We distinguish between single-circuit machines for espresso preparation and dual-circuit machines for espresso and cappuccino preparation.
To prepare a cappuccino, you ideally need a 2-circuit machine, i.e. 2 separate brewing systems, one for the water, the other for the steam. This allows you to extract coffee and froth milk at the same time.
For mere espresso preparation, only 1 circuit is needed. (You can also foam milk with a single circuit machine, but you have to wait between coffee extraction and frothing until the temperature adjusts).
Another important component is a PID (electronic temperature control). Since "E61 brew groups" without PID like to overheat and coffee is known to taste very different at different temperatures, a PID is an advantage. Good machines offer this. So the temperature can be controlled to +/- 1 degree.
A tamper must necessarily meet the following characteristics:
- Exactly fit into the brewing sieve, maximum 0.2 mm clearance.
- Fit snugly in the hand.
- The tamper handle should be short enough for the fingers to touch the edge of the portafilter when it is in the palm of the hand.