Gratuitous photograph of Millie our golden retriever puppy...
I wanted to step away from hyper technical coffee concepts and equipment and go back to a more fundamental concept... that of optimising certain variables so that you best enjoy your espresso. The two most controllable variables are grind size and dosage (the amount of coffee you load into your portafilter basket). These two variables have a direct impact on the amount of time the hot water takes to be pushed through your coffee grounds.
The key concept here is that coffee extraction is directly related to the amount of time it takes for your machine to make your coffee. If your coffee is over extracted (the key thing you'll notice is that it is bitter) then it's taking too much time to optimally extract. You can do either or both of (1) make the grind more coarse and/or (2) reduce the dosage of coffee in the portafilter.
Conversely, if your coffee is under extracted (it's sour) then the extraction time is not long enough. You can do either or both of (1) make the grind finer and/or (2) increase the dosage of coffee in the portafilter.
Hope that is helpful. As a heads up I'm going to be comparing pre-ground coffee and grind on demand coffee each morning over the next week and will let you know what I think in the next newsletter.
To read about latte art click here
To learn about coffee bags click here
To hear about coffee produced by Guatemalan women click here