A no-nonsense recipe for cold brew

30 Oct, 2023

When I was first starting to make cold brew at home I had trouble finding a proper recipe to do it. Pretty much all websites that Google suggested were crappy marketing sites where the recipe was buried in a quagmire of useless content and ads. And those recipes I did find where always of the form "making cold brew is easy, just add your favorite coffee and water, leave for a day and then strain", which is something any person can infer and doesn't really tell you anything.

I eventually stumbled on some Reddit comments¹ explaining the process, and after doing some experimentation I think I have a good process going. I wanted to share it here to help other people like me, who wanted to do it but are not sure how. Trust me, it's really easy.

What you'll need

• A big-ish container. Anything works.
• Something to strain your coffee. I use a normal coffee strainer, but also a French press would work.
• Coffee. In my experience it doesn't matter much if you use a coarse or fine grind, or an expensive or cheap coffee. Personally I use a cheap medium roast fine grind, mainly because it's easily available. You'll need at least 2 cups of coffee.
• Measuring cups are great to have if you care about correctness.

Brewing

Ratio: 1:8 ratio by weight. According to my measurement that's 1 cup of ground coffee for every 3.5 cups of water.

Fill your container with as many repetitions of the ratio as you want (or as many as fit in your container). Then leave in the fridge for 24h. Some people leave it outside at room temperature, and some leave it for 12h, but I like fridge+24h because the end result tends to be less bitter.

Serving

tl;dr - For each serving: 7 tablespoons (a bit less then half a cup) of concentrate + 1 (or 1.5) cup of water

This part is something that "guides" never mention. The most I've found are some vague instructions like serve 1:1 or 1:2 ratio of concentrate and water. This sounds good enough I guess, but for someone who is sensitive to caffeine as I am it's better to know how much caffeine is in your cup, unless I want to be miserable for the next 8 hours or so as the coffee courses through my body.

Let's do some quick math. When preparing coffee in a French press I use 2 tablespoons of coffee, any more than that and I get the jitters, so I'll be aiming at getting the same amount from cold brew (you can adapt as needed). If we brew two ratios then we'll use 2 cups of coffee and 7 cups of water while extracting. So there would be 16 tablespoons of coffee per cup in the concentrate, meaning that there are a total of 32 tablespoons.

To make things easier, the 7 cups can be equated to 112 tablespoons. Assuming dissolution of caffeine is uniform (and I think we CAN assume it because caffeine is easily soluble in water), there are 32/112=0.285 tablespoon-worth's of caffeine per tablespoon in the concentrate.

That means that when I serve my cup, if I want 2 tablespoon-worth's of caffeine then I need to serve 0.285*x=2 which is ~7 tablespoons of concentrate (a bit less than half-a-cup).

So that's it for the amount of concentrate to serve, but what about the amount of water? Well, that really depends on your taste. I personally like a bigger cup even if the flavor is more diluted so I'll add 1.5 cups of water.