Cold Brew at Home: Ratios, Time and How to Not Overthink It

Cold brew is the simplest coffee method that people still manage to overcomplicate. The process is: put ground coffee in cold water. Wait. Strain. Drink.

The waiting is the technique. The rest is just not making a mess.

What cold brew is

Cold brew is coffee made with cold or room-temperature water over a long time, usually 12 to 24 hours. It is an immersion method, like a French press, except the water is cold and the steeping time is measured in hours instead of minutes.

Because cold water extracts compounds from coffee much more slowly than hot water, the extraction is selective. Cold water pulls sugars, chocolates, caramel flavors and smooth, round notes efficiently. It extracts less of the bright acids and the bitter compounds that hot water pulls aggressively [1] [3]. The result is a smooth, low-acid coffee that tastes sweeter and less sharp than the same beans brewed hot.

This is not iced coffee. Iced coffee is hot-brewed coffee poured over ice. It has the same flavor profile as hot coffee, just cold. Cold brew has a fundamentally different extraction and a different flavor.

The method

Equipment

You do not need special equipment. You need:

• A jar, pitcher, or any container that holds liquid
• A strainer (fine mesh, cheesecloth, paper filter, or a French press)
• Coffee
• Water
• A fridge (optional for the steeping phase, recommended for storage)

A dedicated cold brew maker with a built-in filter is convenient but not necessary. A mason jar and a pour-over dripper with a paper filter work just as well.

Ratios

For concentrate (dilute before drinking): 1:5 by weight. That is 1 gram of coffee for every 5 grams of water. For a batch, 200 grams of coffee to 1,000 grams (1 liter) of water makes about 800 ml of concentrate.

For ready-to-drink: 1:12 to 1:15 by weight. That is 70 to 85 grams of coffee per liter of water.

The concentrate approach is more flexible. You make it strong, store it, and dilute each glass to your preference with water, milk, or ice. A 1:5 concentrate diluted 1:1 with water gives you roughly 1:10 strength, which is strong. Diluted 1:2 gives you roughly 1:15, which is closer to regular coffee strength.

Grind

Coarse. Like raw sugar or coarse sea salt. The same grind you would use for a French press.

Fine grinds over-extract during a long steep and make the cold brew bitter and muddy. They also make straining harder, because fine particles clog filters and pass through mesh.

Steps

1. Weigh your coffee. Grind it coarse.
2. Put the grounds in your container.
3. Pour cold or room-temperature water over the grounds. Stir once to make sure all the grounds are wet.
4. Cover the container. Leave it at room temperature or in the fridge.
5. Wait 12 to 24 hours. Do not stir again. Do not check on it. Leave it alone.
6. Strain through a fine mesh strainer to remove the large grounds.
7. Filter through a paper filter or cheesecloth for a cleaner cup. This second pass removes fine particles and oils.
8. Store the filtered cold brew in the fridge.

That is the whole process. The active time is about 5 minutes. The rest is waiting.

Room temperature vs fridge

Steeping at room temperature (65 to 75 degrees Fahrenheit) extracts faster. A 12 to 16 hour room-temperature steep is roughly equivalent to an 18 to 24 hour fridge steep. Room temperature produces a slightly fuller body. Fridge steeping is slower but more controlled, and some people prefer the cleaner result.

If your kitchen is warm (above 75 F), steep in the fridge to prevent any risk of the water getting warm enough to change the extraction character.

Timing

12 hours: Light, bright, slightly acidic. Some people like this. Others find it under-extracted and thin.

16 to 18 hours: The sweet spot for most people. Smooth, sweet, full-bodied, with low acidity and good depth. This is where cold brew does its best work.

24 hours: Strong, heavy, very smooth. Approaching the point where over-extraction becomes a risk, especially at room temperature.

Beyond 24 hours: The extraction moves into woody, astringent, harsh territory. The smoothness that defines cold brew starts to disappear. Stop at 24.

Beans

Medium to dark roasts are the traditional choice for cold brew, and for good reason. Cold water is good at extracting the caramel, chocolate, nut and roast-developed flavors that medium and dark roasts emphasize. It is less effective at extracting the bright, fruity acids that make light roasts interesting when brewed hot [1].

Light roast cold brew is not bad, but it often tastes flat, tea-like or one-dimensional. The flavors that justify the premium of a single-origin light roast are the ones cold water does not pull well.

If you want to try light roast cold brew, grind slightly finer (medium instead of coarse) and steep longer (20 to 24 hours) to increase extraction. Expect a different drink than the same beans brewed as a pour-over.

Storage

Filtered cold brew stored in a sealed container in the fridge keeps well for 7 to 14 days. The flavor shifts slowly over time (it gets a bit flatter), but it does not spoil or become unsafe in that window.

Cold brew concentrate keeps longer than ready-to-drink cold brew because the higher coffee concentration acts as a mild preservative. Two weeks for concentrate is reasonable. One week for ready-to-drink is a safer target if you want peak flavor.

Do not store cold brew at room temperature after straining. It will stale faster and can develop off-flavors within a day or two.

Common mistakes

Grinding too fine. This is the most common cold brew mistake. Fine grounds over-extract during a 16-hour steep and produce bitterness that defeats the whole purpose of cold brew. Grind coarse.

Steeping too long. “If 18 hours is good, 36 must be better” is not how extraction works. Beyond 24 hours, you are extracting compounds that taste harsh and woody. Set a timer or a calendar reminder.

Not filtering well enough. A single pass through a coarse strainer leaves fine particles in the cold brew that make it cloudy and silty. A second pass through a paper filter or fine cheesecloth produces a much cleaner cup.

Using bad water. Cold brew is 90 to 95 percent water. If your tap water tastes like chlorine, your cold brew will taste like chlorine. Use filtered water.

Expecting it to taste like iced pour-over. Cold brew and iced coffee are different drinks. If you want the bright, acidic, fruity character of a light roast, brew it hot and pour it over ice. Cold brew is the smooth, low-acid, chocolate-and-caramel drink. They are both good. They are not the same.

Caffeine, heat and your machine. The FDA says up to about 400 mg of caffeine a day is not generally associated with negative effects for most healthy adults; pregnancy, some heart conditions, anxiety, reflux and certain medicines can change that, so check with a clinician if any apply. Steam wands and group heads are hot enough to burn. Unplug and cool a machine before opening or cleaning it, and follow the manufacturer’s descaling instructions.

Related reading: French Press Technique and Ratios | Water for Coffee