Here is a pic of the crema that the Arrarex Caravel (open-boiler gravity-fed) can produce when the piston is pushed to pressure extremes its little o-oring can hardly tolerate:



Preinfusion: ~20 seconds. Two additional pulls of the lever, maybe 20 seconds in addition to the preinfusion.

It's hard to go wrong when the water is at the right temperature

Normally with the Caravel I go for less body and a thinner mouthfeel, and pull a sweet lungo with flavors more delicate than intense.

This is Intelligentsia's Papua New Guinea, btw, delicious, but happily not a coffee in their Get High Sell High program, and so one that I can afford

Regards
Timo
P.S. Not a drop from the spout that didn't go into the cup.
P.P.S. In the crema, do you see the silhouette of a man wearing a fedora, walking to the left, dragging a carpet bag behind him? Or Donald Duck?

When the Romans wished to quarry stone, they would drill holes into the stone with an auger and then hammer pegs of dry wood into them. These pegs they would then douse with water, and the hydrostatic pressure of the water being absorbed into the wood was so strong that it split the rock into slabs.

The swelling of the puck operates under the same principles and is a primary factor in the establishing the pressure profile and thus is very important to the extraction process. Illy (who alludes to the quarrying practice described above) writes as follows in ch 8.5.4 of The Chemistry of Quality:

...a chemical hydration of the organic material ... takes place. The water... is bound...in a state differing not only from the normal liquid state, but also from that of interstitial water, which is subject to laws of capillary phenomena.... During expansion, the coffee grounds exert a pressure comparable to that of the wooden wedge used to cleave marble blocks.... The actual expansion of the cake varies with blend, roasting degree and dose, and determines the exact head space (around 5-6 mm) needed to prevent over-compacting....

Regards
Timo