systems that don’t go automatically to the off position. It also expedites production in really busy locations).
3) Lever material & valve design: steam lever, which controls the activation mechanism, is made of “auto-lubricated nylon” a material we have “borrowed” from surgical applications that is indestructible, also, the valve design prevents from compressing the piston gasket (this way avoiding leaking of steam valve gasket which sometimes happens with strong baristas using knobs…)
4) Steam tip design: we have four holes steam tips available in different hole dimensions. The most popular ones are 1.2mm (which are normally used for small pitchers) and the 1.5mm (which are used with our insulated “cool touch” wands and for 32oz. ++ pitchers). Combining different hole sizes with maximum steam power gives a standard measurement of steaming efficiency: in the same coffee shop there might be different steaming results from operator to operator that are using knobs or systems that don’t have set points, because there are no reference points available to the barista to read steam's flow rate.
The fact of practically having maximum steam power from beginning to end of the steaming process (given the fact that boiler pressure is not substantially changing from shot to shot), associated with the availability of different hole sizes, allows to control and standardize steam’s flow rate leading to a more consistent result.
Again all the above comes from my experience and I understand there is not the perfect system out there because it depends on personal habits, but if you are interested to learn more about this you can use the following link http://www.nuovadistribution.com/images ... 0Paper.pdf