By PETER GIULIANO
In 1957, Professor E. E. Lockhart, Scientific Director of an organization called the Coffee Brewing Institute, wrote:
“…the most acceptable cup of coffee would be prepared if the soluble solids ranged between 1.15 and 1.35 percent and the extraction between 18 and 22 percent.”
— From the Soluble Solids in Beverage Coffee as an Index to Cup Quality
This opinion was based upon the work of a number of brewing committees and research institutes, and represented the best thinking about coffee extraction at that time. Since then, these guidelines (particularly the window of 18-22 percent extraction as being ‘optimal’ for brewed coffee) have become the basis for innumerable brewing standards, guidelines, instructions, and formulas all over the world. But could this be a truly universal thing? Could it be that ‘the most acceptable cup of coffee’ might vary according to geographic or cultural preferences?
In 2010, a group of researchers from the heritage Speciality Coffee Association of Europe (SCAE, now the Specialty Coffee Association) asked exactly this question, and put their minds together to design a consumer study to test the assumptions implicit in the the 18-22% extraction window.
What is this extraction window, exactly? Well, think of it this way: roasted coffee is a little bit like a sponge. The sponge itself cannot be dissolved in water, but the sponge is loaded with flavorful material that will dissolve. This is why grinding coffee and pouring hot water over it creates the flavorful beverage we call ‘brewed’ or ‘filter’ coffee. A little more than 30 percent of this ‘sponge’- the coffee bean- is soluble by pouring hot water over it.
Except there is a rub: due to differences among these extractable substances, if you extract all 30+ percent, the coffee doesn’t taste very good: bitter and ‘overextracted’ flavors interfere with enjoyment of the coffee. So where to stop an extraction? Lockhart and others proposed 18-22% as the ideal window- enough extraction for it to taste delicious, not so much as to cause it to be bitterly overextracted.
However, since there is a subjective element to taste which can vary from consumer to consumer and from culture to culture, it’s reasonable to expect that there will be some people who prefer coffee outside that ‘ideal’ window. Who could they be, and might they vary according to their geography?
The SCAE research group devised an ambitious study to perform consumer preference studies in four cities across Western Europe- Dublin, Ireland; Maastricht, the Netherlands; Cologne, Germany; and Milan, Italy- to find out whether consumers in those cities would prefer coffee within that 18-22% range. The experimental design included precisely brewing coffee to 5 different extraction percentages keeping the brew strength exactly the same. In all, 641 consumers tasted these coffees, and scored them on a continuum between “Like Extremely” to “Dislike Extremely”. The details of the experiment are shared in the final report (available to SCA members here).
The results, published as “European Extraction Preferences in Brewed Coffee” in 2013, are fascinating. Indeed, preferences seemed to vary from city to city. And, though the overall results seemed to support the industry-standard 18-22% window, there were also some surprises, including some evidence to support the ‘Double Hump’ hypothesis of Scott Rao and James Hoffmann, among others.
It’s really engrossing reading, particularly for those coffee people fascinated by the nuances of coffee extraction. Like all great research, it raises new questions even as it illuminates: how might extraction preferences vary in geographies elsewhere in the world? How does coffee strength play in to the equation?
This is really good research, obviously performed by passionate and talented coffee professionals. It’s exactly the kind of thing that our coffee community can do— come together, identify, challenge, and illuminate some of the fundamentals of coffee extraction and preparation.
The full report— and many others— is available for free to all SCA members on our Members Research Portal. Do you need the password to access the portal? Email our Member Services team at membership[at]sca.coffee.
Not yet a member? Join us to support the mission of the SCA, a nonprofit trade association, and receive complimentary access to this report and many more. Visit sca.coffee/join to join today.