HB wrote:The majority agree the timing starts when the water first makes contact with the coffee, i.e., when the pump starts.
Regardless of majority opinion, this is not an entirely trivial issue. Water contact with coffee grinds proceeds downwards, from the top of the puck to the bottom. On preinfusing E61 groups, it may take 7-8 seconds before the entire puck is saturated, and espresso droplets appear. This "dwell time" is 30% of the recommended pour time. On my Spaz S1V1 (rotary pump, no preinfusion) the dwell time is about half that, and the puck saturates 3-4 seconds sooner. I'm not convinced that water contact with the top of the puck is a better measure of grinds saturation than the middle, or the bottom.
Jim's approach (half the dwell time plus all the pour time
) is a reasonable compromise. If nothing else, it cuts the variance between different ways of timing in half.