Free Shipping within Singapore on all orders above $60!

Hot or Cold? The Best Temperature for Brewing Espresso

For the past few decades, temperature stability has been a major goal for many espresso machine manufacturers and also one of the deciding factors of the quality of an espresso machine. There is without a doubt, a huge emphasis placed on temperature in the brewing process of espresso. So how exactly does temperature affect espresso and the brewing process? What is the final impact on the extraction of the coffee when brewed using different temperatures? This week, we set out to explore exactly how espresso extraction is affected by different temperatures.

As water acts as the dissolving agent for coffee, there is a common consensus that a higher temperature would improve it's efficiency as a dissolving agent because of its increased thermal energy. This would mean that with higher temperatures, there should theoretically be higher extractions due to the improved dissolving abilities of the water. For this week's experiment, we will set the null hypothesis as "Higher temperature water does not result in significantly higher extraction percentages in coffee" and seek to find evidence to reject the null hypothesis.

If you are unfamiliar with the workings of expresso extraction percentages and the use of the coffee refractometer, you can always read our previous article over here to get a quick overview and understanding of espresso extraction percentages.

Now let's dive straight into the experiment!

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.

Coffee 

Ethiopia, Sidamo Guji 
Process : Natural Sundried
Variety: Heirloom
Roast Age: 12 days from roast date 
Agtron : 63.5 (Whole Bean), 82(Ground)

Equipment

Grinder : Nuova Simonelli Mythos One Climapro Grinder
Distribution Technique : Stockfleth Method
Tamper : PergTamp 58.5mm diameter
Portafilter Basket : VST 20g
Espresso Machine : Slayer V3
Brew Pressure : Full Brew Pressure at 7 Bars / Measured using Scace II
Brew Temperature : (Controlled Variable / Initial calibration at 91C)
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 : 20g Dose, 40g Yield, Shot : 10s Pre-infusion, 19s 7 bar full pressure, Total brew time: 29s
                   Water temperature : 91.3°C. Final EY 19.1%.
*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 : 20g ± 0.1g
Shot Tolerance : 40.0g ±  0.5g

Null Hypothesis 1:

Higher temperature water does not result in significantly higher extraction percentages in coffee

Methodology :

(Steps)
1. Calibrate the coffee using 91C water temperature.
2. Pull 10 espresso shots using the calibrated settings.
3. Pull 10 espresso shots using 92C water temperature.
3. Pull 10 espresso shots using 93C water temperature.
3. Pull 10 espresso shots using 94C water temperature.
3. Pull 10 espresso shots using 95C water temperature.
11. Wait for espresso shots to cool to room temperature.
12. Measure Total Dissolved Solids (TDS%) and Extraction % for each sample.

Results:


91C92C93C94C95C
Yield TDS EY Yield TDS EY Yield TDS EY Yield TDS EY Yield TDS EY
1 40.00 9.89% 20.50% 39.80 9.46% 19.51% 40.10 9.16% 19.03% 40.40 9.23% 19.32% 40.00 9.67% 20.04%
2 40.00 8.68% 17.99% 40.20 9.16% 19.08% 39.90 9.68% 20.01% 40.00 9.97% 20.66% 40.40 9.49% 19.87%
3 39.60 9.11% 18.69% 39.50 8.92% 18.26% 40.00 9.26% 19.19% 40.10 9.87% 20.51% 39.90 9.27% 19.16%
4 40.20 8.85% 18.43% 39.80 9.79% 20.19% 40.10 9.25% 19.22% 40.30 9.08% 18.96% 40.50 9.08% 19.05%
5 40.00 8.53% 17.68% 39.90 8.83% 18.25% 39.50 8.95% 18.32% 40.00 8.80% 18.24% 40.00 9.45% 19.59%
6 39.70 9.51% 19.56% 40.20 8.66% 18.04% 40.10 8.94% 18.57% 40.00 9.12% 18.90% 40.00 9.28% 19.23%
7 39.80 8.93% 18.42% 39.70 8.93% 18.37% 40.00 9.31% 19.30% 40.10 8.90% 18.49% 40.30 9.37% 19.57%
8 39.90 9.47% 19.58% 40.30 9.91% 20.69% 40.00 8.94% 18.53% 40.10 9.07% 18.84% 40.30 9.41% 19.65%
9 40.00 8.69% 18.01% 40.00 9.06% 18.78% 40.10 9.63% 20.01% 40.00 9.08% 18.82% 40.00 9.19% 19.05%
10 39.60 9.49% 19.47% 40.00 9.69% 20.08% 39.90 9.02% 18.65% 40.40 9.14% 19.13% 39.80 9.15% 18.87%
Average EY% 18.83% 19.13% 19.08% 19.19% 19.41%
EY% Range 2.82% 2.65% 1.69% 2.42% 1.17%
Standard Deviation 0.009032048 0.00944331 0.005904245 0.007967022 0.003901225
Variance 8.15779E-05 8.91761E-05 3.48601E-05 6.34734E-05 1.52196E-05
P-Value 1 0.48885601 0.474707487 0.365125068 0.088866911
1 0.906645418 0.875731273 0.39830938
1 0.744303776 0.166237351
1 0.44484636
1


Conclusion:

For those who might be unfamiliar with statistics, you can read the conclusion of our previous article to get a quick explanation on statistical significance here.

Looking at the results that we have obtained, there seems to be a trend of increasing extraction percentages as we use higher brew temperatures. However, upon closer inspection, all the calculated P-Values are greater than 0.05. This means that we do not have significant results to refute the null hypothesis. Higher brew temperatures do not result in higher coffee extraction percentages.

Although the results that we have obained do not show any statistical significance, there is undoubtedly a difference in terms of taste across the different espressos pulled using increasing brew temperatures. So although there is no statistical significance methematically, the small differences in extraction might prove to create significant difference in taste. Another explanation would also possibly be the chemistry makeup of the resulting espresso. Although the numerical percentage of total dissolved solids might be similar, the chemical makeup of those dissolved solids could potentially be significantly different, giving rise to the difference in taste.

In conclusion, the experiment results do not show any significant evidence to refute the null hypothesis. There is no evidence to support that higher brew temperatures result in higher extraction percentages. However, since there is significant differences in taste, future studies may look into the chemical makeup of espressos pulled using different temperatures to discern the reasoning behind the changes in taste. It is also worthy to note that this is a great example to show that numerical measurements such as TDS and Extraction percentages only serve as guide and reference in our understanding of epresso and is not the be all and end all. We should always still taste the espresso and allow our tastebuds to guide us at the end of the day since our customers do not judge our coffees through measurement devices but rather their own sense of taste and smell as well.

Last but not least, if you like the content that we are giving out don't forget to subscribe and support us by buying some awesome coffee here!

2 Comments

    • Avatar
      Darule
      Jan 20, 2017

      I think this experiment needed a wider temperature range to make it more meaningful. You could have used a lower temperature to begin with of 65C and increased at a constant interval up to 95C. Extraction equipment is a limiting factor here but it doesnt have to be espresso extraction. I bet the results will show an increasing TDS that plateaus at a certain temperature. Given that cold brew still extracts solids over a period of time, cooler temperatures are relevant to this experiment. Also you comment on a difference in taste between the temperatures, can you describe what the taste characteristics are for each temperature?

      • Avatar
        Kenneth
        Jun 6, 2017

        Hi Darule, I think majority of coffee shops wouldn't be brewing their espressos at 65C, but its definitely worth some research to use wider temperature ranges. I don't want to comment too much on the taste differences as it might be a bit subjective but generally the higher temperatures presented harsher and more bitter/astringent flavors with a mouth feel that tends to be more rough and dry. It could be attributed to over-extraction from the higher temperatures as the other variables remain the same. Hard to say if the chemical make-up itself is substantially different.

Leave a Reply

* Name:
* E-mail: (Not Published)
   Website: (Site url withhttp://)
* Comment:
Type Code