Brewing

Ratio, grind, water temperature, contact time and the water itself — what each one changes in filter coffee, and a sensible place to start.

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Coffee Rue Journal
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Drawing seen from above. A cone filter on a carafe, water poured in a spiral, and a kitchen scale beside it.

A good filter coffee comes from a handful of variables working together: the ratio of coffee to water, grind size, water temperature, contact time and the water itself. Whatever your equipment or taste, the five are the same. The Specialty Coffee Association (SCA) brewing standard gives a numerical starting point for them. After that, you taste and change one thing at a time.

Ratio: the easiest and most effective lever

The SCA "Golden Cup" standard recommends 55 grams of coffee per litre of water, with a tolerance of 10%. That works out at roughly 1 to 18, or between 50 and 60 grams per litre once the tolerance is included.

Brewing water Suggested coffee (55 g/L) Range with tolerance
250 ml about 14 g 12.5–15 g
500 ml about 27.5 g 25–30 g
1 litre 55 g 50–60 g

The water here is what you brew with, not what ends up in the cup. Weighing on a scale instead of using spoons makes the result far easier to repeat.

Ratio drives how strong the coffee is. In sensory studies at UC Davis, brew strength — the share of dissolved material in the cup — was the biggest single driver of differences in flavour. So if your coffee is balanced but too strong or too weak, the ratio is the first thing to adjust.

Grind and contact time

How long water and coffee stay in contact, together with grind size, sets the extraction. For filter (drip) brewing the SCA suggests 4–6 minutes of contact; 1–4 minutes for finer grinds and 6–8 for coarser ones.

In practice the two are best treated together. Finely ground coffee lets water through more slowly, which lengthens contact time on its own. Our guide to grind size covers how grinding affects flavour in more detail.

Water temperature

The SCA recommends water at 94 °C, plus or minus 2 °C — so 92 to 96 °C — at the point where it meets the coffee.

There is an interesting finding here. In a UC Davis study published in Scientific Reports in 2020, researchers brewed drip coffee at 87, 90 and 93 °C, adjusting grind, ratio and flow at each temperature to hit the same strength and the same extraction. With strength and extraction held constant, the temperature difference across that range had no appreciable effect on flavour.

That doesn't make temperature irrelevant. Temperature affects how quickly material is extracted. But it suggests its main influence works through extraction. If your water is a little cooler, a slightly finer grind or a slightly longer contact can get you to the same place. Keep in mind the study used one brewing method and one coffee.

A spiral pour that wets all of the coffee. A short, silent loop you can pause.

Agitation and wetting

The SCA lists a less discussed variable too: the movement of water as it flows through and around the particles. The aim is for all of the coffee to be wetted evenly, so that material comes out at a similar rate everywhere. When brewing by hand, that means pouring so the whole bed gets wet and no dry pockets are left.

The water itself

Most of a cup of coffee is water, and what is in the water affects brewing. The SCA notes that its brewing standard only holds when the water meets the association's water quality criteria. Those criteria go beyond the scope of this guide, but it is reasonable to assume that water you don't enjoy drinking won't taste better in coffee.

A route for your first brew

If you want to turn the framework into a recipe, here is one way to begin:

  1. Weigh the water you will brew with and measure the coffee at 55 grams per litre.
  2. Grind to a medium size for filter brewing, just before you brew.
  3. Bring the water to 92–96 °C.
  4. Pour so that all the coffee is wetted, and aim for a total contact time of around 4–6 minutes.
  5. Taste. Then change just one variable and compare on the next brew.

While tasting, the UC Davis map can guide you: sourness rises with strength and falls as extraction increases, bitterness climbs with both, and sweetness comes forward when both are low. These findings come from the coffees the researchers tested; yours, and your palate, may behave differently.

Strength, extraction and flavour: a map of trends The horizontal axis is extraction, the vertical axis is brew strength. Sourness rises with strength and falls as extraction increases, so it stands out at the top left. Bitterness rises with both and stands out at the top right. Sweetness stands out when both are low, at the bottom left. Sourness stands out Bitterness stands out Sweetness stands out Extraction Strength (TDS)
A schematic of trends seen in UC Davis sensory studies (Frost et al., SCA News). It shows directions, not values, and is based on the coffees the researchers tested.

Keeping the coffee fresh matters as much as any of these variables; see our guide to storing beans.

Sources