Coffee Brew Ratio Calculator

Brewing is a solid-liquid extraction described by two separate numbers that are often confused. Extraction yield is the mass of coffee solids dissolved divided by the mass of dry grounds, with an accepted target window of 18 to 22 percent. Strength, measured as total dissolved solids in the finished liquid, normally falls between 1.15 and 1.35 percent for filter coffee. The brew ratio controls strength almost directly, while grind size, contact time and water temperature control yield. A 1:16 ratio is about 62 g of coffee per liter of water; the Specialty Coffee Association golden cup figure near 55 g per liter corresponds to roughly 1:18. Espresso is a different regime, using 1:1.5 to 1:3 under about 9 bar in 25 to 30 seconds. Method settings follow from contact time: coarse grounds for full immersion such as a 4 minute French press, medium-fine for a 3 to 4 minute pour over, very fine for espresso. Water at 90 to 96 degrees C, or 195 to 205 degrees F, is standard, since cooler water under-extracts and tastes sour while excessive yield tastes bitter and drying. Several limits apply. Spent grounds retain roughly 2 g of liquid per gram of dry coffee, so cup volume is meaningfully less than the water poured. Volume dosing is unreliable, since a tablespoon ranges from about 5 to 7 g by roast and grind. Water chemistry matters too, with the SCA suggesting around 150 mg per liter of dissolved solids; very hard and fully distilled water both brew poorly.

The numbers behind modern brewing advice come from American industry research in the 1950s rather than from cafe tradition. Ernest Earl Lockhart, a chemist at the Massachusetts Institute of Technology, directed the Coffee Brewing Institute, funded by the coffee trade at a time when US per-capita consumption was falling and weak restaurant coffee was widely blamed. Lockhart's consumer sensory panels mapped which combinations of strength and extraction people preferred, producing the window of roughly 1.15 to 1.35 percent dissolved solids at 18 to 22 percent extraction. That result was published as the Coffee Brewing Control Chart, which plots strength against extraction yield with brew ratios running as diagonal lines across the field. The chart outlived its sponsor. It passed through the Coffee Brewing Center and was later adopted by the Specialty Coffee Association of America, founded in 1982, which repackaged Lockhart's window as the Golden Cup standard used for certifying brewers and training baristas; the SCAA merged with its European counterpart in 2017 to form the present Specialty Coffee Association. Cheap instrumentation then changed home brewing: digital scales accurate to 0.1 g made weight-based dosing practical, and handheld refractometers calibrated for coffee brought dissolved-solids measurement out of the laboratory during the 2000s. The devices themselves have separate lineages: Melitta Bentz patented her paper filter in Germany in 1908, Attilio Calimani filed an Italian patent for a plunger pot in 1929, and Alan Adler introduced the AeroPress in 2005.