Brewers · 5 min

Espresso Basics: Dose, Grind and Ratio

Espresso variables are tightly coupled: change one and the others move with it. Grind finer and the time lengthens; a longer time changes the yield; a different yield changes the strength. Understanding that chain is where dialling in begins.

What nine bar changes

Espresso forces hot water through the coffee bed at roughly nine times atmospheric pressure. That pressure is the decisive difference from filter brewing.

High pressure extracts a great deal in a short time, which is how twenty-five to thirty seconds produces something so much more concentrated. Pressure also emulsifies the coffee oils into the water, which is where crema and the characteristic texture come from.

The flip side is that mistakes are amplified. Everything is decided in half a minute, so a small grind error changes the result dramatically. A single click that is a nuance in filter brewing is the difference between good and undrinkable here.

Three numbers

A shot is recorded with three figures: dose in grams, yield in grams, and time in seconds. "18 in, 36 out, 27 seconds" is the standard shorthand.

The ratio of dose to yield is the brew ratio. The example above is 1:2, and this ratio is the single largest determinant of a shot character.

Measure by weight, not volume. Crema makes the visible volume a poor guide. Dialling in espresso without a scale is essentially guesswork.

The same coffee at a different ratio is a genuinely different drink. Set the direction here first.
Name	Ratio	Character	Suits
Ristretto	1:1 – 1:1.5	Dense, sweetness-led, little acidity	Dark roasts, milk drinks
Standard	1:2	Balanced	The usual starting point
Lungo	1:3 and beyond	Lighter, acidity forward	Light roasts

A starting recipe

When you open a new bag, start here and adjust until the time lands in range.

Grind size comes first. If the time is outside twenty-five to thirty seconds, fix it with the grinder. Once time is right and the flavor still needs work, move the ratio or the dose: one at a time, as always.

Item	Value	Note
Dose	18g	Match your basket size
Yield	36g	Ratio 1:2
Time	25–30 seconds	From the start of extraction
Temperature	92–94°C	Lower for dark roasts
Pressure	9 bar	Fixed on most machines

Using time to dial in the grind

Time is a diagnostic rather than a goal. At a fixed dose and yield, a short shot means water met too little resistance and a long one means too much.

Situation	Meaning	Adjustment
Under 20 seconds	Too coarse, not enough resistance	One step finer
Over 35 seconds	Too fine, too much resistance	One step coarser
Time right but sour	Under-extracted: temperature or freshness	Raise temperature 1–2°C
Time right but bitter	Over-extracted: ratio too open	Cut the yield to 32g
Time varies wildly	Uneven distribution or tamp	Level, then tamp flat

Channeling, the main enemy

Channeling is nine bar of water finding a weak spot instead of moving through the whole puck. The path is over-extracted while everything else is under-extracted, and both end up in the same cup: sour and bitter at once.

It happens in filter brewing too, but pressure makes it both easier to trigger and more damaging. Any density variation in the bed and the water will find it.

The spent puck tells you. Holes in the surface, or one side collapsed and soggy, means water concentrated there. Evenly damp and firm means it went well.

Beans and records

Espresso wants a longer rest after roasting than filter does. Too much gas makes extraction unstable under pressure, so seven to fourteen days past roast is usually the stable window. If a very fresh bag refuses to dial in, leave it a few days and try again.

Every new coffee needs dialling in from scratch, because roast level, density and freshness all differ. Having records from previous coffees narrows the starting range considerably.

What to record is simple: the coffee and its roast date, the grinder setting, dose, yield, time and taste. Once those accumulate you can find a similar coffee in your history and start near its settings. Few methods repay record-keeping as directly as espresso.