Basics

A so-called Scace Espresso Machine Thermofilter can be used to determine temperature curves and the temperature stability of a machine.

The Scace thermofilter simulates the coffee through a plastic block that has similar thermal properties. However, you cannot measure real espresso extractions with a Scace, as the coffee crumbs will immediately clog the nozzle. Statements such as "my machine makes the best espresso shots at 93 °" can certainly not be made with a Scace.

For this reason, you must not use an espresso machine for measurement that still has traces of the real extractions somewhere. If in doubt, you have to remove the shower screen and painstakingly clean everything, ideally 1 hour before the start of the measurements.

However, you can check within certain limits whether the espresso machine remains stable under low or high loads and does not heat up or cool down. However, it is not enough to read off a degree at any given time. There is, however, a precisely defined measuring process that allows the temperature stability to be determined by a number at the end.

In order to carry out such a measurement you need some preparation and appropriate equipment: the Scace itself, two stopwatches, a data logger and ideally you film the measurement process for documentation.

 

The measurement

Die Messung mit einem Scace ist recht klar definiert (lässt aber einige Freiräume). Der Messablauf und die Auswertung ist hier definiert:

PROCEDURE FOR THE MEASUREMENT OF BREWING WATER TEMPERATURE IN ESPRESSO COFFEEMACHINES (2017)

And you can find a decent collection of evaluation results here:

Die Röster Freak-Artikel: Wir haben Temperatur-Präzision bei Espressomaschinen getestet

It is really worth reading through these explanations from our Austrian colleagues. Unfortunately, the article is available in German only.

Prepare the machine

When it comes to the reproducibility and comparability of the measurements, it is advisable to set up the espresso machine freely in a space that is not too small and to exclude environmental influences as far as possible. Above all, this includes: air drafts and high room temperatures.

Then you determine how long the espresso extraction time of the machine is to get 25ml of liquid per cup (50 ml in total). The length of an extraction (or the amount of liquid conveyed) has more or less influence on the temperature curves and, of course, on the comparability.

Machines with a timer make it easier to measure. Machines with manual start and end of the extraction (like a machine with an E61 group) make the measuring process a bit more demanding. An additional stop watch should therefore be used to record the extraction time (or its end respectively).

Preparation of the measurement

As described in the text above, the machine should be heated for 1 hour. This is a value at which every machine/ brew group will really have reached its temperature

Since you have to extract the measurements from the data logger file later, you should strictly adhere to the timing (including the pauses between extractions) specified in the document, because otherwise you will spend quite some time searching through the many measured values (apart from the fact that the comparability will be lost).

In order to get the measuring process right, it is best to use a table to tick off the individual steps, which is particularly helpful in the second half of the measuring cycle when it gets hectic because the temporal distances between the extractions will become very short.

If the starting points of the extraction times are already shown in the table, the work will become much easier. A stopwatch is used for this, which is started at the same time as the data logger. For example, if you start the first extraction after exactly 2 minutes, you can simply go by the stopwatch and the calculated times of the following extractions from there.

Nevertheless, it is advisable to write down the exact start time of each extraction, because you do not always hit the calculated point exactly and later it is difficult to recognise the correct values in the data pool.

 

 

You should fill the tank completely before taking the measurement and empty the drip tray, because you may not have time to make up for it later.

Da das Scace einen sehr feinen und scharfen Strahl erzeugt, legt man am Besten einen kleinen Schwamm in die Abtropfschale. Der reduziert sehr gut das Entstehen von feinem Nebel unter der Brühgruppe, der durchaus kühlend wirken kann.

 

Evaluation

A measurement cycle takes around 35 minutes and then you can evaluate the data from the data logger according to the definition.
In a spreadsheet such as Excel you can very quickly get an impression of the evenness (or unevenness) of the extractions, which is quite suitable for an initial assessment.
When comparing the 'peaks', you should not be able to detect any significant increases or decreases—this is a first indication of good stability in the extractions then this is a first indication of good stability in the extractions.

Now you can start to extract the measured values of all coffee extractions and list them side by side in a table.
 

The temperature stability can now be calculated in accordance with the definition in the linked document in Excel. For this purpose, the standard deviation is calculated for each extraction and this results in a total standard deviation that is multiplied by 2.

The values will always be slightly different from measurement to measurement and from machine to machine (of the same type). This also applies to the Xenia, even if we calibrate or adjust every machine. The fluctuations are also irrelevant and a machine that has a value below 1.1, for example, will hardly achieve a value above 5 in another measurement.

 

The result of this measuring cycle is: 0.38 and is therefore one of the better results, as you can see in comparison to the other machines listed at https://www.dieroester.at/ kaffeetratsch/ temperaturstabiliaet-bei-espressomaschinen. The document also states that values below 1.1 should be considered good.
 

The measured values are recorded twice: once as a data record (see the link below for the evaluation by Excel) and once as a video so that authenticity can be checked and manipulation can be excluded.

 

Dataset and evaluation:

Measurement with flush

The document describes some optional actions of the measurement cycle, such as the simulation of steaming/ frothing and a flush of the brew group.

As is well known, the Xenia has been developed so that it does not need a cooling flush. At the same time, this means that a flush in Xenia is counterproductive. Nevertheless, you can complete the measuring cycle with a flush provide you stick to the exact timing of flushing for almost exactly 5 seconds: start of the pump until the end of the extraction period = 5 seconds = water flows out of the brew group for 2 seconds.
If you want to complete the measuring cycle with flush with another machine, it is advisable to determine this time in advance — for example with a brew group thermometer.

For comparison to the measurement documented above, this measurement was carried out with flush:

The result of this measuring cycle is again at 0.38 and that primarily means that the flush was well adjusted in the duration for all extractions.
Dataset and evaluation:

Measurement with frothing

If you want to take a measurement with foaming, you first have to determine how long it takes to bring 300ml milk to 60 ° C. With the 2-hole nozzle this takes about 35 seconds.

You have to start frothing immediately at (or shortly before) the start of the extractions and stop foaming about 10 seconds after the extraction is finished since the extractions are shorter in time. This is really tricky at the end, especially with the short intervals.

The result of this measurement cycle is 0.94 and shows that the foaming during the extraction definitely has an influence on the deviations in temperature—even if the value is still good. Whether you can taste it is another question, especially since the milk in the cappuccino makes the espresso less tastable.
Dataset and evaluation:

 

Da die Abläufe wenig Zeit lassen, ist es schwierig den Messzyklus komplett ohne Fehlerzu absolvieren. Auf der anderen Seite ist der Ablauf in der Praxis ja auch nicht immer gleiche.

In the following recording, it was forgotten to start the drawing with activated heating for the first extraction. And the 11th extraction went completely wrong because the boiler was refilled shortly before. The intensive steaming of the previous 10 draws causes the water level in the boiler to drop gradually and so cool water was pumped into the boiler shortly before the 11th extraction. The extraction was started late and had to be stopped soon because the next extraction should start according to plan.
You can see in the graphic on the right that the extraction runs cooler because the boiler pressure was still very low due to the cold water. Since the following extractions had to be stopped every 10 seconds, this dent can also been seen in the following extractions.

Da die Abläufe wenig Zeit lassen, ist es schwierig den Messzyklus komplett ohne Fehlerzu absolvieren. Auf der anderen Seite ist der Ablauf in der Praxis ja auch nicht immer gleiche.

In the following recording, it was forgotten to start the drawing with activated heating for the first extraction. And the 11th extraction went completely wrong because the boiler was refilled shortly before. The intensive steaming of the previous 10 draws causes the water level in the boiler to drop gradually and so cool water was pumped into the boiler shortly before the 11th extraction. The extraction was started late and had to be stopped soon because the next extraction should start according to plan.
You can see in the graphic on the right that the extraction runs cooler because the boiler pressure was still very low due to the cold water. Since the following extractions had to be stopped every 10 seconds, this dent can also been seen in the following extractions.

Since the following references had to be started every 10 seconds, this dent continued with the following extractions, but also adjusted from extraction to extraction to the average of the previous extractions.
Overall, however, the loss was very moderate at 1.1 ° C on the first subsequent extraction. The brew group with the turbulator has effectively prevented a significant drop here.
Dataset and evaluation:

Measurement 11 was excluded because of the error.
The result of this measuring cycle is also 0.94 due to the errors. It is questionable whether this is comparable because 1 extraction is missing or was only carried out very briefly. Surely, you can say: there are similar irregularities and influences in practice and one can safely say that the result of the measurements hardly calls into question the performance of the machine.

Other Machines / Settings

The question is, of course, whether this is the case with every machine and whether other settings (longer extractions, different boiler pressure) change something in the result. The above measurements were all carried out on a series machine.

A different machine was used for the following measurement, which is operated with a extraction duration of 30 seconds (standard) and a higher boiler pressure.

 

Dataset and evaluation:

 

The result of this measuring cycle is 0.45 and thus within the range of the measurements on the white series machine. The longer extraction time and the higher boiler pressure did not lead to any major deviation.
 

 

Criticism and evaluation

 

The measurements with a Scace measuring insert do not, of course, represent 100% reality. There are several indications for this. To name just one: The mass made of plastic may have similar values ​​(heat capacity/ thermal conductivity) to coffee grounds. But it does make a difference whether the water is pushed through the coffee grounds or just bypassed a plastic block. A lot of heat energy is removed from the system when the coffee grounds are knocked out after an extraction—which does not happen when using a Scace measuring insert. was bei der Verwendung eines Scace-Messeinsatz nicht passiert.

 

One can also see critically that such measurements are somewhat idealised. Machines can stand in the draft or in corners where there is no proper air circulation. Nevertheless, it makes sense to create ideal conditions for a measurement in order to achieve comparability. Showing all changing conditions would certainly be interesting, but hardly possible. And the better a machine performs in this measurement/ evaluation under controlled conditions, the more likely it will cope successfully with less than ideal conditions.
In this context, it should also be mentioned that we did not carry out the optional temperature change described (whereas we did carry out measurements with foaming and flushing).

 

How meaningful is such a value? In general: A standard deviation, which is determined by series of measurements, is certainly a much more realistic value than a single degree value read from a Scace gauge at some time and viewed as the 'brewing temperature’. A Scace used in this way is hardly used sensibly.
The calculated standard deviation in connection with the measuring cycle is to be regarded as a kind of overall view or fingerprint of a machine in form of a number (score).

 

Are machines with a high score automatically worse than machines with a low score?
You can't say that across the board and you can safely say that this number is much less important in home use than in world barista championships. And of course this value has no value in an espresso bar in Italy.

 

In the end, it is always decisive how good the espresso tastes and this is primarily due to the roaster and the correct settings of the grinder.

 

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