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Experiment #157 : Grinder Temperature and Extraction

For awhile now, we've experienced a streak of inconsistent timings with our espresso brewing. Shot timings changed significantly across the day which had our whole team scratching their heads. After reading about The resistance of Heat by Michael Cameron, it seems like his discovery about the grinder's temperature rising and decreasing across the day has a significant impact on the resulting extraction and shot times. We've set out to investigate this mystery with a couple tweaks of our own.

We decided on the test using the same grinder as Michael, the Mythos One Climapro Grinder but this time in two different states. The first will involve the heating elements unplugged with no interference to the grinder burr temperatures. The second state will involve having the built-in heating element plugged in. This means that there will be a heated chamber where beans will reside prior to being ground. The fan elements will also be activated and kick in at certain intervals to regulate the overall temperature of the burrs and the heated chamber.

Disclaimer : We are by no means statistical / math / science experts. This is just a simple experiment carried out to give us an idea of the performance of each method only. People are more than welcome to give their feedback on how we can improve and carry out a more academically approved experiment / report.

Null Hypothesis

Higher grinder burr temperatures decrease espresso shot times and extraction


Uganda Sipi Falls, Organic Certified
Process : Fully Washed
Variety: SL14 & SL28
Roast Age: 32 days from roast date 
Agtron : 58 (Whole Bean), 70(Ground)


Grinder : Nuova Simonelli Mythos One Climapro Grinder
Distribution Technique : Stockfleth Method
Tamper : PergTamp 58.5mm diameter
Portafilter Basket : VST 18g
Espresso Machine : Slayer V3
Brew Pressure : Full Brew Pressure at 7 Bars / Measured using Scace II
Brew Temperature : (Controlled Variable / Initial calibration at 93.3C)
Grouphead Flow Rate : 117g water / 10s ( Full Brew Pressure ), 28g water / 10s (Pre-infusion Brew Pressure set to maximum 3 bar)
Coffee Refractometer : VST Coffee III
Calibration : 
(Heating Element Plugged In) 18g:40g, Pre-brew: 14", Total Time: 37", TDS: 9.32% Ext%: 21.46%, Chamber Temp: 37.3, Grind Temp: 39.3
(Heating Element Unplugged) 18g:39.6g, Pre-brew:11", Total Time: 30", TDS:9.31%, Ext. 21.22%, Chamber Temp: 49, Grind Temp: 45.6
*Optimal Calibration is set at the furthest possible point in extraction whereby minimal to zero astringency or notes of over-extraction is detected in the cup.
Dose Tolerance : 18g
Shot Tolerance : 42.0g ±  0.5g

Methodology :

1. Hook up thermoprobes to the bean chamber and the grinds exit chute.
-   See Picture Below

2. Calibrate coffee with the heating element unplugged.
3. Pull 20 espressos in succession using the calibrated settings and measuring shot timings.
4. Allow espressos to cool before measuring Total Dissolved Solids (TDS%) and Extraction percentages.
5. Calibrate coffee with the heating element plugged in.
6. Pull 20 espressos in succession using the calibrated settings and measuring shot timings.
7. Allow espressos to cool before measuring Total Dissolved Solids (TDS%) and Extraction percentages.


Calibration: 18g:40g, Pre-brew: 11", Total Time: 33", TDS: 9.32% Ext%: 21.46%, Chamber Temp: 37.3, Grind Temp: 39.3Calibration: 18g:39.6g, Pre-brew:11", Total Time: 30", TDS:9.31%, Ext. 21.22%, Chamber Temp: 49, Grind Temp: 45.6
Without Heating ElementWith Heating Element
No.DoseYieldTDS %Ext. %Pre-brew TimeTotal Ext. TimeBean Chamber TempPeak Grind Output TempNo.DoseYieldTDS %Ext. %Pre-brew TimeTotal Ext. TimeBean Chamber TempPeak Grind Output Temp

Conclusion :

After measuring the results, there doesn't seem to be any significant correlation between the extractions obtained throughout the 40 shots and the temperatures of the grinds. With the heating element plugged in, the flow was similar but it could not reach the same level of extraction without obvious bitterness showing. We needed a slightly coarser grind size in order to obtain optimal extraction. The one observation we made is the bigger variance in extraction percentages when the heating element was plugged in.

In the end, there was no conclusive evidence to show that higher grind temperatures resulted in quicker shot times or lesser extractions. This is contrary to a few literature where the belief is that a higher grind temp would affect the rate of extraction. However, it definitely did result in a differing taste. This could be caused by multiple variables such as a different grind particle distribution due to higher temperatures, and differing compounds being dissolved as a result either of the temperature or the different grind particle distribution. It is worth noting that even though the extraction % gives us an indication of how much coffee was extracted, it does not tell us exactly WHAT was extracted and the chemical makeup of the compounds in the resulting espresso could be very different from that of the lower temperatures; giving us a different taste experience. If only we could identify all the compounds dissolved into the coffee from each extraction. Hmmm... time for some new equipment maybe?

A key variable that is different from our daily routines is also the amount of rest the coffee has gotten. The coffee used for this experiment was rested for a month whereas our usual coffee lies in between 7 - 15 days. The amount of degassing could potentially affect the results. Another potential idea for our next experiment!

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