Heat Exchange vs. Double Boiler

We admit it, we're guilty. We thought that size did matter with regard to boilers on a semi-automatic espresso machine -- namely, that two boilers was better than one. The hierarchy in our mind was:

  1. Single Boiler: From the Saeco Aroma to the Rancilio Silvia, the single boiler is a great little semi-automatic espresso machine that requires special attention to boiler temperature so that you're brewing well below the steaming temp and not burning your espresso. With a single boiler, you're not able to brew and steam at the same time -- we recommend steaming first, then brewing.
  2. Heat Exchange: Instead of pulling your brewing and steaming water from the same vat, per se, heat exchangers like the Rocket Giotto Premium Plus or Quick Mill Andreja Premium transports fresh water from the reservoir through the boiler via a copper tube that is specifically designed in length and girth to heat the passing water to the optimum brewing temperature, not the steaming temperature. We are talking about a nearly 40F degree difference, so this improved temperature regulation significantly upgrades the espresso shot quality. This functionality also allows for simultaneous brew and steam.
  3. Double Boiler: Only a few models on the market, such as the La Spaziale Mini Vivaldi or Izzo Alex Duetto, feature absolutely separate boilers for steaming and brewing, which allows you to maintain disparate temperatures and brewing and steaming at the same time. You can generally program your preferred brew boiler temperature on these machines and, in the home espresso machine space, they generally feature a quicker recovery time than their heat exchange counterparts.

So, based on those assessments, you'd understand why we were confused by the more is better idea -- that maintaining temperature is significantly easier when you've got two separate boilers doing their own thing.

However, in our recent research and education around the new line of commercial Faema machines we're now carrying, we learned that our hierarchical view was incorrect -- in fact, Italians haven't been using double boiler technology for decades, believing that the heat exchange technology provides for significantly improved espresso due to one major reason: It's alive!

Boiler water is considered 'dead' water because it's sitting in a little metal unit cooking away. Over time, this results in a significantly increased alkaline content in the water (ah yes, that lovely scale we keep talking about so much) and a mineral imbalance in extraction. Basically, the flavor's different.

Since heat exchange machines are continuously cycling fresh water through their siphoning system, they have an improved mineral balance and cannot become stale like the water in the double boilers might. So the flavor is significantly better and, therefore, preferred by connoisseurs the world over.

If you're in the market for a 'prosumer' machine, this is definitely important information for you to mull over. Not only is the footprint smaller on a heat exchange machine vs. a double boiler, but it just might pull a better shot.

8 thoughts on “Heat Exchange vs. Double Boiler”

  • Johan

    Hi Kat,

    I love the video's you an Gail do. Very informative indeed. As far as I know there nothing like that ou there.

    This is very interesting. Now, you mentioned 'research'. Have you guys actually experienced this phenomenon with the double boilers?
    I'm in the middle of researching my next espresso machine. Previously I owned a Miss Sylvia and current I have a Delonghi Magnifica. I want to go back to semi-automatic again because I like the whole process and the control it gives me. I'd like to have a machine that allows me to do latte art which I could not achieve with either of the machines I mentioned (no microfoam). So I did research and thought that dual boilers is the way to go. I make two cappunico's in the morning and in the evening, on the weekends a bit more. I like the ones that have temperature control (PID or otherwise) and would also like to be able to pull a shot and foam at the same time. What kind of machine would you recommend? Double boiler or heat exchanger?



    • victor

      There are pluses and minuses either way. A double boiler machine gives you more options and often more power for steaming (depending on the model). They typically include a temperature controller (PID) that allows you to dial in precisely the brewing temperature. On the down side, if you are just pulling a few shots a day then you are typically using the water that has been sitting in the brew boiler. If this was used in a more commercial environment, the volume of shots would assure this brewing water was always fresh. For home use, you could rinse this out before brewing. The heat exchanger machines are designed to deal with this problem, since brewing water travels directly from the fresh water reservoir through copper tubing to the brew head. In our view this produces a 'fresher' tasting shot of espresso when using the machines at home for '1 or 2' shots a day. The Heat exchangers have large steaming boilers so typically steam as well as double boiler models at home.

  • [...] This post was mentioned on Twitter by Caroline G. Caroline G said: Can someone answer this one...which is better...heat exchange or double boiler? http://bit.ly/c0YaKb [...]

  • […] want a double boiler for consistency. We’ve dived into the differences in a past post you can check out here, but the gist is that heat exchangers are continually siphoning fresh water to brew while double […]

  • […] machines the San Marcos for example are designed to make 100s of short blacks per day. The heat exchange system works in a culture where 9 out of 10 coffees are […]

  • […] machines the San Marcos for example are designed to make 100s of short blacks per day. The heat exchange system works in a culture where 9 out of 10 coffees are […]

  • […] you’re looking to steam and brew, you might look for a dual boiler machine. This uses independent boilers that enable you to steam milk and brew coffee at the same time (although they tend to be more […]

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