Cold brew has a reputation for being forgiving, and in some ways it is. You can steep it too long and it will still be drinkable. You can use a slightly wrong grind and the result will be acceptable. But if you want a cold brew that is genuinely good, the ratio is the variable that matters most, and getting it right requires understanding what you are actually trying to extract.

Why ratio matters more than steep time

Most cold brew guides tell you to steep for 12 to 24 hours and leave the ratio as a secondary consideration. In our testing, the opposite is true. A 1:10 ratio steeped for 12 hours produces a concentrate that is thick, slightly bitter, and loses most of its origin character when diluted. A 1:14 ratio steeped for 16 hours produces a ready-to-drink brew that is sweet, clear, and expressive of the coffee's origin. The steep time is a dial. The ratio is the foundation.

What we use at the roastery

We settled on 1:14 as our standard ratio after testing 1:10, 1:12, 1:14, and 1:16 with the same lot of Guji Natural over four consecutive Fridays. At 1:14, the sweetness from the natural process is fully present, the fruit note is clear without being cloying, and the finish is clean. At 1:12, the body is heavier but the acidity becomes slightly harsh. At 1:16, the cup is pleasant but thin.

Grind size and its effect on cold brew

We grind coarse for cold brew, roughly the same setting as French press. A finer grind increases extraction speed, which sounds efficient, but it also pulls out compounds that contribute bitterness and cloudiness. Cold brew is a slow process by design. Grinding coarse and steeping for 16 hours gives the water time to extract the sugars and acids without over-extracting the bitter compounds.

Refrigerator versus room temperature

Room temperature cold brew extracts faster, typically 8 to 12 hours, and produces a different flavour profile. The extraction is less selective at higher temperatures, which means you get more body but also more bitterness. We prefer the refrigerator method for the Guji Natural because the slower extraction preserves the fruit clarity. If you are using a chocolatey, medium-roast coffee, room temperature can work well.

Which coffees work best for cold brew

Natural process coffees tend to perform well in cold brew because their inherent sweetness compensates for the lower extraction temperature. The Guji Natural and the Acatenango Honey are both good choices. Washed coffees with high acidity, like the Kochere, can taste thin in cold brew unless you adjust the ratio down to 1:12. The Huila Washed sits in the middle and works at 1:13 or 1:14.

Cold brew is worth making at home if you get the ratio right. Start at 1:14 with a coarse grind and 16 hours in the refrigerator, then adjust from there. The Guji Natural is the coffee we reach for every summer morning.