How to Make Cold Brew Coffee at Home: 24-Hour Guide

Cold brew coffee sales in the United States grew 26 percent annually between 2015 and 2023, making it the fastest-growing segment in the ready-to-drink coffee category according to Mintel. Yet most cold brew sold in stores costs USD 5 to 9 per 300 ml bottle. The same volume made at home from quality beans costs under USD 0.80. The process requires no equipment beyond a large jar, a fine-mesh strainer, and a coffee grinder. This guide covers every variable that determines quality.

The Single Most Important Variable: Grind Size

Cold brew requires a coarse grind, approximately the same size as raw sugar crystals or coarse sea salt. Fine or medium-fine grinds cause over-extraction in cold water, producing bitterness and a muddy texture that is difficult to filter. If using pre-ground coffee, use French press grind or coarser. A coarse grind also makes filtering significantly easier because the particles do not clog paper filters.

• Correct grind: coarse, similar to raw sugar (1.2 to 1.4 mm particle size)
• Too fine: bitter, muddy, difficult to filter, over-extracted
• Too coarse: weak, sour, under-extracted, watery
• Burr grinder recommended over blade grinder for consistent particle size
• Pre-ground French press coffee is acceptable if no grinder is available

Coffee to Water Ratios: Concentrate vs. Ready-to-Drink

There are two standard ratios for cold brew. A concentrate uses 1 part coffee to 4 parts water by weight (e.g., 100g coffee to 400g water). The resulting concentrate is diluted 1:1 with water or milk when serving, yielding an effective 1:8 ratio in the final cup. A ready-to-drink cold brew uses 1 part coffee to 8 parts water directly and is served undiluted over ice. Concentrate has a longer shelf life of 2 weeks in the refrigerator versus 1 week for ready-to-drink because the higher caffeine and acidity inhibit bacterial growth.

Use filtered water rather than tap water when possible. Chlorine compounds in municipal tap water react with coffee compounds to produce off-flavors that are more noticeable in cold brew than in hot coffee because heat volatilizes chlorine before brewing is complete. The ideal water for coffee brewing has a total dissolved solids (TDS) reading of 150 to 300 mg/L according to the Specialty Coffee Association water quality standard.

Steep Time and Temperature: The 24-Hour Protocol

The standard cold brew steep is 12 to 24 hours in the refrigerator at 4 degrees Celsius. Steeping at room temperature (21 to 24 degrees Celsius) reduces the time to 8 to 12 hours because molecular activity speeds up with temperature, but room-temperature cold brew has a slightly higher acidity level and a shorter shelf life of 3 to 5 days. Room-temperature steeping also carries a small risk of bacterial growth if the coffee-to-water ratio is too low. Refrigerator steeping at 24 hours produces the smoothest, least acidic result and is the safest method.

Filtering and Storage: Two-Stage Method for Clarity

After steeping, filter in two stages for the cleanest result. Stage 1: pour through a fine-mesh metal strainer to remove all large grounds. Stage 2: pour through a paper coffee filter or a double layer of cheesecloth to remove fine particles that cause cloudiness and accelerate spoilage. Do not squeeze or press the grounds, as this forces bitter compounds into the concentrate. Store in a sealed glass jar in the refrigerator. Concentrate keeps for up to 14 days. Ready-to-drink keeps for 7 days. Discard if you notice any sour or fermented odor.

1. Grind coffee coarse and combine with filtered cold water in a jar
2. Seal and refrigerate for 18 to 24 hours without stirring
3. Filter first through metal strainer, then through paper filter
4. Store concentrate in sealed glass jar in refrigerator
5. Serve over ice, diluted 1:1 with water or milk for concentrate
6. Add flavor with vanilla extract (0.5 tsp), cinnamon, or salted caramel syrup

Conclusion

Cold brew success depends on three controllable variables: coarse grind, correct coffee-to-water ratio, and sufficient steep time in the refrigerator. Get those three right and every batch will be smooth, low-acid, and shelf-stable for two weeks. The upfront time is mostly waiting, not working.