Espresso machine styles - the single boiler

I am continuing my series on why I think Heat Exchangers are such a great deal in spite of being absurdly expensive, but we have had enough talk about heat exchangers without talking about what the various types of machines actually are.  There are two obvious ways to make an espresso machine.  This is a third way and to my view an amazingly clever one and simultaneously a simple one. 

The first obvious way is to have a single boiler for espresso and steam.  The natural problem is that espresso must be pulled below 212 degrees that you have for boiling water that is necessary to create steam.  The solution is reasonable enough.  You have a boiler that is kept at lower temperatures until you are done making espresso and then you raise its temperature until it is the right temperature for steam.  If you want to make a latte, you have to decide if you want to make the espresso first or the milk first.  This is not a catastrophe although once you aspire to latte art, you realize that great microfoam waits for no man (nor for any shot of espresso) so you are compelled to pull the espresso first.  Now this still is not a catastrophe, because although you need crema to produce great latte art, the hyperbole around needing to have the shot just pulled is exactly that.  You can pour good art a little after pulling the shot, so you can afford to wait if you need to.

So the biggest knock on the single boiler is that you have to wait and that it is a bit of a pain.  The next knock, is, of course, that if you want to make several milk drinks you may be in trouble.  You have to pull your shot and then steam and then wait for things to cool off and then pull your shot and then steam and then wait again and the cycle can get to be a major drag at a dinner party.  This is not too bad for me because I don’t tend to drink coffee late at night, but when family visits then I get frustrated.  Next up is the idea of a double boiler.