You open a new bag and the first cup tastes weaker than last week. The reflex is to add another scoop. Before you do, look at your coffee to water ratio: how many grams of coffee you use for how many grams of water. That number tells you what actually changed in the cup, as long as you keep it where it is.
Coffee to water ratio: strength and flavour are two separate dials
The word "strong" usually covers two things.
The first is concentration: how full and heavy the coffee feels in your mouth. The ratio is the main control for that. 15 g of coffee to 250 g of water (about 1:16.7) gives you a regular cup of filter coffee. The same 15 g to 300 g of water gives a lighter cup with a similar character.
The second is extraction: how much the water pulls out of the bean. This is where coffee turns sweet, sour, or bitter and dry. Grind size, contact time and water temperature control it.
Coffee people have worked with these two axes since the 1950s, on the Coffee Brewing Control Chart: strength on the vertical, extraction on the horizontal. In 2023 a team at UC Davis (Guinard, Ristenpart and colleagues) published a new version of the chart in the Journal of Food Science, built on what consumers actually liked. They found two groups of consumers with different tastes in strength and extraction. So the right ratio is yours. Find it once, then leave it alone.
Coffee to water ratio held fixed when the batch changes
We roast in small batches, outdoors, on Saturdays and Sundays. Before every batch, Laurent reads the weather and adjusts the fire and the time on Golden to land on the same flavour target. The target stays put, while the route to it shifts a little from day to day, so the bean can come out slightly denser or slightly more porous. The mechanism is in our piece on differences between batches roasted the same weekend.
At home, that gives you one simple rule. The ratio stays fixed from bag to bag. If the new bag tastes different, you correct the grind. Change dose and grind on the same morning and you lose track of which one did the work.
Holding a ratio steady takes a scale. A scoop measures volume, and that volume weighs differently from one batch to the next. The details are in our article on how many grams are in a scoop of freshly roasted coffee.
The three cup test for your coffee to water ratio
It takes about 20 minutes, and you do it once for each brew method you use.
1. Weigh out 15 g of coffee three times, ground at your usual setting. 2. Brew three cups with the same method and water at 93°C (about 199°F), changing only the water: 225 g (1:15), 255 g (1:17), 285 g (1:19). 3. Let them cool for 5 minutes to the same temperature. Very hot coffee hides a lot. 4. Taste in order, from the most diluted to the most concentrated.
How to read the result:
- If the three cups differ only in how full they feel, the ratio is your lever. Pick the one you like and write the ratio on the bag, next to the roast date.
- If all three share the same flaw (sour up front, or bitter and dry at the finish), the problem is extraction. The ratio only dilutes or concentrates that flaw. You fix it with the grind.
Coffee to water ratio or grind size: what to move when it goes wrong
- Watery, but clean tasting: tighten the ratio by two steps, from 1:17 to 1:15. Leave the grind where it is.
- Too heavy, but sweet: pour 30 g of hot water straight into the cup. Diluting after brewing changes strength only, which makes it the safest test.
- Sour and thin: keep the dose and grind one step finer.
- Bitter, with a dry finish on the tongue: one step coarser. The signs of overextraction are in our article on coffee ground too fine.
- New bag, batch from another day: brew the first cup at your old ratio and old grind setting. From there, adjust only the grind, one step per morning.
Espresso follows the same logic with different numbers: 18 g of ground coffee gives 36 g in the cup (1:2). Hold 1:2 and adjust the grinder until the shot runs in 25 to 30 seconds.
Thursday 1 October is International Coffee Day. Run the three cup test before then and tell us which ratio won in your kitchen. On Saturday or Sunday you'll find us at Marché de l'Abattoir, by the exit of the Manufakture car park, in Anderlecht. Tell Laurent your ratio and your brew method, and he'll give you a starting grind setting for that day's batch. You can also find the coffee at meteokoffie.com.
Brut. Sauvage. Imprévisible.
