Dose. It come down to how the grinds exit your grinder and enter your portafilter. You move your portafilter around to make sure all empty space is filled and the coffee lands evenly in the portafilter. In essence, you slightly overfill to make sure all crevices below the lip of the basket are filled. You can Schomer it NSEW with a finger, Stockfleth it in a circle with you palm, or you can Schyndel(I can make my own up right?) it. I prefer to pinch the coffee using a scissor(index and middle finger) move on the surface of the basket and then swirl or go NSEW compensating for the deficiency of grounds in the basket. The idea is to let the lightly pinched coffee fall gently into the areas of lower density but in no way should you be pushing the coffee down. Seriously though, you could lid scrape NSEW or whatever variance works for you. The important thing is to use the right basket for your dose.
Yes, I said it, use the right basket for the gram dose weight you wish to attain. Dose volumetrically. Whatever gram dose you want, you need the right basket for that dose. That means when you run a lab or multiple coffees, you need an assortment of baskets that you can move through to find the right dose. 14g 16g 18g 22g, these are all different baskets. Try it and really think about it. If you use the right basket, all you have to do is level it with no fancy moves every time and you get the right dose. If you underdose/overdose a basket, you lose consistency. Consistency which is one of the most important things behind the bar(reduce all variables for repeatability). Break out your gram scale and see how consistent your shots are trying to over/under your dose every time.
When it really comes down to it, baskets are designed for volumetric dosing and you really can't break out the scale for every shot in a cafe setting. Have that scale handy so you can 'compare apples to apples' but when it comes down to it, you got to use the right basket. Your pucks will be beautiful and have room for proper expansion without crushing the screen or being a soupy mess.
-Jaime
