Roger Shoaf wrote:
I am thinking about making an espresso maker and one of the design
considerations is the ability to tightly control the temperature of the
water as it is forced through the coffee. It appears that one of the week
points of the current designs is the lack of thermal stability of the brew
head.

For your interest, some of the best quality espresso machines (e.g.,
Faema) use an electric pump to pressurise cold water, which is then fed
through a heat exchanger before it reaches the brew head. The water in
the boiler acts as a heat reservoir but doesn't actually end up in the
coffee. If you search for a history of the Faema company online you
should find more information. There was also a Faema dealer who had many
detailed pictures of Faema machine parts online, but I'm afraid I can't
remember the address right now.

I've always hankered after a Faema E 61, but can't afford it. Maybe one
day I will pick up a broken one and restore it.

Chris