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For an updated look at boiler designs, check out our new blog on the topic.
So you’ve been thinking about purchasing a semi-automatic espresso machine for home use. You start your research and boom! Out come a number of acronyms that don’t make sense to a newbie. If you haven’t seen them yet, you will. The main ones are SBDU, HX and DB. Those acronyms refer to the boiler or boilers in the machine.
SBDU machines use a single boiler to produce both brew water for the espresso and steam for frothing milk. They are usually less expensive than the other types, and have a big limitation, in that, they cannot brew espresso and steam milk at the same time. Two good examples of SBDU machines are the Gaggia Classic Pro and the Rancilio Silvia.
The big limitation with SBDU machines is their inability to brew and steam at the same time, and the waiting for the machine to get up to steam temperature after brewing. Getting up to steam temperature on an SBDU could take as long as 2 minutes. If you’re making multiple milk-based drinks, all that waiting adds up. Plus, it’s not just about having to wait for the steam to come up to temp, you also have to wait for the boiler to cool down after steaming before pulling another espresso.
HX machines use a single boiler but can brew and steam at the same time. To have this capability, the boiler is always kept at steaming temperature. Brew water travels through the same boiler in a separate system and is heated to a lower temperature. Manufacturers may implement heat exchange boilers in different ways. For example, Expobar uses a vertical heat exchanger, whereasProfitec favors a horizontal design.
On HX machines, experienced users can learn to manipulate brew temperatures with timed flushes of overheated water contained within the heat exchanger. Some users like that capability, and, well, some just like the lower price compared to a dual boiler machine.
DB machines use two boilers, each with its own heating element. Like the heat exchange machine brewing and steaming can take place at the same time. Dual boiler systems may be implemented differently based on the manufacturer. The Rocket Espresso R58 uses two independently heated boilers, while the Breville Oracle Touchuses its steam boiler to preheat the water in its brew circuit.
With HX and DB machines both able to brew and steam at the same time what’s the difference? Well, there are a few. A major one: brew temperature. Though it’s difficult to quickly manipulate brew temperatures, dual boilers are very consistent in comparison to heat exchange machines.