I was interested today in making some cold brew. I have a french press so I'd like to use that.
What is your recommended brewing time? Does this make a concentrate? What ratio do you use later to dilute that concentrate?
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First, make sure to study What do I need to start cold-brewing. But since concentrate is not discussed there, I don't think your question is a duplicate. Your French press concentrate could last a couple days, depending on the consumption.
Assuming you divide the volume of the French press by 5, you would need 1 part of ground coffee (the usual coarse grind you use in the press; extraction is weaker at low temperatures but the time makes up for it even with coarse grind) and 4 parts of fresh room-temperature water, which you gently mix and stir. The coffee should sit for about 12-16 hours at room temperature. Then plunge, and here is the concentrate. To dilute, use another 8 parts of cold water or milk (or better, start with 5-6 parts and taste to determine whether you want it still thinner).
Here's my favourite article that discusses dripping methods as well.
The standard recommended ratios for cold brew are:
| Roaster | oz Coffee | oz water | time | ratio |
|Stumptown | 12oz | 56oz | 16 hours | .214 |
|Blue Bottle | 16oz | 67.6oz | 12 hour | .236 |
|Ritual | 4oz | 35.2oz | 18 hours | .113 |
|Intelligentsia | 8oz | 56oz | 12 hours | .142 |
These recipes vary in concentration - the lower ~0.1 recipes are designed to be consumed without dilution, while the ~0.2 recipes are designed to be consumed in a 1:2 cold brew concentrate to water dilution.
17:1 water to coffee ratio (by weight) for regular coffee
4:1 ratio for cold brew
The extraction will also be impacted by things like grind size, water temp & dwell time so in order to get a "golden cup."
Image from SCAA