The main goal of brewing espresso is to extract the ground coffee at the right level of extraction (ie. well-extracted) - not over-extracted, and not under-extracted. Over-extracted brewing will make it overly bitter, under-extracted will make it overly sour. Both are not pleasant to drink.

Brewing espresso has a few factors (variables), and their implications to the extraction.

Variables Implications
Ground level Finer ground will extract more, coarser ground will extract less
Water temperature Hotter temperature will extract more, colder temperature will extract less
Brewing time Longer brewing time will extract more, shorter brewing time will extract less
Brewing ratio More ground coffee will extract more, less ground coffee will extract less

What we can do to simplify the espresso brewing is to isolate two variables, and leave us with just one variable to change. The following is the rule of thumb (ie. recipe) for well-extracted espresso.

  • Brewing ratio is 1:2 to 1:2.2 (eg. 18 grams of ground coffee, output 36 to 39.6 grams of espresso )
  • Water temperature is 93C
  • Brewing time is between 25s to 35s
  • Ground level is the one that you need to tweak