Would 18 grams of espresso pulled in a 18 gram basket taste diffeerent than 18 grams in either a 20 or 15 gram basket? If they would why is that. In my mind, as long as the baskets are equal diameter, the coffee puck would be identical. The only difference I see would be the distance from the top of the coffee to the dispersion screen. Why would that change flavor?

Don't forget, the grind size would be different too and that I think affects the flavor more than the basket's shape..Just my 2 cents..

I think the OP meant to ask if all other factors stay the same, ie, same grind same dose, but going into a different basket.

Two things:

First, you do get a sort of preinfusion if you use a larger basket. That is, with a bigger basket, there is more dead space (air) above the puck that needs to be filled first before the pressure ramps up, so there will be more time for the top of the puck to be hit with unpressurized water before the portafilter basket is pressurized. In terms of how much of a taste difference it actually makes, the difference in volume between a 15 and 20 gram basket is pretty darn small so I wouldn't think it would be that significant, but I know other folks have suggested it.

Second, if you overdose too much and your puck ends up hitting the dispersion screen you could mess up the flat surface of the puck and be more likely to get an uneven extraction.

Wrong question. It's grind and shot time that determine the taste. If you use the same dose in diffferent baskets and change the grind; it won't taste the same. If you use the same dose and grind, and it chokes or gushes, it won't taste the same.

What if he uses 18g grounds in an 18g basket. With no errors or defects in this shot.

Same 18g, nothing changes, in a 20g basket.

Same 18g, nothing changes, in a 22 g basket.

Try it. You'll have hard time achieving "nothing changes"

The missing info might be in this thread discussing filter baskets. The short version is that different baskets are "designed" for different doses by changing the geometry and flow characteristics (size, number of holes).

Think of the difference between a single and a double, rather than 18 or 20g.

Are you saying that either hole sizes change or # of holes changes?

I dont notice much if any difference between basket brands of the same size. Have not tried putting 18 grams in a double then the same 18 in a triple basket. I would surmise that as long as the shot did not melt down from all the added headspace, you would get very little to no change beyond your normal shot to shot variance.