Place the coarsely ground coffee in a large jar, jug, or non-reactive container. Pour over the cold filtered water. Stir thoroughly so all of the grounds are fully saturated and no dry pockets remain. Every ground should be wetted at the beginning. If dry clumps remain, extraction will be uneven and the finished brew will taste weak in some areas and muddy in others. A thorough initial stir is worth genuinely confirming rather than assuming — any grounds left clumped together and unsaturated at this stage won't extract at the same rate as the rest of the batch, and that inconsistency shows up directly in the finished cup as an uneven, unpredictable flavour.

Cover the container and let the coffee steep for 12–16 hours in the refrigerator or at a cool room temperature. The brew should become very dark and smell smooth, rich, and chocolatey rather than sharp or acidic. Shorter steeping gives a thinner, weaker result. Much longer steeping can flatten the flavour and pull out woody bitterness. Use a coarse grind, not fine espresso grind. Fine coffee creates sludge, over-extracts, and makes filtering unnecessarily difficult. Cold water extracts coffee's compounds far more slowly than hot water does, which is exactly why this steep needs many hours rather than minutes — that slow, patient extraction is what pulls out the smooth, chocolatey notes cold brew is known for while leaving behind more of the sharp acidity and bitterness a hot brew extracts much faster.

Pour the mixture through a fine mesh sieve lined with cheesecloth, a clean nut milk bag, or a thin clean kitchen cloth into a clean jug or bowl. Let it drain naturally first, then gently press only if needed. The first strain should remove the bulk of the grounds without forcing too much sediment through. Pressing too aggressively pushes fine particles into the brew and makes it cloudy. Letting the liquid drain naturally under its own weight, rather than pressing hard from the start, is what keeps the finer coffee particles trapped in the cloth or sieve rather than being forced through into the liquid — any aggressive pressing at this stage undoes much of the clarity this two-stage straining process is built to achieve.

Strain the coffee again through a paper coffee filter or a very fine clean cloth into a clean serving bottle or jug. This second filtration is what gives the finished cold brew a cleaner, smoother texture. The finished coffee should look dark and clear, not gritty or muddy. Some patience here makes a real difference in the final drink. This second, finer pass catches the small remaining particles that the first strain's coarser mesh inevitably let through — skipping this step leaves a noticeably grittier texture in the finished coffee even if the first strain was handled carefully.

Refrigerate the strained cold brew until fully cold. It can be kept covered in the refrigerator for up to 4 days. Cold brew should be fully chilled before serving. If served only cool rather than properly cold, it tastes flatter and less crisp. Genuine refrigerator-cold temperature sharpens the coffee's clean, smooth flavour in a way that merely cool room-temperature coffee doesn't — the difference is noticeable enough that this step is worth the wait rather than serving straight after straining.

Place 1 large clear ice cube in each glass. Pour the cold brew over the ice and serve immediately. For a classic straight cold brew presentation, serve it black with no milk, no garnish, and no dilution beyond the ice. The drink should be very deep brown to near-black, smooth, and clean-tasting, with the large cube chilling it without watering it down too quickly. A single large cube's low surface-area-to-volume ratio protects the cold brew's concentration and clarity through the time it takes to drink — several smaller cubes with the same total volume would dilute the coffee considerably faster.