Towards the end of Enrico Fellini's 'The Rehearsal' - there is a scene in a
busy bistro. Watch carefully as the very professional barista pulls a shot
from a lovely 3-group side-lever Gaggia machine. Notice that he pulls the
lever down and holds it for pre-infusion, then he rapidly lifts the
lever up a few inches and pulls it back down into preinfusion and holds it for
about 10 seconds more before releasing the lever to complete the pour.
This 'double-pump' move was frequently used on this vintage of commercial
lever machine - the theory behind it being that if you initially saturated the
puck and allowed it to swell, and put in another charge of hot water
then you'd get rich, syrupy 'mouse-tails' during the initial pour.
I've often wondered if the design of the E61 grouphead with its preinfusion
chamber wasn't supposed to mechanically emulate the classical barista's
I wondered if the fluid dynamics of the commercial machine's relatively flat and shallow 58mm puck was different from the tall and narrow 45mm Ponte Veccio basket, and after burning my way through nearly a pound of home roast and tasting a fair number of double ristretto shots (buzz, buzz, buzz) from my commercial and PV Lusso machines can say that this technique appears to be equally applicable to both 58mm and 45mm spring machines. Sadly, I don't believe that this move is applicable to Pavoni or Olympia direct-acting lever machines, because once you've started the pour you won''t introduce a further water charge by lifting the lever and risk fracturing the puck by pulling the lever up.
Ironically, while rather dramatically intensifying the flavors and body of the shots, this technique also does appear to significantly diminish crema production, especially early in the pour. Also, as a point to note, the same vintage baristas would not collect any of the pre-infusion drips, claiming that "They are bad liquor, very bitter!" and would sometimes not put the cup under the spout until the first drops had merged to make true 'mouse-tails.'
I must confess that I've not tried this trick, as I'm far too cheap and greedy not to want guzzle every drop ....
Anyway, do go and rent 'The Rehearsal' it's an interesting commentary on Italian life and politics in the early 60's, and you get a free espresso tutorial from a 'golden-age' barista at no extra charge.