The previous video on Buying Advice discussed double boiler espresso machines, but largely skipped over heat exchangers (HX). As part of their buying decision, a shopper is confronted with lots of choices, but frequently doesn't know how these two types of espresso machines differ. This video explains how HX espresso machines work and how its design affects the barista's routine. The video ends with a side-by-side taste test.
Below is the HX hydraulics diagram by Eric Svendson and Lino Verna that I used in the video. If you're interested in the E61 thermometer adapter I mentioned in the video, please contact Eric directly via e-mail or PM. The shorthand terms for HX espresso machine characteristics that I mentioned in the video are described in more detail in the thread Ideal brew temperature management by HX espresso machine type.



The earlier segments of the series are linked in the main thread, Espresso 101: Newbie Introduction to Espresso.

Pour time is possibly a minor contributing factor, but the taste difference was easily reproducible. Before we started the camera, I pulled two doubles for myself and Phillip handed me each at random to confirm I could discern the difference (and yes, I kept my eyes closed). To me, it was obvious which was which by taste, so I figured he'd have little trouble spotting the difference when the camera was rolling. Fortunately, he guessed correctly.

I calibrated the brew pressure with a Scace II portafilter. The brew temperatures are harder to compare meaningfully when one profile is flat and the other is humped/declining, so I set them to be equal around the 20 second mark. Both espresso machines were backflushed within the last few days, though honestly I would spot the taste defect associated with a dirty grouphead right off.

I intentionally chose an espresso blend that has noticeable fruit flavors in the background (Rustico by Counter Culture Coffee), hoping that it would elicit a difference between the two espresso machines. Before I wrap up the reviews, I'll try side-by-side comparisons with a variety of blends in a group setting.

damonbowe wrote:Were the machines flushed prior to use and were the group heads at about the same temperature based on Eric's thermometer reading before you pulled the shots? I'm still not clear on why there would be a difference in these shots if the groups are showing approximately the same temp before pulling and the machines are both fully flushed.

I have been working on the Izzo Alex Duetto V3 Review for the last couple months and the ECM Technika IV Review for the last couple weeks; to the best of my abilities, the two espresso machines were dialed in similarly. The Technika doesn't have Eric's grouphead thermometer installed. I'll install it at some point in the review, but I prefer to start the research section of a review with the equipment as-shipped. As for the taste difference, I speculate that it's due to the hump/declining brew temperature profile (HX) versus flat brew temperature profile (double boiler).

damonbowe wrote:I don't know if it's because I'm OCD or whatever, but I immediately started to become nervous about the time period of the grinds sitting on the counter and no showing of group flushing in the video!

I'm betting on the former. The video had a cut while we setup for the taste test, so prep steps like dosing and flushing were not shown. Actually, that was the second take since one of the machines ran out of water mid-shot. D'oh!