Over a decade ago it was commonly accepted that a single espresso was approximately 30 mL in volume poured in a time between 25 and 30 seconds. This rule for espresso persists to this very day, and whilst not technically wrong, this rule is a very rigid and fixed case that does not have any flexibility for the type of coffee used or how much coffee was dosed in the basket. Enter brew ratios to the rescue.
The brew ratio simply defines the relationship between how much coffee is used (dose) and how much coffee is in your cup (yield).
If it's not already patently obvious, we are going to need a good pair of digital scales accurate to 0.1 gram. This will help us measure our dose and yields. A good pair of digital scales is probably one of the best investments you can make into your coffee setup after your machine and grinder.
The 1:2 ratio is a great starting point for many coffees on the espresso machine. My experience teaching students in our introductory barista course over the last 9 years has been that people tend to prefer espresso brewed at or about this ratio.
A ratio of 1:2 simply means, for every 1 gram of ground coffee, your espresso must weigh twice that. For example, if your dosage is 20 grams in the filter basket for a double espresso, your target espresso yield out would need to weigh 40 grams on scales brewed in a time between 25 to 30 seconds. An 18 gram dose at the same ratio would result in an espresso yield of 36 grams. 22 gram dose in, 44 gram yield out. You get the idea!
A lot of specialty coffee companies will often make recipe recommendations for dose, yield and time where they think their coffee tastes best. These recommended recipes will always be around 1:2 in ratio. Sometimes these recipes call for ratios slightly shorter or slightly longer than a 1:2 brew ratio.
The impact of passing more or less water through your ground coffee will change the final strength of your espresso as well as how much you extracted the grounds. A shorter ratio (less than 1:2) will result in a more intense cup, that has been extracted less. This can have a very pleasing syrupy mouthfeel but have muddled flavours. A longer ratio (more than 1:2) will result in a less intense cup, that has been extracted more. This might achieve better clarity of flavours but often at the expense of body and mouthfeel. It's about finding the right balance between the two that is pleasing for you.
If you’ve ever had any problems dialling in a coffee, grab a pair of digital scales and start weighing!
About the author: David Seng has been teaching barista courses as the Director of Education at The Espresso School since 2009.