In our last post, we tested various espresso brewing temperatures and their influence on taste. Here we show you how and where the espresso brewing temperature is measured, and how you can measure the temperature of your machine at home.
The perfect brewing temperature for espresso is between 91° and 95°. For a darker roast, we recommend the spectrum of 91° to 93°. For lighter roasts, we recommend 93° to 95° espresso brewing temperature.
Try this at home and set different brewing temperatures to check sensorially what tastes best to you personally. But the question here is exactly where we measure, and just how precise the whole thing is.
Espresso and brewing temperature – plenty to discuss
Since I've been dealing with coffee, brewing temperature has always been worth a long conversation. Different brewing systems and group head designs significantly change the consistency and impact of temperature. As a result, there often lacks clear information about what spectrum the optimal brewing temperature lies in.
Despite this, or precisely because of it, we've taken on this topic and first examined the sensory changes and strength or extraction. Rightfully, questions followed in the blog and in the comments on the YouTube video:
- where do you measure the temperature?
- how consistent is such a machine?
- how precise are these measurements?
To answer these questions, we first need to understand the design of boilers and group heads and their impact on temperature.
Espresso brewing temperature in thermobloc machines
A thermobloc heats water as it flows through a tube within the block. This means that with small thermobloc systems, the inlet temperature is crucial.
Fresh tap water is usually cooler than water that has been sitting in the machine tank longer and has assumed the ambient temperature. The two water temperatures are different and need to be heated for different lengths of time. Thus, in this case we end up with different brewing temperatures again.
We recommend always using fresh water to keep the starting conditions constant. The larger the thermobloc, the fewer fluctuations you can expect. With sophisticated systems, as we see with the Decent Espresso Machine, the thermobloc performs more consistently than a boiler system. This works because the group head is preheated by an additional heater and numerous temperature sensors control the water supply.
With the thermobloc, measurement is done with a thermostat that often switches on and off in the 5-6 degree range. So it might start heating at 104°C and stop at 110°C, for example. Temperature fluctuations can also occur here.
The temperature measured this way is the temperature in the block and not the actual brewing temperature. Depending on the design, this is then between 87°C and 93°C.
Caution – too cold brewing temperature with the thermobloc if…
if the group flushes shortly before extraction. Because: before extraction, the thermobloc stays at approx. 104°C. If you start the extraction and the boiler heater switches on at that moment, you'll start the extraction at approx. 87°C and finish rather too hot. That's why we recommend flushing thermobloc machines immediately after removing the portafilter and thus before grinding, so the thermobloc can heat up again. Thermobloc machines are generally rather too cold than too hot.
Procedure for brewing with thermobloc machines
- Remove the portafilter
- Flush the group briefly, short water draw
- grind and fill the portafilter
- extract
After step two, the thermobloc heats up quickly and you achieve the higher brewing temperature.
Thermostat and pressostat instead of PID
With almost all boiler machines without temperature control (PID), the temperature is regulated by a mechanical thermostat or pressostat.
The thermostat
Let's start with the thermostat, as this is rather rare and usually found in cheaper machines. As soon as the boiler cools down slightly, it signals the heater to heat again. Since a boiler basically has much more water than a thermobloc, boiler machines are significantly more consistent in temperature. The thermostat also regulates the temperature in approximately the 5 degree range.
The pressostat
Slightly more precise, and therefore also installed in most dual boiler machines without PID, is the pressostat. It also sends the heating signal to the heater, but regulates this via pressure. With both methods, measurement is done in the steam section of the boiler.
With a built-in boiler of usually 1.5 to 1.8 liters capacity, the temperature fluctuates somewhat with both systems. With the functioning of a so-called heat exchanger, the immersed cylinder in a classic dual boiler, the temperature fluctuations stay within limits. Adequate flushing before brewing also helps here to reduce the temperature of the thermo-siphon system (design of a Faema E61 group head, in which water circulates permanently) before the group head, so as not to extract the coffee with too hot a temperature, making it more bitter than it actually is.
Here too, the principle applies: the larger the boiler, the more consistency. With a 3-liter boiler, there is much more water that loses significantly less temperature during extraction. Also in the moment when the pump pumps cold water from the water tank into the heat exchanger. The results in the cup are thus much more consistent. With the Basilea with PID and a 3-liter boiler, we measured a temperature fluctuation of less than 0.4 degrees – this is world championship level!
Where do we measure on machines with temperature control?
There are major differences between dual boilers with PID and dual or multi-boilers. How these machines are designed and how they work, we discussed in detail in this post.
Dual boiler with PID
Let's take the next step in the price segment and move to dual boilers with PID. Now we no longer measure mechanically via pressostat or thermostat, but via a sensor. This allows precise measurement and precise control of the heater. Often, heating systems in dual boilers without PID either heat fully or not at all. As soon as a sensor is installed, the heater in the boiler keeps the temperature more constant, either through full heating or targeted heating pulses.
Measuring PID correctly
Measurement is then done in the steam section. Therefore, with PID machines, you must always convert the displayed temperature according to the operating instructions.
An example: 124°C displayed boiler temperature can correspond to a brewing temperature of approx. 92.5°C. But always use the operating instructions of your machine, as this varies from manufacturer to manufacturer.
Even with PID devices, we recommend flushing directly before brewing, as the water can heat up very strongly in the brew head here as well, and you thus start the extraction with a very hot temperature.
Dual or multi-boiler
With luxury models with dual or multi-boilers, we measure separately in each boiler. This enables a very high steam temperature, independent of a differently set brewing temperature. But here too, the larger the boiler, especially the coffee boiler, the more consistently you'll be able to brew.
The new systems in the professional gastro sector go even a step further. To achieve consistency of less than 0.5 degree temperature fluctuation during brewing, today the group heads are actively heated to make them even more consistent. This ends up with a multi-boiler machine with two coffee boilers per group head and active boiler heating. Fluctuations are minimized to 0.1 to 0.2 °C and are thus negligible.
Measuring espresso brewing temperature at home
To measure the brewing temperature on your own machine, you need a temperature probe that you insert deep into a portafilter outlet. Then you start a draw without coffee – it's important that you always do this with a hot portafilter. There are also portafilters with built-in thermometers. We use these, for example, for our tests, as this also creates resistance against the pump.
If you want to take the measurement with coffee, the water naturally loses significant temperature at the beginning of the extraction, as the coffee is at ambient temperature in the portafilter. You'll notice a large increase during extraction.
But don't forget to drink your coffee while you're busy measuring.
