Cold Brew Extraction: The Chemistry of Long, Low-Temperature Brewing

Cold brew is not simply hot brew that has been cooled. The chemistry of extraction at low temperatures is fundamentally different from extraction at high temperatures, and the resulting cup has different flavour characteristics that cannot be replicated by chilling hot-brewed coffee. Understanding why requires understanding how temperature affects the solubility of different coffee compounds.

At lower temperatures, certain compounds — particularly the more volatile aromatics and some of the more bitter compounds — extract much more slowly than at hot temperatures. Other compounds, particularly the sugars and some of the milder acids, extract relatively efficiently even at cold temperatures. The net result is a cup that is less bitter, less acidic, and sweeter than hot-brewed coffee, but with fewer of the bright, aromatic top notes that define freshly brewed hot coffee.

The principle behind cold brew extraction

Cold brew extracts coffee at temperatures where solubility differences between compound classes are exaggerated. The result is a cup with a different chemical composition than hot-brewed coffee — not just less of everything, but a different ratio of compounds. Cold brew is sweeter, less acidic, and less bitter than hot brew, but also less aromatic and complex in the way that hot brew can be.

Three things are easy to confuse here, and separating them saves a lot of wasted coffee. Strength is how concentrated the cup is. Extraction is how much the water pulled out of the grounds. Preference is whether you like the result. A stronger cup is not a better-extracted one, and the recipe a cafe uses is not automatically the recipe your grinder wants.

What most changes the result

Temperature

Cold brew is typically made at refrigerator temperature (4–7 °C) or room temperature (18–22 °C). Room temperature extracts faster but may produce different flavour profiles than refrigerator temperature. The choice depends on time available and taste preference.

Time

12 to 24 hours is standard for cold brew. Shorter times produce thinner, more acidic cups; longer times produce more extracted, potentially more bitter cups.

Grind size

Coarse grind is standard. Fine grinds produce over-extraction and sediment issues.

Ratio

Concentrate ratios (1:4 to 1:8) and ready-to-drink ratios (1:10 to 1:16) are both common. Concentrates are diluted before drinking; ready-to-drink is consumed as brewed.

Coffee selection

Cold brew highlights the body, sweetness and chocolate notes of coffee. It works particularly well with medium-to-dark roasted, full-bodied coffees. It is less suited to delicate, floral, acidic light-roasted coffees, which lose their defining characteristics in cold extraction.

A repeatable starting method

1. Use a coarse grind. Medium and fine grinds produce sediment and over-extraction.
2. Combine coffee and water at your chosen ratio. For concentrate, use approximately 1:4 to 1:8. For ready-to-drink, use 1:10 to 1:16.
3. Steep at refrigerator temperature for 16–24 hours, or at room temperature for 8–12 hours. The exact time depends on the coffee and your preference.
4. Filter the brew through a paper filter or fine mesh strainer. Cold brew produces sediment that affects mouthfeel; thorough filtration produces a cleaner cup.
5. Store the finished cold brew in the refrigerator. It keeps for up to two weeks, though flavour is best within the first few days.

Write down the dose, the water weight, the temperature and the total time, then one honest word for the cup. "Sour", "dry", "thin" and "heavy" are all useful when they describe a specific brew. Change one number and run it again.

The numbers we use

These are the figures behind our own cold brew guidance, and the starting point this article assumes.

When it goes wrong

• Weak and watery — Diluted too far, or steeped too briefly Dilute less. Remember the strained liquid is concentrate.
• Woody or flat — Steeped too long Stop at 16 hours.

Worth knowing: Caffeine and serving strength vary with dose, preparation, and individual sensitivity.

Common mistakes

• Brewing at room temperature for too long. Extended room-temperature brewing can produce off-flavours and, in rare cases, harmful bacterial growth.
• Assuming cold brew is automatically less acidic. It has lower titratable acidity at the same pH, which is a different claim. People with GERD may find it easier to tolerate; others may not.
• Using cold brew as a substitute for hot-brewed coffee. The flavour profiles are different; cold brew is not "the same" coffee cooled.
• Brewing fine grind coffee at cold temperatures. Fine grinds produce over-extraction and sediment issues at any temperature, but the problems are more pronounced in cold brew.

How to choose your next adjustment

Use cold brew for a sweeter, less acidic, less bitter cup with full body. Brew for 12–24 hours at refrigerator temperature with a coarse grind. Filter thoroughly. Cold brew is a different product from hot brew, not a substitute; appreciate it for what it is.

One caveat on caffeine: brewing method and roast colour tell you very little about the dose. A large cold brew can carry several times what a single espresso does. Use the figure for the specific product rather than for the category.

Related on CupCura

• Cold Brew and Vanilla Dessert
• Lion's Mane Iced Cold Brew
• The brewing guide and timer
• The equipment guide

Frequently asked questions

What should I change first with cold brew extraction?

Temperature. Cold brew is typically made at refrigerator temperature (4–7 °C) or room temperature (18–22 °C). Room temperature extracts faster but may produce different flavour profiles than refrigerator temperature. The choice depends on time available and taste preference.

What is the most common mistake?

Brewing at room temperature for too long. Extended room-temperature brewing can produce off-flavours and, in rare cases, harmful bacterial growth. It is worth ruling that out before changing anything else, because it makes every other adjustment harder to read.

Does coffee selection matter?

Cold brew highlights the body, sweetness and chocolate notes of coffee. It works particularly well with medium-to-dark roasted, full-bodied coffees. It is less suited to delicate, floral, acidic light-roasted coffees, which lose their defining characteristics in cold extraction.

How many brews before I judge a coffee?

Two or three. One uneven bed or a mistimed pour can misrepresent a good roast, and three careful attempts is enough evidence that it simply is not to your taste.

Sources

• Rao NZ, Fuller M. Acidity and antioxidant activity of cold brew coffee. Sci Rep 2018; 8: 16544 — cold brew chemistry; Food Chemistry 2019; 286: 188–195 — extraction kinetics at low temperature.