Cold brew looks simple: just add beans to water and put it in the fridge. But whether the strength is right depends entirely on two sets of parameters: the coffee-to-water ratio and the steep time. Once you dial these in, you can produce cold brew consistently to your own taste.

The coffee-to-water ratio determines the base strength. Common cold brew ratios range from 1:10 to 1:13. 1:10 is on the strong side, with a high-concentration cold brew liquid that is a bit heavy to drink straight; it works well diluted with ice water, mixed with milk, or used as a base for specialty drinks, and one batch can make several servings. 1:13 is a regular strength; after steeping, pour it straight over ice for a moderate mouthfeel with balanced sweetness and body. If you prefer something lighter, you can go to 1:15, which gives a lighter flavor and suits people not used to strong coffee. For a first attempt, start at 1:12, then fine-tune based on your preference after tasting it.

Steep time affects the degree of extraction. Cold water extracts slowly, generally requiring twelve to sixteen hours. Too short a time means insufficient release of flavor compounds, leaving the coffee weak with pronounced fruity acidity; too long a time tends to extract excessive bitter compounds, making the mouthfeel bitter and astringent. A medium-coarse grind paired with around fourteen hours is a fairly reliable combination. It is worth noting that different beans extract at slightly different speeds: light roasts have a dense structure, so you can extend the time appropriately; dark roasts are porous, so too long a time easily causes over-extraction, and you can shorten it slightly.

Temperature also plays a role in adjusting strength. The low temperature of refrigerator chilling (around 4°C) extracts more slowly and gives a cleaner flavor; steeping at room temperature extracts faster but requires more precise time control, otherwise it easily brings out astringency. For consistency, most people choose to put it in the fridge overnight and filter it the next day to drink, which is effortless to do and gives controllable results.

The filtering step also affects the mouthfeel. After steeping, filter with filter paper or a fine mesh to completely separate the coffee grounds and fine particles. The cold brew liquid can be stored sealed in the fridge for three to five days, ready to take out and drink whenever you like. Record the coffee-to-water ratio, time and temperature into your own parameter chart, and after making it several times in a row, you will find the set of numbers that best suits your taste, so that every future batch of cold brew comes out right the first time.