Petals cherie -- not everyone is a barista. Be of good cheer, you whip my behind in desserts.
A heat exchanger espresso machine heats the brewing water in a hollow coil in the boiler (which holds steam and water for steaming and Americanos). The coil is the actual "heat exchanger," and it draws its heat from the boiler which is usually heated by an electric element and that's usually controlled by a "pressurestat."
Because the steamer is kept hotter than the correct brew temperature to make steam, if the machine isn't used for awhile, the water in the heat exchanger equlibriates at the boiler temp which is too hot for brewing. The overly-hot water must be drained, so fresh water can come in and be heated to the appropriate temperature. The water is so hot, it comes out as mixture of steam and water and jumps around as though it were dancing. That's called the "water dance."
Most commercial grinders have a "dosatore," which dispenses the ground coffee into the coffe holder (aka porrofilter). It does it by rotating a disc with a hole in it. When the hole in the disc lines up with the dispensing spout's hole, coffee comes out. But because the disc is rotating it spins the coffee clockwise. That is, it puts "left English" on the grounds. So the coffee mounds up higher on the left in the porrofilter. Before compressing it (tamping) to make the "puck," the barista taps the porrofilter against her right palm to center the top of the mound.
Fraicheur, n'est pas?
I really like that question, because it stumped the guys over at Home Barista for months. They kept trying to come up with intelligent, engineer type reasons; instead of the prosaically practical. While I didn't raise the question, I didn't answer it either. The bizarre hypotheses were just too wonderful.
When stripping the membrane off the back of a raw rack of ribs, what's the best non-slip tool for holding it?