What Is Cold Brew Coffee? Why Temperature Matters, Not Time

Cold brew is coffee steeped in cold or room-temperature water for a long period, usually 12 to 24 hours, then strained, and it is an immersion method like a French press run very slowly.

No heat is applied at any stage, which is the definition and what separates cold brew from every method that uses heat.

Cold brew at a glance

Method

Immersion, with the grounds sitting in the water throughout

Heat

None at any point, which is what the name describes

Grind

Coarse, roughly like sea salt

Usual ratio

1:5 for a concentrate, about 1:12 for a ready-to-drink brew

Steep

12 to 16 hours at room temperature, 18 to 24 in the fridge

Keeps

Seven to ten days refrigerated as concentrate

Caffeine

Not low. Caffeine dissolves readily even in cold water

What cold water leaves behind in the grounds

Temperature governs which compounds dissolve and how quickly, and cold water turns out to be selective in a way hot water is not. Some of what makes hot coffee taste like hot coffee needs heat to become soluble at all, so it stays in the grounds and goes into the bin with them.

What cold water extracts, and what it leaves

Caffeine

Dissolves readily even cold, so cold brew is not low in caffeine

Sugars

Dissolve well, which is why it tastes sweet

Chlorogenic acids

Tend to extract less, which softens the perceived acidity

Bitter compounds

Largely left behind, since many need heat to become soluble

Aromatics

Muted. The volatile compounds that make hot coffee smell vivid stay put

Cold brew tastes sweet because the sugars come through while fewer of the acids and bitter compounds that would balance them do, so the same coffee reads as sweeter than it does hot.

Two very different coffees brewed this way land closer together than you would expect, because the method accounts for much of the flavour. The full sensory picture is set out in how cold brew tastes.

Concentrate, dilution and the steep window

Almost every cold brew recipe is written for a concentrate rather than a drink, and that single convention accounts for most of the confusion around its ratios.

Concentrate, then dilution

Coffee

100 g coarse ground

Water

500 ml cold

Ratio

1:5 for a concentrate

Steep

12 to 18 hours at room temperature, or up to 24 in the fridge

Strain

Through a fine filter or cloth

Serve

Dilute 1:1 to 1:3 with water, milk or ice

A 1:5 brew is a concentrate, not a drink, and tasting it neat is the most common first-attempt mistake. If you would rather skip the dilution step entirely, brew at around 1:12 and pour it straight, at the cost of taking up about two and a half times the fridge space for the same amount of coffee.

The sequence for either version is in making cold brew.

What happens as the steep runs longer

UnderOver

1. Under 8 hoursThin, sour, obviously under-extracted
2. 12 to 16 hoursThe usual window at room temperature
3. 18 to 24 hoursThe fridge window. Fuller, still clean
4. Beyond 24 hoursWoody and papery notes appear
5. Beyond 36 hoursFlat and dull, with no gain in strength

Room temperature and refrigeration are two settings of the same dial. A warmer steep extracts faster and gives a fuller, slightly heavier cup in 12 to 16 hours, while the fridge is slower and cleaner and wants 18 to 24.

Leaving either one longer adds little.

Coarse grind, and why you strain it twice

Grind size does different work here than in hot brewing, where it sets the speed of extraction. Over twelve hours or more, almost everything soluble comes out regardless, so the grind is really deciding how much sediment you have to remove at the end and how much bitterness the fines contribute while they sit there.

Coarse is standard, roughly like sea salt and if anything coarser than for a French press. A fine grind over eighteen hours over-extracts, and more practically it turns straining into a slow, silty job that ends with fines in the bottle.

Two-stage straining is what separates a clean batch from a silty one: the first pass removes the bulk, the second removes the fines that would otherwise keep extracting in the bottle for the rest of the week.

Let it drip through under its own weight, however long that takes. Pressing the filter to speed it up is exactly what pushes the fines you were trying to remove into the carafe, and the same instinct spoils a pour-over for the same reason.

Cold brew, iced coffee and the Japanese method

These three get used interchangeably on menus and they are different drinks made in different ways.

Japanese iced coffee is the interesting one, because it solves the problem cold brew creates. Brewing hot directly onto ice, with that ice counted as part of the brew water rather than added afterwards, gives a cold cup that keeps the aromatics hot brewing produces and loses none of them to standing time.

Japanese iced coffee, roughly

Coffee

20 g, medium grind

Ice in the carafe

150 g, weighed as part of the water

Hot water poured

200 g

Total brew water

350 g, of which the ice is part

Result

Bright, aromatic, and cold within seconds of brewing

If you find cold brew flat and want something bright and cold, the answer is a different method rather than a different recipe. No adjustment to a cold steep will put back aromatics that were never extracted, and the comparison with plain chilled coffee is set out in iced coffee.

Nitrogen, and why it reads as creamy

The nitro version is worth understanding because it changes the texture of the drink without changing a single thing about how the coffee was made.

Nitro is cold brew infused with nitrogen and dispensed under pressure through a restrictor plate. Nitrogen dissolves poorly in water, so it comes out of solution almost immediately as very fine bubbles rather than the sharp prickle carbon dioxide gives, and those bubbles are small enough to hold together as a foam instead of breaking at the surface.

You get a cascading pour, a dense head, and a mouthfeel that reads as rounder and sweeter than the same coffee poured flat. Nothing has been added and the whole difference is physical, so nitro tastes creamy without the steamed milk a latte needs to get there, and nitro coffee is treated as its own drink rather than a serving style.

Ten days in the fridge, and what shortens it

Cold brew concentrate keeps longer in the fridge than a hot brew does, and that is a large part of why it exists on menus at all.

Concentrate holds seven to ten days refrigerated in a sealed container, against hours for a hot brew. Once you have diluted it, cold brew is a different proposition and is closer to two or three days before it goes flat, since the water it was cut with brings nothing that preserves it.

Cold brew needs refrigeration from the moment it is strained. Keeping it in the container it was strained into, rather than decanting, limits contact with oxygen, which is a slow spoiler of flavour.

Timescales for both concentrate and diluted are set out in storing cold brew.

Which roasts survive the method

Cold brew flatters some coffees and quietly wastes others, and the pattern is consistent enough for you to shop by.

Medium and medium-dark roasts suit it best, because the chocolate and nutty notes they carry come from the roast rather than from the fruit acids, and roast character extracts perfectly well in cold water.

Light, bright, fruity coffees are largely thrown away here. The acidity and floral aromatics that justify their price tend to be what cold extraction leaves behind, so an expensive Ethiopian ends up tasting closer to a cheaper Brazilian.

How well each roast suits cold brew

BestWorst

1. Medium-darkChocolate and nut notes survive cold extraction intact
2. MediumThe safe default, and what most commercial cold brew uses
3. DarkWorks, though ashy notes come through more than expected
4. Light, washedThin and flat. The acidity that carried it is gone
5. Light, fruity single originThe most wasted. Pay for it and brew it hot

Cold brew is the method to use up good-but-not-special coffee, and the wrong place to spend money on a delicate single origin. A little robusta in the blend is less of a liability than usual, since the heavy body it brings is welcome and the harshness it can bring extracts less fully.

Freshness matters less than for espresso, since aromatics play a smaller role from the start.

A jar, a sieve, and the habits that separate batches

Almost nothing here requires a purchase, which is unusual in coffee and is a fair part of the appeal.

A large jar, a sieve and a paper filter produce results equal to any dedicated device, and the case for a purpose-made cold brew maker is convenience rather than quality. What actually separates a flat batch from a good one is a short list of habits.

• Weigh the coffee and the water, since the ratio is the whole recipe.
• Wet all the grounds at the start and stir once; dry pockets never extract.
• Steep at room temperature rather than in the fridge for a fuller result.
• Strain twice, and never squeeze the grounds.
• Dilute to taste at serving rather than storing it pre-diluted.

Storing it concentrated and cutting each glass as you pour is the single most useful of those. It keeps longer, takes less fridge space, and lets the same batch serve as a small strong glass in the morning and a long milky one in the afternoon.

Dilution, and what each gives

StrongestWeakest

1. Undiluted concentrateToo strong to drink. Use for cooking or affogato
2. 1:1 with waterVery strong, closer to a long espresso
3. 1:2 with waterThe usual serving strength
4. 1:3 with water or milkMild, and the common café iced-latte base
5. Over ice onlyDilutes as it melts, so it starts strong and finishes weak

Work down that list once with a single batch and you will know your own preference, which no published recipe can tell you.

What concentrate is good for besides a glass of it

Concentrate is more versatile than a jug of ready-to-drink coffee, because it adds coffee flavour without adding much liquid, and several of its uses have nothing to do with drinking it cold.

That last one surprises people and is worth trying before you dismiss it. Cold brew let down with hot water is a perfectly good hot drink that keeps the low acidity the method was chosen for in the first place.

Food pairings follow the same logic and are not the ones that suit hot coffee. Acidity is what lets a hot cup cut through fat and pastry, and cold brew tastes much less acidic, so it sits alongside rich food rather than slicing into it.

Sweetened, it wants a liquid sweetener rather than granulated, since there is no heat in the glass to dissolve anything, and simple syrup exists largely for this problem.

Strong in two different senses

Anyone making cold brew for the first time tends to hit the same two surprises, and both come from the same place.

The first is how strong the concentrate is. A 1:5 brew tasted neat is close to undrinkable and you conclude that you have made it wrong, when it is behaving exactly as intended.

The second is how little it smells. There is less aroma over the glass than over a hot cup, because cold water extracts fewer of the volatile compounds that produce that smell.

The word strong is doing two jobs here, and they pull in opposite directions: concentration is how much dissolved coffee sits in the liquid, whereas extraction is how much was pulled out of the grounds.

A 1:5 cold brew is very high on concentration and genuinely low on extraction, which is why it tastes intense and smooth at the same time.

Diluting it therefore does not make it weak the way an under-brewed hot coffee is weak. It makes it less concentrated while keeping the same low-extraction character, and the caffeine that came with it is untouched.

Why cafes adopted it, and what the method costs the coffee

Cold brew went from niche to standard in about a decade, and the reasons were commercial at least as much as they were about taste.

For a café it can be made entirely in advance, held for a week and served in seconds with little barista skill involved. For a drinker the low acidity and natural sweetness make it approachable without milk or sugar.

What the method costs is clarity of origin. Cold brew is the least demanding preparation here on the coffee itself, since twelve hours of contact extracts plenty from beans that would brew flat and hollow hot, and by the same token an expensive single-origin arabica is mostly wasted on it.

On strength it is also the most misleading: a ready-to-drink bottle can carry more caffeine than a filter coffee at a similar volume, which caffeine by brew method places against the other preparations and cold brew caffeine works out per glass.

When your batch comes out wrong, the cause is usually the grind or the strain rather than the beans, and cold brew problems sorts one from the other.