Espresso: grouphead water temperature analysis
I’ve had the joy of a beautiful espresso machine (Kim Express) for years, and I learned through trial and error just the right time to pull the best espresso shot. Lately though, as a result of using la Pavoni and Flair Espresso more, I’ve come to appreciate 90C (194F) as the aim for water and machine temperature. So I’ve done a little experimenting to understand how quickly water cools in a Flair Espresso machine.
For la Pavoni, I didn’t use it often enough until this Christmas to refine the shot. I thought it would be straight forward, but unlike the Kim, the clues that the machine was ready were more elusive. The slight difference in design meant that for la Pavoni, you had to release the false pressure and preheat the grouphead before pulling a shot, unlike the Kim. The Kim Express has a release valve that bleeds off the false pressure, and because the grouphead is more physically connected and closer to the heat element, it’s at the same temperature as the machine.
For Flair Espresso, I could pull a good shot, but it was still a couple levels lower quality than what I could on other manual machines like the Kim Express. I did preheat the grouphead, but I didn’t feel confident it was the right temperature. The main indicator was taste. The shot didn’t have the sharp richness as on my other machines.
There are three ways most Flair users preheat the grouphead: full immersion (Flair’s recommendation), steam, and filling the grouphead with hot water (my preference). Full immersion requires getting the element out of boiling water, which is why I was working on filling just the element with the plunger inserted.
I first noticed an issue with the taste. I adjusted grinds and brew times, but I was unable to get quite the same sharp richness I could from the Kim. During Christmas break, I was using la Pavoni and Kompresso, and between the two machines, water temperature became the main variable I was chasing down to get that good ole syrup espresso shot. During this process, I could taste the flavor getting sharper and richer as I controlled a high temperature during the brew. When I returned home and used Flair again, the answer was clear: I needed better temperature management.
So, I did what any data scientist would do: I collected some data. I wanted to know with the method I used, how quickly did the temperature drop? If quickly, how many cycles of boiling water would allow the water temperature during brew to stay above 194 F?
I setup a camera, and I took a video of a thermometer over multiple cycles. Any cycle could be considered how the water temperature would change while brewing a shot, so successive cycles would show the effects of pre-heating the element.
The only caveat is that the top of the grouphead remained open, and normally the filter is there. So this analysis is truly the worst case temperature drop. To note, the room temperature was 70 F with the shades drawn. The water was at a rolling boiling for each cycle using a pot of boiling water.
As for the temperature measurement, the temperature probe often times had to get to temperature which delayed when I got the peak temperature. I interpolated between the first good measurement and 212F because the water should always be cooling down. The key was really answering the question of water temperature with respect to espresso brew times hence the timing bars at the bottom showing pre-infusion, starting to push down on the filter until coffee starts to come out, and then the final push.
Based on this test, doing a single pre-heat cycle will cause the water during the shot to drop below the ideal 194F or 90C. What if we do a few more cycles? The graph below shows two pre-heat cycles will do the trick, so the third would keep the temperature for the duration of the shot.
What about pre-heating by submersing it in a cup of boiling water? It seems like that solution works better than a two rinses of hot water.
What about Kompresso? Kompresso is even more portable than Flair. It is made of plastic, so I was curious how well it insulated heat. One issue is that Kompresso can not be pre-heated easily. Looking at pouring boiling water into Kompresso, it seems to hold temperature until the end of the shot.
The one caveat is that the plunger is on top of the device meaning some more heat could be escaping, so this information is really the worst case. That being said, it requires boiling water. Water at a lower starting temperature would probably fall below the desired temperature before the end of the shot.
Ultimately, an espresso machine with a heated element can maintain the same temperature throughout the shot whereas Flair or Kompresso will have the water temperature change throughout the process. There is definitely a difference in flavor and look. Here is my score sheet for the two. Lower score is better; 0 is the best, 2 is the worst. They are similar to face recognition scores signifying closeness to desired, so 0 means that’s the desired taste.
