How to Make Cold Brew at Home: Ratio, Grind and Steep Time ☕

"Mine always comes out bitter, or it tastes like brown water," a customer told the barista while we waited in line for a refill. Homemade cold brew usually fails in one of four ways, and each one leaves a sign you can taste.

Here is what you get: a starting recipe with ratio, grind and steep time, a quick way to diagnose a bad batch, and how long a jar keeps in the fridge.

The starting recipe

This makes a concentrate; America's Test Kitchen uses nearly the same proportion.

Quick triage

• Taste a diluted sip: thin and empty, or harsh on the finish?
• Look at the bottom of the glass. Silt means a filtering problem.
• Check the jar date. A good batch that went dull is a storage problem.

Cause and cure

Weak or watery

Sign: tastes like coffee-flavored water. Why: too little coffee, too coarse a grind, or dry clumps that never got wet. Fix: raise the coffee dose by about 10 to 15 percent and keep the steep time the same; go one grind step finer only if it is still thin.

Bitter or woody

Sign: a harsh, drying finish. Why: the grind is too fine or the steep ran long; past 48 hours, woody notes take over. Fix: coarsen the grind one notch, then cut the steep by two hours if needed.

Sour and thin

Sign: sharp and hollow in the cup, with no sweetness behind it. Why: under-extraction; cold water works slowly, and a short steep or a cold fridge leaves flavor behind. Fix: add two hours, or steep on the counter instead of in the fridge.

Muddy or silty

Sign: cloudy coffee and a gritty last sip. Why: fine particles slipped through. Fix: strain through mesh, let it rest 5 to 10 minutes so the fines settle, then pour slowly through paper. Do not squeeze the grounds or the bag; that pushes sediment straight into the jar.

Hidden tip: stir twice. Coarse grounds float and form a dry raft on top. America's Test Kitchen stirs, waits about 10 minutes, then stirs again so every particle is wet. That alone rescues many weak batches.

Hidden tip: "less acidic" is mostly about taste. A 2018 study in Scientific Reports found cold and hot brew had similar pH; the hot brews held more titratable acids, which is why cold brew tastes softer, not because it is far less acidic.

How long it keeps, and when to toss it

Keep concentrate sealed in the fridge and label the jar with the brew date. America's Test Kitchen gives it up to a week; brewer makers such as ESPRO say up to two weeks. Taste before you pour. If it smells sour or off, or anything grows on the surface, pour it out; no recipe tweak saves that batch.

Keep the next batch on track

• Weigh coffee and water instead of scooping.
• Write ratio, grind and hours on the jar label.
• Dilute only what you are about to drink.

I log batches the same way in my cupping notebook; adjust one variable per batch and the pattern shows fast.

Cheat sheet: cold brew at home

Diagnosis in one line: bitter means too far, sour means not far enough. Adjust one variable, then taste again.