WE HAVE LONG BEEN ABLE TO PRODUCE QUALITY DRINKS USING ONLY OUR SENSE OF TASTE TO GUIDE US.
Over the years our understanding of the calibration process has grown immensely largely due to industry tools like the refractometer. Through the data these tools provide, we aim to demystify the extraction process for those that work with our coffee on a regular basis.
Two years ago we created the first iteration of our EXTRACTION WHEEL which helped with troubleshooting the calibration of espresso on the way to an optimal taste balance. During calibration, understanding how variables impact one another and how they change your perception of flavours is the key to producing better tasting coffees.
The Wheel proved quite valuable, with a second version including rate of flow as an indication of which variable to change. We decided to synthesize our approach to calibration and create a new infographic called HOW EXTRACTION WORKS, which is a companion tool to The Wheel. Together they help decode the interrelationships between wet dose, dry dose, grind size, duration, strength, and extraction yield percentage.
We set out to confirm our understanding of these interrelationships and took a systematic approach for isolating the impact of each. We conducted a simple experiment, changing one variable at a time keeping the others constant and measuring the resulting strength and extraction yield.
– OUR HYPOTHESES –
Our experiment was aimed at examining the following hypotheses;
A. As wet dose increases, strength decreases, extraction yield increases
B. As dry dose increases, strength increases, extraction yield decreases
C. As grind size gets smaller, strength increases, extraction increases
We accurately forecasted the influence of wet dose and grind size but it was dry dose as it relates to extraction yield that proved more complicated and is what we’ll focus on here.
– DRY DOSE EXPERIMENT –
Our grind size and wet dose remained constant as we changed our starting dry dose in 0.5 gram increments. The correlation between dry dose and duration was quite linear with an approximate 1 second change for each 0.5 grams of ground coffee you choose to either add or subtract. Each espresso was then rested for 1 minute before we began our sampling procedure to record strength and extraction yield data.
We found that as we increased the dry dose we saw the expected rise in t.d.s, or strength, of our espresso, but were surprised to observe a relatively stable extraction yield across the 7 samples. The samples with dry doses above 18 grams displayed sensory attributes formerly identified as “under extracted”. The data showed they were in fact appropriately extracted. We concluded that it was the concentration of the coffee material within the beverage that was leading us to label them improperly.
More than anything, the disconnect between what we were tasting and how we were describing our experience has led to a change in our language. Knowing that these “properly” extracted coffees had unpleasant taste attributes highlighted the influence of a coffee’s concentration on the sensory experience.
The taste based calibration decisions we have been making moved us in the right direction, but the logic we used along the way is not supported by the results of the above experiment. We took this a step further with a HELPFUL TIP allowing us to assess the taste of each sample’s extraction yield, at the same strength. All of the lower dry doses were quite enjoyable to taste so for each coffee we diluted the strength with filtered water to match the strength of the 16.5g espresso, at 8.7% t.d.s. Using the 4-step method below:
STEP 1. Wet dose / TDS = X
STEP 2. Desired TDS / 100 = Y
STEP 3. X / Y = New beverage weight
STEP 4. New beverage weight - wet dose = AMOUNT TO DILUTE
All espressos leading up to and including the 18 gram starting dose were favourable and deemed adequate to be served in a specialty cafe. It was when we diluted the last 3 shots with dry doses above 18 grams, and when extraction yield began to decline from the peak of 20.55% that we started to observe more abrasive taste attributes often associated with ristrettos or coffees of a higher roast degree.
– EXTRACTION: THE REMIX –
This has led us to reevaluate the language we use in the wheel and supporting infographics. Whereas we had previously described flavours as largely a result of extraction yield, we now put equal importance on strength as it is highly influential on our perceptions of taste. Click below to view each infographic in full…
We are constantly striving to have both sensory and statistical data working in harmony. When both strength and extraction yield reach an optimal balance, it is then that the inherent qualities of a coffee are best represented. This furthers our understanding of the influence of strength when calibrating, and what qualities we can attribute to over or under extraction.