There have been alot of talk lately about presure profiling during the brewing process of espresso. In fact, the new bread of pump machines that have been coming out from La Marzocco, Slayer and Synesso and other are incorporating the ability of the baristas to custom profile the pressure during a shot. Amazing, pressure profiling is not "new" because it has been the inherent feature of spring lever espresso machine; it is simple physics that as a compressed spring slowly release it energy, toward the end, the amount of force is less and will taper off. So essentially, the new breed of machines are trying to emulate the feature that have been available in spring lever machines that had been invented in the 1940s. However, of course, they are profiling pressure at constant stable brewing temperature.
I thought about another perculiar characteristic that spring lever espresso machines have but was not able to confirm my thinking until I stumbed upon the youtube video above. Basically, the barista is measuring the temperature of water during a shot of espresso made by a commercial lever machine (the machine is a very nice Victoria Arduino Athena by the way). The Scace device shown that the temperature of the brewing water decline during the duration that espresso shot happens and this confirm my previous thought about lever. This basically happens because the group head of the lever is wicking away thermal energy of the brewing water thus creating a declining temperature profiling!
So the soft and velvety shots of espresso from lever machine might be attributed not only to the declining pressure profiling but also the declining temperature profile as well. This is interesting because there curruntly do not exist any pump machine that can do both pressure profiling and temperature profiling ( HX machines do have an imcreasing temperature profile during the duration of long shots). Also, not all lever machine has this property, I know for sure the Pavoni group head continue to increase in temperature during the duration of the shot (as well as probably machines that has groupheads directly connected to boilers).
It will be interesting to see in the future, pump espresso machines having this temperature profiling capability!