Temperature, pressure, contact time. Every variable shapes what ends up in your cup. Our head roaster breaks down the chemistry of the perfect espresso pull.
Coffee extraction is a chemistry problem. You're dissolving soluble compounds from ground coffee into water. The compounds that dissolve first are the fruity, acidic ones. The ones that dissolve later are the bitter, astringent ones. The art is stopping at the right moment — after enough of the good stuff, before too much of the bad.
At ÆTHER, we pull our espresso at 93°C, 9 bar, with 18g of coffee producing 36g of liquid in 26 seconds. Those numbers aren't arbitrary — they're the result of hundreds of shots mapped against a refractometer.
TDS (total dissolved solids) tells you how much coffee is in the cup. Extraction yield tells you what percentage of the coffee's mass ended up in the liquid. The sweet spot: 19–22% extraction yield, 8–10% TDS for espresso.
But the numbers are the floor, not the ceiling. The real skill is tasting what the numbers mean.