The short answer
Without a refractometer, use a scale and a timer. La Marzocco starts at 18 g in and 36 g out (1:2) and aims for a 25-35 second shot; Breville's dial-in guide aims for 25-30 seconds. Hold dose and ratio fixed and change only grind: finer if the shot runs fast and sour, coarser if it runs slow and bitter.
Why ratio comes before grind
Brew ratio is the weight of the coffee grounds against the weight of liquid espresso in the cup, and a scale measures both sides of it. La Marzocco's article on brew ratios defines it that way and calls it easy to measure with a scale. Breville's dial-in guide adds that weighing gives "a more accurate picture" of dose and yield than measuring by volume. An espresso scale can read to a tenth of a gram: Acaia's spec sheet lists 0.1 g readability for its Lunar.
Once dose and yield are fixed, grind is the variable left to set the flow. With dose and yield locked in, grind size "will determine how water flows through the coffee", in the words of La Marzocco's Coffee Station guide. Breville's dial-in guide gives the general rule: change one variable at a time and keep everything else the same. Two variables moving at once produce a result that cannot be traced to either of them.
The dial-in loop
Run the same five steps for every shot and change exactly one thing between shots. Each target below names the guide it comes from.
| Step | What you do | Target | Source |
|---|---|---|---|
| 1 | Weigh the dose | 18 g | La Marzocco |
| 2 | Distribute and tamp level | dense, evenly packed grounds | Breville |
| 3 | Start the shot and the timer together | clock starts with the brew | Breville |
| 4 | Stop at the output weight | 36 g | La Marzocco |
| 5 | Read the clock | 25-30 s | Breville |
If step 5 misses, change the grind by a small step and repeat. Breville's guide warns that "even minor adjustments can make a big difference", and offers a gram or two of dose as a second lever. This loop leaves the dose alone so the ratio stays fixed, and moves only the grinder: La Marzocco says to grind finer when the shot flows too quickly and coarser when it flows too slowly.
What each failure tastes like
A shot that runs fast tastes sour and thin: Breville's dial-in guide describes a shot that delivers its yield too quickly as "a sour, thin-bodied cup" and fixes it with a finer grind. A shot that runs slow tastes bitter: the manual for Breville's Dual Boiler (BES920) says a grind that is too fine makes over-extracted espresso, "dark in color and bitter in flavor". The extraction guide in the same manual marks a shot under 20 seconds as under-extracted and one over 40 seconds as over-extracted.
Sour means finer, bitter means coarser: that is the machine makers' rule of thumb, and it has limits. The SCA's summary of UC Davis research says bitterness "is maximized at high TDS and PE", so strength (total dissolved solids, TDS) feeds bitterness along with extraction (percent extraction, PE). The studies behind that summary are the ones the Coffee Science Foundation lists for the UC Davis project: none of them is about espresso, and the ones that name a brew method used drip or full-immersion brewing.
What the numbers mean
In La Marzocco's naming, brew ratio names cover ranges, not points. La Marzocco's article on brew ratios puts "a 1:1 to a 1:2" as ristretto, "1:2 to a 1:3" as normale and "a 1:3 to a 1:4" as lungo, with "wiggle room for interpretation". It describes a ristretto as "viscous with a heavy body" and says that as the ratio extends, "clarity increases, body and viscosity decrease". Breville's dial-in guide uses single points instead: ristretto at 1:1, lungo at 1:3, and 1:2 as "the golden standard". La Marzocco's Coffee Station guide calls 18 g in and 36 g out a "Normale" recipe.
Extraction yield is "the mass fraction of soluble solids removed from the coffee grounds", in the definition used by Batali, Ristenpart and Guinard (Scientific Reports, 2020). A refractometer does not read it directly. It reads total dissolved solids (TDS), the strength of the drink, and extraction is then calculated as TDS × beverage mass ÷ dose, which is how that paper computed it. The SCA describes the same method: "measuring TDS and calculating PE".
What the clock can and cannot tell you
Without a refractometer, shot time is the cue the machine makers use. Breville's dial-in guide calls 25-30 seconds ideal and says a great-tasting espresso can take anywhere between 20 and 40 seconds. La Marzocco says a finer grind slows the shot down.
Time is a cue, not a measurement. In espresso experiments published in Matter in 2020, Cameron and colleagues found that extraction yield peaked at a middle grind setting, "with lower extraction yields at both very coarse and fine settings", and read the drop at fine settings as uneven flow through the coffee bed. Put that next to the makers' advice that a finer grind slows the shot, and a slower shot is not proof of a more extracted one: past that peak, grinding finer lowered extraction instead of raising it.
Where the guides disagree
The guides behind this post agree on the method and differ on the numbers:
- Shot time. 25-30 seconds in Breville's dial-in guide; 25-35 seconds in La Marzocco's Coffee Station guide and in the extraction guide of the Breville Dual Boiler (BES920) manual.
- Dose. La Marzocco starts at 18 g (Coffee Station guide); Breville calls 18-22 g "a safe start" (dial-in guide).
- Ratio names. La Marzocco's ranges meet at the edges, so 1:2 is both the top of its ristretto range and the bottom of its normale range (brew-ratio article); Breville gives single points instead (dial-in guide).
None of these differences changes the loop: fix dose and yield, then let the clock and the taste steer the grind.
When to stop adjusting
Stop when shots land inside the time window and taste the way you want them to. Breville's dial-in guide ends on the same point: trust your palate, and once a shot tastes right, take notes of the measurements, timing and settings. Write the grinder setting next to the roast date on the bag, a date Breville's freshness guide tells you to watch.
The setting will not hold for the life of the bag, because the coffee keeps changing. The SCA's Coffee Decoded column says whole beans lose CO₂ fastest in the first 20 days after roasting. Breville says that CO₂ "plays a key role in extraction", and La Marzocco says espresso needs fine-tuning for changes in "coffee freshness". None of the three says which way the shot drifts as beans age, so re-check the clock instead of assuming.