Time
The fastest espresso recipe you will find anywhere would take 15 seconds from turning the button on up until the moment the shot finishes. The slowest recipe might take 45 seconds. Baristas can manipulate how long it takes to produce an espresso by grinding beans finer (into smaller particles) or coarser (into larger particles).
The Relationship Between Time and Grind
The word resistance explains how shot times and grind settings interact. If you didn’t grind the coffee at all and then you made an espresso using whole beans, all the water would come through in about 5 seconds. This is because the water could easily fit through the large gaps between beans. In this situation you would have zero resistance to the flow of water. Then again, if you ground your beans on the finest possible setting, it could take as long as 10 minutes for your shot to finish. The gaps between each particle would be tiny and therefore much more difficult for the water to squeeze through. This would indicate too much resistance.
This gif demonstrate the extreme of grinding too coarse by brewing whole beans. You can see there is no resistance to the flow of water at all.
Somewhere in-between those two extremes is the ‘sweet spot’ where you have the right amount of resistance from the grinds to hit your recipe’s shot time target. Your challenge is to stay in this sweet spot for every customer.
The Margin of Error for Time
Working as a barista in a busy cafe environment is like driving a car in heavy traffic. You need to be alert to unexpected changes to your shot times. A recipe may call for a 30 ± 2-second shot time. Some cafes need you to be absolutely accurate, and they promise their customers great consistency and quality.