Single boiler, double boiler, heat exchanger… They’re all names for different types of espresso machines, but what do they actually mean? And why do we even need different types of boilers?
The answer all boils down to the difference between the temperature for frothing milk and extracting coffee. Since steam mode requires the water to be hotter, each espresso machine needs to have two different ways to produce hot water.
This means that a single boiler machine has a button to switch modes, and you have to flick it between them – and you don’t want to forget, because you’ll end up with a pretty unpleasant coffee. Double boilers, on the other hand, are self-explanatory and fool-proof: one boiler for steaming, the other for the espresso. They also tend to be a lot more expensive.
The one that can confuse people, however, is the heat exchanger boiler. It has one boiler, but you don’t need to flick a switch to change the temperature. Instead, the boiler is kept at the steam temperature but also has a thin tube inside it. Cold water goes through that tube, almost instantly heating up to espresso temperature, whenever you need to pull a shot of espresso.
Is this confusing? Watch this short and sweet video from Whole Latte Love, in which they saw open a heat exchanger boiler to give a visual representation.
To recap, the main part of the boiler – the part with the heating element – is where the water is heated for frothing milk. The tube going through the boiler is what the cold water goes through, before it emerges at the perfect temperature for extracting coffee.
Please note: Perfect Daily Grind does not own the rights to these videos and cannot be held accountable for their content.