Espresso is brewed by forcing hot water through finely ground coffee under pressure.

The longer version

Pressure is what separates this brewing method from drip or immersion. Water is heated to just below boiling and pushed through a compact bed of finely ground coffee at roughly nine times atmospheric pressure, completing extraction in well under a minute.

The fine grind exposes a huge surface area, so the short contact time still pulls out plenty of soluble material, including oils that paper filters often hold back. The result is a small, concentrated drink topped with foam formed when carbon dioxide escapes and gets trapped by surface-active compounds. Grind size has to be matched closely to the dose, since small changes alter how fast water passes.

Where this entry sits

Everyday ingredients turn out to be full of quiet chemistry and long history. This collection gathers short, plain explanations of how bread rises, why onions sting, where common spices originate, and how coffee, tea, and chocolate reached the modern kitchen. The full list sits on the Food and Drink page, where every entry is listed in order.