So long as it's a good evenly extracted shot with balanced flavor, the time does not really matter. Even if training for competition, the WBC score sheets deduct only a minimal point value for extractions outside of the so-called ideal 20 - 30 seconds; by contrast, taste is much more heavily weighted.
At your business or in a competition, tasting good is far more important that being within some theoretical time parameters.
Focus on the flavor first; if that's off balance, then go back to review the technical standards like timing.
I agree partially with Andrew... the 20-30 second range is a good starting point, but part of dialing in your espresso is narrowing this down to a better (read narrower target). That said, once you've established that target, consistency between baristas on your bar staff is important. I personally start timing when the first drops fall from the spouts, but have no valid reason for doing this.
One thing that I have never found a "definitive" answer for is the time for a dopio. I am assuming that using a double basket, I should be looking for times between 40-50 sec?
I dropped math at functions statistics and trig my senior year to take Spanish four so the calculus here is a bit beyond me. Illy says that p represents the difference in pressure above and below the puck, R is the hydraulic resistance of the cake, V is the volume of the beverage, T is the temp inside the cake, and t is the percolation time (I'm not sure if that is the full extraction time of the time to first drop). Illy doesn't define the d at the end of the expression, but I assume it is the mass of the cake, because it would have to figure in there somehow right?
which appeared in my expression.
You should always be shooting for 25ish seconds, regardless of whether you are using a single or a double or a triple basket, whether you are pulling a ristretto or a lungo. It has to do with volume, not time.
-bry Chris Hooton said:One thing that I have never found a "definitive" answer for is the time for a dopio. I am assuming that using a double basket, I should be looking for times between 40-50 sec?
I think I am getting my head around what you are saying. So long as the volume of the finished cup and the mass of the ground coffee increase proportionally then the time stays the same. So it could be expressed something like this:
Where d is the mass of the ground coffee in grams, V is the volume of water in ml and the time of the shot in seconds and R some crazy constant representing the rate of extraction.
Thanks Brady, that helps make sense of this for me.