I saw this all over...
Instagram this week. Both coffee consultant Scott Rao, and notable coffee scientists Socratic Coffee brought this interesting process to light. It definitely seems counterintuitive to that adding an Aeropress filter or two to your portafilter when pulling shots of espresso would increase total dissolved solids (TDS) and in turn increase the extraction percentage. For a little back story, the ideal extraction percentage in specialty coffee is around 18%. Achieving higher percentages in the 20+ range consistently and without over extraction is the holy grail of espresso making. Scott stated he had achieved percentages around 25%, so I had to try this myself.
Armed with a freshly cut Aeropress filter, a bag of espresso, and a refractometer (tests TDS), I was ready to roll. I pulled a total of twelve shots. The first three were my control group, I used no filters and just ran standard shots of espresso. The second run of three shots had a rinsed Aeropress filter below the espresso. The third set had a rinsed filter below, and a dry on top. Finally, the last set had a dry one on top.
Through the entire experiment I did notice a significant increase in TDS and extraction percentage. Even though I didn't achieve above 20% I do think with some grind adjustments, and longer shots could make it happen. All of the shots I pulled were 1:2 (18 grams in, 36 grams out), and Scott Rao said he had done 1:3 ratios. Check out the video above to see all the results!