Coarsely grind the coffee beans in a coffee grinder until medium coarseness; aim for the size suited for a French press.
Transfer to a 2 L jar and slowly pour filtered water over top; stir well to hydrate the coffee grounds. The coffee grounds will float to the top, make sure all the coffee grounds are wet.
Cover and leave at room temperature for at least 12 hrs.
Place a cheesecloth-lined sieve set over a large measuring cup or bowl; slowly pour concentrated coffee and grounds through the strainer without pressing (this will release bitter oils).
Transfer to a clean jar and refrigerate for up to 7 to 10 days.