ICold Brew

What the research says about your jar.

Five questions home brewers ask, each answered from published studies. Every file re-plots the numbers, then lists what the studies left out.

How the Lab picks and reads its sources

  1. Does grind size matter for cold brew?

    In a filter bag, coarse grounds extracted about twice as much as medium. Caffeine barely cared about grind, and switching beans mostly moved acidity.

    7.06 %Extraction yield, medium grind (Huila, 14 h)Cordoba et al. 2019

    Illustration of a conical burr coffee grinder in exploded cutaway, showing its hopper of beans, burrs and motor, with a pile of coarse grounds, a pile of finer grounds and two whole beans in front of it.

  2. How long should cold brew steep?

    Caffeine levels off around 6–7 hours at room temperature. Dissolved solids keep climbing, and in one tasting, 14 hours beat 22.

    6–7 hCaffeine and 3-CGA level offFuller & Rao 2017

    Illustration of a single coffee ground, greatly magnified and cut open to show its porous interior, releasing an amber cloud of dissolved coffee into clear water, with a few smaller grounds floating nearby.

  3. What actually changes between cold brew and a French press?

    At room temperature, 8 hours matched the French press for strength and caffeine, with higher pH and less titratable acid. The fridge brew came out weaker.

    2.95 % TDSStrength, room-temp cold brew (23 °C, 8 h)Wang & Lim 2023

    Illustration of a glass French press with its plunger raised beside a clamp-top glass jar of steeping cold brew, both in cross-section with loose grounds suspended in the coffee, steam above the press and a thin frost line on the jar.

  4. How long does cold brew last in the fridge?

    No study sets a safe limit for home cold brew. In sealed lab bottles, bacteria stayed out for 6 weeks while sour, stale flavors crept in.

    <25 CFU/mLBacteria at every check, days 0–42Lopane et al. 2024

    Illustration of a refrigerator door shelf in cutaway, holding a clear swing-top bottle and a clamp-top glass jar of cold brew, with faint lines of cold air drifting past them.

  5. Is cold brew actually less acidic?

    By pH, barely. It stays within about half a unit of hot coffee. By titratable acidity, yes, lower in every coffee tested in both studies.

    4.85–5.13pH, hot and cold (six coffees)Rao & Fuller 2018

    Illustration of two clear glasses side by side: hot black coffee with a wisp of steam on the left, cold brew over large ice cubes on the right, with a few roasted coffee beans between them.