GRIND IS CRITICAL
The ideal grind will result in a slow, steady flow of espresso into the cup.
It it’s too coarse, the espresso will gush out, thin and under extracted.
Too fine, it will drip out, one bitter drop at a time.
For lower-pressure units, an extra-fine grind with some granularity will work well.
A inexpensive blade grinder can provide the appropriate texture.
High-pressure, commercial-quality units require a finer, more powdery grind. This is most easily obtained from a specialized burr-type grinder.