Cold brew

Cold water extracts acids far more slowly than it extracts sugars and caffeine. Long steeping compensates for the temperature, and the resulting concentrate is low in perceived acidity by chemistry rather than by roast.

Why time replaces temperature

Extraction is a race between compounds, and cold water changes the order. Sugars and caffeine come out steadily; the acids and the aromatic oils that hot water strips in three minutes barely move. Twelve to eighteen hours gets the first group out without ever collecting much of the second, which is why cold brew tastes low in acidity whatever the roast says.

Immersion or slow drip

Immersion is a jar: coarse grounds, cold water, a fridge, a filter at the end. It is forgiving and it is what almost everyone should do. Slow drip, the Kyoto tower, meters cold water through a bed one drop at a time over six to eight hours and gives a cleaner, more tea-like result for a great deal more fuss.

Brew a concentrate

1:5 for the steep, then dilute in the glass. A concentrate keeps its strength when it hits ice, it stores better, and it lets one batch serve a week. Ready to drink cold brew is the same recipe diluted early, which means the ice decides the strength instead of you.

Keeping it

Filtered and refrigerated, a concentrate holds up for about two weeks; it stops tasting fresh well before it becomes unsafe. Never leave the grounds in the liquid after the steep, and never use hot water to rinse the last of it out: the whole point is that no hot water touched this coffee.