although interesting
it misses a very important point.
@weinoo as mentioned above.
they do mention a few good points though
but Ive found , if you are using a ' bottom-less ' portafilter '
https://www.youtube.com/watch?v=lqD_tnqtJiM
the thickness of the steam will tell you instantly how your extraction is going.
and w a very good grinder , one that can take very very very fine adjustments
one needs to adjust each days grind for the same coffee in the hopper
to get the ideal stream and thus optimal espresso.
very odd , but very true. the beans change day to day , over several days.
and the grind needs to adjusted accordingly .
if the steam is too thin , the coffee is over-extracted and bitter
if the stream is too wide , is under-extracted and thus not full flavored or full bodied.
channeling is when the ' puck ' is not uniform and coffee works its way
vis least resistance and can spray all over the place.
