How to make cold brew concentrate that keeps

The ratio and grind

Making a cold brew concentrate that retains its clean, punchy character for up to two weeks requires a deliberate departure from standard hot brewing parameters. Where you might use a standard 1:16 brew ratio for your everyday drip brewer, a true concentrate demands a much tighter relationship between water and coffee. We use a 1:4 ratio by weight — for example, 250 grams of coffee to 1000 grams of water. This produces a dense, viscous liquid that acts as a versatile base, ready to be diluted with water, milk, or ice when you are ready to drink.

The size of your ground coffee is the next critical variable. You want a texture resembling coarse sea salt or cracked peppercorns. If your grind is too fine, the water will over-extract the bitter elements during the long steep time, and the microscopic particles will clog your filter, leaving a muddy layer at the bottom of your jar. While fine adjustments are crucial when dialing in espresso, cold brew is incredibly forgiving of minor particle variations. Just aim for consistency and avoid anything resembling sand or powder.

Steeping and filtration

To begin the steep, combine your grounds and cold, filtered water in a large glass jar or dedicated brewing vessel. Stir gently with a long spoon just until all the dry spots disappear; there is no need to agitate the mixture violently. Once the grounds are fully saturated, seal the container. You can leave the jar on your kitchen counter at room temperature for 12 to 16 hours, or place it in the refrigerator for 18 to 24 hours. The colder environment slows down extraction, yielding a slightly sweeter, gentler cup, though both methods produce excellent results.

When the time is up, the filtration phase begins. First, pour the mixture through a fine metal mesh strainer to remove the bulk of the wet grounds. This primary pass prevents the paper filter in the next step from clogging instantly. Next, pass the liquid through a standard paper basket filter or a damp cloth filter set inside a funnel. Do not squeeze the grounds in an attempt to wring out every last drop; as one local roaster warns, “squeezing the filter coaxes out the bitter, dusty sediment you worked so hard to avoid.” Let gravity do the work, even if it takes a few extra minutes… the clarity of the final concentrate is well worth the patience.

Storage and shelf life

The secret to longevity lies in minimising oxygen exposure. Transfer your finished concentrate immediately into clean, glass bottles with tight-fitting swing tops or screw caps, filling them close to the top to leave minimal headspace. The principles of storing coffee beans dictate that they should remain in a cool, dark environment, and the same logic applies to your liquid concentrate. Kept inside a cold refrigerator, the sealed concentrate will retain its vibrant flavor profile for a solid fourteen days without tasting flat or stale.

A jar of this concentrate in your refrigerator functions as an excellent emergency coffee stash for busy mornings when you do not have time to boil water. When you are ready to serve, simply mix one part concentrate with one part boiling water for a quick hot cup, or pour it over ice with equal parts cold water or milk. Because the concentrate is highly stable, you can easily scale up the recipe to brew larger batches, ensuring you always have a reliable, smooth caffeine source on hand for the weeks ahead.