Cold Brew Basics: Coffee Steeped in Cold Water
Cold brew is coffee steeped in cold water for a long time. It tastes nothing like hot coffee poured over ice, and the difference comes down to which compounds temperature is able to dissolve.
Temperature decides what dissolves
The chlorogenic acid compounds behind coffee sourness, and some of the bitter compounds, dissolve much more readily at high temperature. In cold water they are extracted far less.
The result is low acidity and little bitterness, with sweetness and the heavier chocolate and nut aromatics standing out instead. That is why cold brew suits people who find coffee acidity difficult.
There is a cost. Bright, lively acidity and delicate floral aromatics do not come out well in cold water. To enjoy what a light roast has to offer, brew it hot.
Immersion versus slow drip
There are two approaches. Immersion means putting coffee and cold water in a vessel, leaving it, and straining. Slow drip, often called Dutch or Kyoto style, lets water fall drop by drop through a bed of coffee.
At home, immersion is overwhelmingly more practical. It needs only a jar and a strainer, and the margin for error is wide. Slow drip needs dedicated equipment and constant attention to the drip rate.
The difference in the cup is smaller than the difference in effort. Slow drip is a little cleaner, but for the same coffee, ratio and time matter far more than which method you chose.
Recipes
You can brew cold brew to drink as it is, or make a concentrate to dilute. Concentrate saves fridge space and lets you adjust with water or milk.
Room temperature or refrigerated
Where it steeps changes the result. At room temperature (20–25°C) extraction is faster, twelve hours is enough, and there is a little more sweetness. Refrigerated at 4°C it runs slower and needs sixteen to eighteen hours, but comes out considerably cleaner.
Refrigeration is safer from a hygiene point of view, since prolonged room-temperature steeping gives microbes an opening. If you do steep at room temperature, do not push far past twelve hours.
Either way, going beyond eighteen hours starts adding bitterness and woody off-notes. People assume longer means stronger and leave it a full day, but past a point it only gets worse.
Straining and keeping
Squeezing the grounds pushes fines and bitterness through with the liquid. Letting it drain on its own takes longer and tastes considerably cleaner.
Straining once through a coarse mesh and again through paper gives a much clearer result. The extra step is worth it.
Keep it sealed and refrigerated. Three to five days is the window where the concentrate holds up; beyond that the acidity turns odd or the whole thing goes flat. Decanting into smaller bottles limits the air exposure.
Choosing beans
Medium to medium-dark roasts work well, because chocolate, nut and caramel notes survive cold extraction.
Light roasts are usable but tend to fall flat once the acidity is suppressed. If you have paid for an expressive single origin, brewing it hot gets you your money worth.
Since each batch takes a day, keeping notes on ratio and steep time pays off quickly. Few methods reward record-keeping as directly.