Cold brew has a reputation for being forgiving, and it mostly is — up to a point. The trouble usually starts with a single number: the concentrate ratio. One recipe says 1:5, another insists on 1:8, a third tells you to fill a jar and not think too hard about it. Brew all three and you get three very different liquids, one of which tastes thin over ice and another of which flattens a glass of milk entirely. The fix isn't a secret technique. It's understanding what each ratio produces, then diluting on purpose instead of by habit.

The Ratio Is Coffee to Water, by Weight

Every concentrate ratio is written the same way: coffee first, water second, both by weight. A 1:5 ratio means 100 grams of ground coffee to 500 grams of water. Metric makes the arithmetic painless because a millilitre of water weighs a gram. Cups and scoops don't, because a scoop of coarse grounds and a scoop of fine grounds hold different amounts of coffee. A cheap digital scale settles the question in seconds and is the only piece of gear worth insisting on here.

The second thing to understand is that a concentrate is not a finished drink. It's a stock. Somewhere between the brewing jar and your glass, water or milk gets added. So two numbers matter: the ratio you steep at and the ratio you serve at. Recipes that give you only the first one are half a recipe.

Four Ratios Worth Knowing

  • 1:4 — the syrup end. 100 g coffee to 400 g water. Thick, intensely bittersweet, easy to overdo. Good for iced lattes and anything headed for a lot of milk; hard work as a base for black coffee unless you dilute aggressively.
  • 1:5 — the standard concentrate. The most common starting point for good reason: strong enough to survive ice and dairy, forgiving enough to drink with a modest splash of water. If you've never made concentrate, start here.
  • 1:6 — the flexible middle. Slightly lighter body, more clarity, a little more slack on steep time. It suits people who drink most of their cold brew black or with a squeeze of citrus.
  • 1:8 — strong but nearly drinkable. Some people take this straight over ice; most prefer a small top-up. Useful if you want one batch that can go either way depending on the morning.

One caution: yield is lower than the water you pour in. Wet grounds hold on to a good deal of liquid — often close to twice their own weight — so a 100 g batch brewed at 1:5 leaves you with well under 500 ml of concentrate. Plan for it. Weigh your finished concentrate once and you'll know your own number from then on.

Diluting to the Strength You Actually Want

Treat dilution as a dial, not a rule. One part concentrate to one part water gives a bold, almost syrupy cup that still tastes like coffee after it meets a full glass of ice. One to two is the everyday iced coffee most people are chasing. One to three is light and tea-like — pleasant on a hot afternoon, less satisfying if you take milk.

Over ice

Ice melts, and it dilutes whether you planned for it or not. A drink poured at 1:1 over a tall glass of cubes will taste right for two minutes and weak for the next ten. Use large cubes, chill both the concentrate and the water, or simply dilute a little less and let the melt finish the job.

With milk

Milk softens coffee's acidity and mutes its aromatics, so a ratio that tastes punchy black can vanish in a latte. Use a 1:4 or 1:5 concentrate and dilute it 1:1 with cold milk rather than 1:2 with water. Oat milk drinks sweeter than dairy, so go a touch easier on the concentrate with it.

With tonic or sparkling water

Fizz demands brightness. A 1:6 concentrate diluted 1:1 with chilled tonic over ice, finished with a strip of orange peel, keeps the coffee present without turning the drink into a syrup. Skip the sugar syrup unless you like it sweet.

A Worked Recipe, Start to Finish

  1. Weigh 100 g of coffee, ground coarse — roughly the texture of sea salt.
  2. Add 500 g of cold filtered water. Stir gently until all the grounds are wet, then leave them alone.
  3. Steep 14 to 16 hours at room temperature, or 18 to 24 hours in the fridge for a cleaner, slower extraction.
  4. Strain through a fine sieve lined with muslin or a paper filter. Take your time; squeezing the bed hard pushes silt and bitterness into the liquid.
  5. Weigh the concentrate so you know what the batch actually produced. Then dilute to taste: start with 60 ml concentrate and 120 ml water over ice, and adjust from there.

Grind and Time Change the Math

The ratio isn't the only variable, and it isn't even the most influential one. A grind that drifts finer extracts faster, so the same 1:5 batch can turn harsh and drying; a grind that's too coarse leaves you with a woody, hollow cup no amount of extra steeping fully rescues. Time works the same way. Room temperature is quicker and rounder, the fridge is slower and cleaner. If you change your coffee, your grinder setting or the temperature of your kitchen, expect to adjust the ratio slightly on the next batch rather than assuming the old number still holds.

Water matters less than most people think, but it isn't irrelevant. Very hard tap water mutes flavour; heavily softened water tastes flat. Filtered water is a sensible default.

Keep Notes, Not Rules

Write down two numbers for every batch: the brew ratio and the dilution you liked. After three batches you'll have your own house standard, which is worth more than any recipe you find online, because it's calibrated to your grinder, your water and your taste. Store the concentrate covered in the fridge and drink it within about a week — it's at its best in the first few days, and it will dull before it spoils.

Treat concentrate with a little respect, too. Because it's concentrated, a modest-looking serving can carry more caffeine than the same volume of ready-to-drink cold brew, so dilute it as intended and go easy if you're sensitive. Start at 1:5, dilute half and half, then taste and adjust. That single habit will teach you more about cold brew than any ratio chart.

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