Free Shipping on all orders above $40! Shop Now!
#152

Does Grinding Frozen Coffee Beans Impact Brewing & Taste?

A number of baristas in the recent World Barista Championship have been making use of Christopher Hendon's research. He found that coffee beans frozen to -79C and below reacted differently to the grinding process concluding that grinding cold results in a narrower particle size distribution, and reduced mean particle size. But how does that impact the taste in the final cup?
A number of baristas in the recent World Barista Championship have been making use of Christopher Hendon's research. He found that coffee beans frozen to -79C and below reacted differently to the grinding process, concluding that grinding at these temperatures or colder resulted in a narrower particle size distribution and reduced mean particle size. You can read his report on the effect of bean origin and temperature on grinding roasted coffee here. But how does this impact the taste in the final cup? 


We hypothesized that a more narrow and consistent grind size distribution should result in more even and thus higher extractions. Whilst we were carrying out the experiment, we also made a few observations. The temperature of the ground coffee was still very cold after grinding. Since we know that the temperature of the grinds has an impact on the extraction, we decided to add in two additional tests. 1. Allowing the frozen coffee to return back to room temperature (24C) after grinding, then pulling the espresso. 2. Putting the frozen coffee through a very coarse grind first before grinding finer at the calibrated settings, then allowing it to return to room temperature before pulling the espresso.

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 the discussed 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, Kochere 141
Process: Fully Washed
Variety: Ethiopia Heirloom
Roast Age: 10 days from roast date 
Agtron: 53 (Whole Bean), 67(Ground)

Equipment

Grinder: Mahlkönig EK43, Coffee Burrs
Distribution Technique: Stockfleth Method
Tamper: PergTamp 58.5mm diameter
Portafilter Basket: VST 18g
Espresso Machine: Slayer V3
Brew Pressure: Full Brew Pressure at 8 Bars / Measured using Scace II
Brew Temperature: (Controlled Variable / Initial calibration at 95°C(Boiler))
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: 18g Dose, 41g Yield, Shot : 10s Pre-infusion, 18s 8 bar full pressure, Total brew time: 28s
                   Water temperature : 93.3°C(Grouphead). Final EY 22.32%.
Dose Tolerance: 20g ± 0.1g
Shot Tolerance: 40.0g ±  0.5g

Hypothesis 1:

Frozen coffee ground at -79°C will enable more even and higher espresso extractions.

Methodology :

(Steps)
1. Prepare pre-weighed coffee doses, frozen to -79°C in dry ice for at least 3 hours.
2. Calibrate the coffee to be overextracted, slight bitterness in the finish.
2. Pull 5 espresso shots using the calibrated settings.
3. Pull 5 espresso shots using frozen coffee, ground and brewed immediately.
3. Pull 5 espresso shots using frozen coffee, ground and allowed to return to room temperature after 20 minutes before brewing.
3. Pull 5 espresso shots using frozen coffee, ground and allowed to return to room temperature after 20 minutes before brewing.
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:


ControlFrozen->Espresso

Frozen->Room Temp

->Espresso

Frozen->Double Grind->

Room Temp-> Espresso

YieldTDSEYYieldTDSEYYieldTDSEYYieldTDSEY
141.209.41%22.32%40.809.46%22.22%41.109.36%22.15%41.409.03%21.52%
241.209.32%22.11%41.209.62%22.82%41.009.77%23.06%41.409.17%21.86%
341.209.55%22.65%41.009.53%22.49%41.409.31%22.19%41.309.33%22.18%
441.009.54%22.52%41.109.53%22.55%41.309.45%22.47%41.309.38%22.30%
541.409.23%22.00%40.909.41%22.16%41.309.65%22.94%41.609.22%22.08%
Average EY%22.32%22.45%22.56%21.99%
EY% Range0.65%0.66%0.91%0.78%
Standard Deviation0.0027175360.0026715160.0042055920.003074411
Variance7.39E-067.14E-061.77E-059.45E-06
P-Value10.4741266980.3164314070.108582699
10.6251568760.036045839
10.04174497
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 with the frozen coffee. However, upon closer inspection, all the calculated P-Values are greater than 0.05. This means that we do not have statistically significant results to support our hypothesis. Using frozen coffee ground at -79°C does not result in higher coffee extraction percentages.

Although the results that we have obtained do not show any statistical significance, there is a noticable difference in terms of taste across the different espressos pulled using the frozen coffee. So although there is no statistical significance mathematically, the small differences in extraction might show significant difference in taste. Another explanation could also be the possible 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.

Here are the tasting notes recorded for each of the espresso shots:

Control: Floral & sweet, slight bitterness in the finish.

Frozen -> Espresso: Floral & sweet, reduced bitterness in the finish but still traces present.

Frozen -> Room Temperature -> Espresso: Floral & sweet, no bitterness detected.

Frozen -> Double Grind -> Room Temp. ->Espresso: Floral & sweet, slight sourness in the start. No Bitterness

Even though the experiment results do not show any significant evidence to support the hypothesis, there was noticeable differences in taste. Coffees brewed using the frozen coffee had significantly reduced bitterness. Surprisingly, the frozen coffee that went through the double grind process tasted slightly underextracted plus there is also a statistical difference when compared to the extractions of the other frozen coffees. The extractions were significantly lower and tasted as such. It might be possible that coffee that has gone through this process has a significantly different grind size distribution and would require a different calibration as opposed to the control. There is no evidence to support if it will be able to provide a higher or lower extraction.

Since there are significant differences in taste, future studies may look into the chemical makeup of espressos pulled using the different frozen coffees 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 espresso and is not the be all and end all. We should always still taste the espresso and allow our taste buds 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 experiments that we are conducting, do subscribe and support us by buying some awesome coffee here!