domobar super, e61 thermometer, mazzer mini, home roasted beans, wdt distribution, I weigh my grinds, etc. My first pull is always eye popping and perfect. I am pretty sure nothing is changing for my second pull but often it flows a bit faster and lacks the telltale signs of a good shot on the crema surface. My 1st & 2nd pulls are also quite different in taste. The only thing I can think of is that i measure my beans (2 shots worth) and dump them in the mazzer.. maybe the 1st grind is finer since there is weight on the beans and the 2nd grind the beans are running out. Tomorrow I will try dumping all my beans in and then when finished tip them back in my container. Have I already found the problem? 2nd grind with loose beans in the hopper producing a different grind that pours faster?

Grind is a suspect to be sure. Try this: Grind both shots completely, then mix the ground coffee thoroughly and then dose the first shot from the mixed grounds.

ah, good idea!

jeffg wrote:Have I already found the problem? 2nd grind with loose beans in the hopper producing a different grind that pours faster?

Yes * 2.

If you grind until empty, the grounds are consistent shot-to-shot. As the chamber empties, the effective grind setting becomes coarser. This was noted during the Titan Grinder Project and has come up in threads like Leaving coffee beans in hopper and Is single dose [without hopper] grinding inconsistent? I have found this grind setting shift occurs on several grinders; as a guesstimate, the shift for the Mazzer grinders is equivalent to a 1 to 1-1/2 notch adjustment coarser. The new doserless Robur and Kony grinders claim to avoid this with the addition of an auger at the bottom of the hopper that provides downward pressure.

jeffg wrote: Have I already found the problem? 2nd grind with loose beans in the hopper producing a different grind that pours faster?

Let us know, but there are a coupla other things that could be contributing. Depending on the machine and your technique, it could be that you dose into a dry basket for the first, and the freshly rinsed one for the second. If the second set goes into a wet basket, it could be channeling? Or a combination of the two?
Let us know how it goes!