Hi everyone, I have a really annoying problem with my Barista Express.

I got the machine some 3 months ago, and I leant to dial in the grinder and distribute the ground and stuff. The first cup in the morning is always great, 19.5g dose, 30-34s and yields 38.5g (or as the beans gets slightly older, 19.5g dose, 30s extraction and yields 42g). BTW, I can't seem to get 19g 30s 38g, as one notch down or up in the grinder will either over extract or the other way around.This is the closest I can get.

The problem comes with the second cup. After the perfectly fine first cup, despite no changes in any settings, in the second shot, I can often observe either a drop in extraction pressure, consequently shorter time and more yield; or higher pressure to the point that coffee comes out 40+ seconds I didn't even bother to weigh the shot.

To give more context and details, here's how it happened today, as an example:

1. Wash and wipe dry my portafilter with paper towel. Since it's the first cup in the morning the basket is usually dry, so this step is skipped.
2. Tare portafilter on scale, then grind into basket, knock on the counter to make the ground collapse a bit, then use OCD to distribute and tamp with tamper came with the machine. Measure dose 19.5g.
3. Run single shot without portafilter on to purge group head.
4. Tare the cup and run the shot. Grind size 7, pressure stables around the last gradation within the espresso range (*not the gradation on the edge of the range). Dose 19.5g, 31s, 40g
5. Steam milk.
6. and repeat from step 1, then see the pressure goes beyond the espresso range, over extracting.
7. adjust grind size to 8, purge grinder with double shot timer.
8. repeat 1-4 and pressure at first gradation within the espresso range (also, not the one on the edge of the range), extraction took 28s, yields 45g, espresso tasted sour.
9. Adjusted grind to 6, purge, repeat 1-4, everything backed to normal, 19.5g, 34s, 38.5g.

Does anyone know what is happening with my machine? Or this is the "inconsistency in cheaper machines" that would just happen?

Thanks in advance!!

I believe what is happening is that your first shot contains stale grinds from yesterday's session in it. The chute between the burrs of your grinder and the dosing mechanism holds somewhere between 5 and 8 grams. That's ~30-40% of your dose weight that lags behind any changes in grind (hence going too tight and then too coarse, before settling on just right).

Best practice would be to understand how much retention you have and then purge that out at the beginning of each session. This is very wasteful, which is one of the primary reasons I started single dosing and clearing the chute every shot on my Super Jolly. Unfortunately, the built in grinder on the Barista Express does not lend itself well to this strategy so you're left with variation or waste.

The easiest way to determine how much is sticking around is to empty your hopper and grind until nothing comes out the chute anymore and then switch to a much lighter or darker roast, something you can see the difference in the grinds. Then grind the new beans until you see the new color come out the chute. Measure all the old color grinds. This is your retention. Purge this amount out at the start of your sessions and consistency will be found.

Cheers!

- Jake