Advanced Espresso

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Æ Grinding

Æ 1.07 Recap & Glossary


  • Extraction in espresso occurs only at the surface of particles  — this is called erosion
  • This means a fine grind is required, and the smallest particles are especially important in extraction
  • Grinders exert two kinds of force on coffee: compression and shear
  • Different grinder types apply these forces in different ways
  • The grind size from any grinder isn’t uniform, but a distribution of different sized particles
  • Small particles contribute a disproportionate amount of the surface area for extraction, while larger particles play an important role in allowing sufficient flow through the puck
  • Grind shape also plays a role in extraction that is not yet well understood
  • Grind size distributions are measured in the laboratory using laser diffractometry
  • Baristas can measure grind size distributions directly using the new Barista Hustle app