If your machine is fed by line pressure, you can use the middle lever position to "prewet" the coffee puck. An interesting discussion of this here
and excerpted below.
olypdd wrote:You make an interesting point, but in the case of my machine, as soon as I engage the pump, the water is pumping out at what would appear to be enough pressure to hit the puck with a fair amount of force, vs a mere preinfusion (passive release of static line pressure). When there is a loaded portafilter in the machine, it does ramp up to brew bar in a matter of seconds. When I raise the brew activation lever with the machine off, water runs out the brew group at a leisurely trickle, that which would appear to saturate the grounds in a manner consistent with the idea of preinfusing them in a way so as to not disrupt the integrity of the tamp, and to counter the ability for water at brew pressure to channel along side the puck, vs saturating it uniformly.
Perhaps I misunderstood what exactly "defines" preinfusion as it relates to the operation of an E-61 brew group, but based on what I have read, and derived from speaking to Chris Coffee, it seems reasonable that initial soaking of the grounds at just over static pressure vs live pump pressure provides less invasive pre-infusion.
I did a little experimentation as documented in The Secret Life of Ristrettos
, excerpted below:
While my comment isn't directly
related to this thread, lately I've been experimenting with extraction rates as part of the Vetrano wrapup. That, plus Ken and Jim's The Impact of Preinfusion on the Taste of Espresso Shots
has me thinking about extended preinfusion for E61s, despite their native capability.
Combining the two ideas, I increased the water inlet pressure to three bar. When the lever is up and the machine is off, water flows readily through the grouphead. The "rebound" time for the Vetrano is 30 seconds after the flush, so I reserved the last 10 seconds for additional preinfusion. Specifically:
- Flush as usual; start preparing the portafilter (or prepare basket separately and drop it in later)
- Lock in the portafilter
- The heating element will click off 15-20 seconds after the flush; once it does, turn off the machine
- At the 20 second mark, lift the lever up. The mains pressure will preinfuse the puck ever-so-gently
- After 30 seconds, turn on the machine. Since the lever is still up, the pump begins immediately.
So what does this have to do with ristrettos? Getting the grind perfect for ristrettos on heat exchanger espresso machines can be tricky. Too slow a flow and the HX will overheat, producing a doubly-bitter shot (partially from high temperature, partially from overextraction). Too fast a flow and the rich, sweet, punchiness of a ristretto can be lost. The extra preinfusion appears to increase the margin of error.
As a rule of thumb, ten seconds of (extra) preinfusion equals a grinder adjustment of two millimeters coarser on the Mazzer Mini, or a reduction of coffee equal to approximately 1.5 grams (*). Running the mega-sized preinfusion "softens" the puck and opens a wider window for good extractions. My results so far for ristrettos are improved, though the opposite occurred for regular doubles, where the flavors became muddy and flatter.
(*) Don't take these numbers too literally, they are meant to convey that the effect is very small.
The machine off-on trick avoided any quibbling about the "3/4" position being used for preinfusion. I'm not convinced of the merits of this approach, but it's worth further experimentation.
olypdd wrote:Wouldn't the same ramp up to pressure there serve to preinfuse the coffee as you mentioned with the E-61. In fact, it seems to ramp up more slowly than my Vetrano rotary pump, but I haven't timed the two. Perhaps I will do this.
It's not easy to compare different grouphead designs; adding different pumps makes it even more challenging. That was a surprising lesson I learned in Pressure profiles, preinfusion and the forgiveness factor
, i.e., the assumption that a slow pressure ramp up = preinfusion = high forgiveness factor isn't true. I thought it didn't make sense, but several others (including Jim) have confirmed my findings that the A3, which ramps up as fast as a rocket, is a forgiving espresso machine.
Yes, prewetting may provide a more even extraction because it allows the coffee grounds to expand and fill in cracks in the puck. But you'd be better off fixing the grind/dose/distribution/tamp defects that produced those imperfections in the first place, and only then play around with pre-preinfusion. Note that Dan used an extended preinfusion for reasons of taste, not to fix channeling.
No offense intended. We all go through this with the bottomless PF. It's a great tool for improving espresso technique - and teaching humility.