The Science of Smoothness
The fundamental difference between hot coffee and cold brew lies in the extraction process. Hot water, typically between 90°C and 96°C, is an aggressive solvent. It rapidly pulls a wide range of compounds from the coffee grounds, including the desirable
oils and sugars, but also the less desirable ones like certain acids and bitter tannins. This high-heat, fast-paced extraction is what can give hot coffee its sharp, acidic bite. Cold brew, on the other hand, is a game of patience. By using cold or room-temperature water over a period of 12 to 24 hours, the extraction is slow and selective. This gentle process extracts fewer of the acidic compounds, like chlorogenic acids, which are highly soluble in hot water but much less so in cold. As a result, cold brew is chemically less acidic—some studies suggest up to 70% less—making it smoother on the palate and gentler on the stomach.
Why Coarse Grind Is Crucial
For cold brewing, the grind size of your coffee beans is not a minor detail; it is the foundation of a successful brew. Because you are replacing heat with time, the surface area of the coffee grounds becomes critically important. A coarse grind, resembling the texture of raw sugar or sea salt, is universally recommended. The larger particles ensure that the water extracts flavour slowly and evenly over the long steep. If the grind is too fine—like the powder used for espresso—the massive increase in surface area would lead to over-extraction. This would quickly turn your brew bitter and create a sludgy, cloudy concentrate. A coarse grind, however, allows the water to gently pull out the sweet, chocolatey, and nutty flavour notes while leaving many of the bitter compounds behind. It also makes the final filtering process much cleaner and easier, preventing sediment from ending up in your cup.
Your Simple Home Brewing Guide
One of the best parts about cold brew is that you don’t need any fancy or expensive equipment. All you truly need is a large jar or pitcher, coarsely ground coffee, filtered water, and a way to strain it. Start with a basic ratio of coffee to water, typically between 1:5 and 1:8 by weight. A good starting point is about one part coffee to eight parts water. Simply combine your coarse coffee grounds and cold, filtered water in your jar. Give it a gentle stir to ensure all the grounds are saturated. Then, cover the container and let it steep. You can leave it on your countertop at room temperature or place it in the refrigerator. The ideal steeping time is anywhere from 12 to 24 hours; starting with 18 hours is a safe bet.
Filter and Store for the Week
Once your coffee has finished steeping, the final step is to separate the liquid concentrate from the grounds. You can do this by slowly pouring the mixture through a fine-mesh sieve, a coffee filter, or even a clean cheesecloth. The goal is to get a clean, grit-free liquid. Be patient during this stage, as it can take a few minutes for all the liquid to filter through. The resulting liquid is a coffee concentrate, which is stronger than a typical hot-brewed coffee. Store it in a sealed container in the refrigerator, where it will maintain its flavour for up to a week. This 'brew once, drink all week' convenience is another major advantage of the method. When you're ready for a cup, simply dilute the concentrate with water, milk, or a milk alternative. A common dilution ratio is one part concentrate to two or three parts water, but you can adjust it to match your preferred strength. Serve it over ice for a classic, refreshing cold brew.
