Physics World feature synthesizes three espresso studies: pressure limits cap at 9 bars, channelling kills extraction, coarser grinds improve shot reproducibility.
Key Takeaways
Arabica prices surged 80% in 2024 from climate disruption; UK supermarket beans up 20%, instant coffee up 40%, coffee shops up 30% since 2021.
Poroelastic effect: espresso puck compresses as pressure rises, collapsing pores. Darcy’s law holds only below 5 bars; flow rate peaks at 8-9 bars regardless of higher pressure.
Most dissolved solids extract within 30-35 seconds; the peak sweet spot is 15-20 seconds where increasing flow rate and decreasing solids concentration briefly align.
Channelling (water finding least-resistance paths through the puck) sharply cuts total dissolved solids; uneven tamping and poor distribution are the primary causes.
Hendon’s Coffee Science Foundation study found less coffee ground more coarsely yields more reproducible shots, countering the intuition that finer grind maximizes surface area and extraction.
Hacker News Comment Review
One commenter flags a practical tension: if coarser grind and less coffee both speed up flow, hitting the conventional 20-30 second target window requires recalibration the studies do not spell out.
