MattH Right — I cool the 9Barista under cold water, and streamline the process by starting the water heating process for the second shot, and then grinding and putting the top on while the water is heating up.
I once timed myself doing back-to-back shots with the 9Barista. I wasn’t rushing to set a record — I wanted to see what the real-world experience would be.
After pouring the first espresso, I started my stopwatch. I went to the sink and ran cold water over the 9Barista until it was cool enough to take apart the three sections. I released the safety valve, rinsed out the bottom and middle sections, and dried them off with a towel. I filled the bottom reservoir with water, screwed the middle section on, put it on the stove, and turned the heat on.
While the water for the second espresso was heating up, I popped the basket out of the top section, took the puck screen out, and knocked the puck out. I cleaned the top part, the basket, and the puck screen, and dried them off with a towel.
Then I measured out the coffee beans for the second shot and ground them, I filled the basket, tamped, put the puck screen on, and attached the top part to the middle and bottom sections that were on the stove.
At this point my stopwatch was at 5 minutes 24 seconds. I was close to when the water would be boiling, as I could see bubbles under the top of the middle section as I was attaching the top section on. (This doesn’t always happen. Since I did this timed run, I have a new grinder that’s faster — 10 seconds instead of 35 seconds for grinding — and so I can get the top section on quicker. This won’t affect the total time for the back-to-back shot, just this part of the process.)
Espresso started coming out 17 seconds later. The extraction time was 29 seconds.
So the total time from starting to cool off the 9Barista right after pouring the first shot to finishing the extraction for the second shot was 6 minutes 10 seconds.
Given how close the water was to boiling when I attached the top section to the middle and bottom sections, my sense is that the main bottleneck from one shot to the next is the time it takes for the water to heat up. So washing out the middle and bottom sections first, and then getting a headstart on heating the water for the second shot is a really good move.
In my experience, the workflow for doing back-to-back shots is pretty straightforward, and if you do this on a regular basis, I think anyone can get it down to 6-½ minutes or less.