A perfect shot always has a “double mousetail” of extremely thin (less than 1/8″) espresso flowing from the portafilter for the duration of the shot. If this stream widens or pales, the shot is spent and bitterness is flowing into the cup. Conversely, if only a few drops come out and large oil bubbles form, the puck is packed too tightly and grounds are too fine, resulting in an extremely sour shot with little to no crema.

Differences in ambient air temperature, barometric pressure, humidity, and the nature of the beans themselves (is it a blend or a single-origin, wet-process or dry-process or some combination thereof, roasted into second crack?) can all make it difficult or even impossible to pull drinkable shots, even if exceptional equipment is being used. Using coffee beans that are a day fresh out of the roaster results in fizzy, nasty, sour, acrid espresso. Use beans that are a month old and the espresso will be flat and dull.

Timing is highly dependent on these other variables. A single-origin dry process espresso roasted just to second crack, ground to a fine degree, and updosed will produce a beautiful ristretto that might take 30-35 seconds to fully pour. Conversely a French-roasted Southern Italy wet-process bean might pull in just 18-20 seconds. If your barometric pressure drops dramatically and you’re using a HX machine, be prepared for perpetually awful shots as the boiling point and pressure calibration get completely messed up, resulting in sour low-temp bubbly extraction. Not giving beans time to depressurize after they’ve been stored in a sealed jar or tin container (a la Illy) will result in fizzy sourness as well.

FYI, I’m a diehard coffee drinker