In a food processor, pulse the coffee beans until you have a coarse grind. If you don't want to grind your own beans, you can always start with already ground beans.
Pour the coffee grounds into a large pitcher or bowl, then pour 4 cups of water over it, saturating all of the beans.
Let the mixture sit for at least 8 (or up to 20 hours).
When you are ready to strain out the beans, line a pitcher with your nut milk bag. Pour the mixture into the bag, then squeeze the bag to get out all of the liquid.
Store the coffee concentrate in a container with a tight fitting lid in the fridge for up to 2 weeks. When you are ready to serve, dilute the concentrate with a 1:1 ratio of water or creamer of choice.