The Science of Coffee An Analysis of Total Soluble Extract Resultant from Various Coffee Brewing Methods

Abstract and Background Since the 1950s there have been multiple coffee taste-preference trials. The original was performed by the Brewing Committee of the National Coffee Association1 wherein it was determined that the main factors affecting taste-preference are: Total dissolved solids, e.g. the strength of the brew Soluble Extract, e.g. the percent of the beans extracted to derive the brew strength The Total dissolved solids (TDS %) present in a given cup directly correlates with coffee strength—the greater the TDS % the higher the strength of the resultant brew. The Soluble Extract (SE %) represents the portion of the beans that were used to derive the TDS %. The greater the percentage of the ground beans material extracted into a solution (the SE %), the more likely you are to extract bitter compounds from the beans. The smaller the percentage of ground beans that are extracted into a solution, the less likely you are to extract desirable components from the ground beans. I conducted a series of trials comparing three available methods of brewing across the two important factors of taste as determined in previous experiments.

Materials and Methods Each coffee brewed, in order to be comparable, should be brewed to comparable standards. For this project I chose to adhere to the Specialty Coffee Association of America (SCAA) cupping standards2. Brew variables Water 3 Water Preparation: 10L Distilled Water 0.3g CaCl 2 0.2g NaCl 0.3g Ca(OH 2 ) Water Target: Total Hardness as CaCO 3 ~ 61ppm Total Alkalinity as CaCO 3 ~ 41ppm Sodium ~ 8ppm

Water-to-coffee-ratio 4 0.055g coffee per 1 ml water

Water Temperature 203°F—Roughly boiling temperature for Longmont.

Grind All grinds done on the "8" setting of a Baratza Maestro Plus Conical Burr Grinder

Trials Three trials were performed for each brew method to ensure consistency TDS % and SE % Measurement TDS % was tracked via two methods: TDS Meter—As sold on the SCAA website5 Brix % Refractometer The Brix % of a solution is a measure of the sugar content of a solution. Since the sugar content of a coffee extraction varies directly with the TDS % of a solution, a formula can be applied to derive the TDS % from the Brix %: Brix % * 0.85 = TDS % 6 After the TDS % is measured or derived, calculation of the total percentage extraction of bean weight extracted is relatively simple: Total Coffee Brewed(g) * TDS % / Beans Used(g)7 Methods of Brewing After the TDS % is measured or derived, calculation of the total percentage extraction of bean weight extracted is relatively simple: Three methods of coffee brewing were chosen, primarily by choosing brewing products which I already owned. This, however, was not the case for the Mr. Coffee machine which I procured from the local Goodwill store. The three methods of brewing that were tested were: Chemex Coffee Maker Aeropress Mr. Coffee

Results Method Trial Coffee (g) Water (g) Yield (g) Brix % TDS % (derived) TDS % (measured) SE % Mr. Coffee 1 38.5 700 606 1.90 1.62 1.51 25.42 2 565 1.90 1.62 1.42 23.70 3 587 1.90 1.62 1.43 24.25 Chemex 1 38.5 700 622 1.3 1.105 1.09 17.85 2 625 1.4 1.19 1.21 19.31 3 621 1.3 1.11 1.17 16.93 Aeropress 1 11 200 187 1.1 0.94 0.99 15.90 2 187 1.2 1.02 1.13 17.34 3 190 1.1 0.94 1.1 16.15 Comparing Total Dissolved Solids (TDS)% with Soluble Extract%