Episode Details

Every coffee maker runs on gravity or pressure. An automatic drip machine lifts water with a thermosiphon: an aluminum tube around a heating element boils the water, and steam bubbles push it up past a one way valve before gravity carries it through the grounds. An espresso machine forces water through fine grounds at about nine bars in 25 to 30 seconds, pulling out sweet oils and acids before slow dissolving tannins arrive. Before paper filters, much coffee was boiled with loose grounds. In 1908 in Dresden, Melitta Bentz punched holes in a brass pot with a nail, lined it with notebook paper from her son, and founded the Melitta brand that same year.

On August 27, 1930, Inez H. Pierce of Chicago filed a patent for an electric vacuum coffee maker, replacing the alcohol burners people used on kitchen tables. Paper filters trap the oils cafestol and kahweol, while the metal mesh of a French press lets them through, which gives a heavier cup and is linked to raised LDL cholesterol. The story ends on the International Space Station, where the ISSpresso uses pumps and steel pipes to push water through coffee in microgravity.

• A vacuum brewer uses steam pressure to push water up, then a vacuum from condensing steam to pull coffee back down.
• French press grounds keep extracting after plunging; a 0.5 liter press is considered spoiled after about 20 minutes.
• Carlsbad and Bayreuth style brewers used double slotted filters of glazed porcelain for a neutral taste.
• Single serve pods pack a filter into the capsule and combine heating with a small pressure chamber.
• In space, surface tension makes water cling to pipes, so the system must shear it loose and deliver coffee into a pouch.