Prep. Grind the beans to a coarse size grind. The grounds should resemble kosher salt.
Brew. Combine the coffee grounds and cold filtered water in a large container. Let sit for 12 to 16 hours. Strain through a paper filter or a fine-mesh cheesecloth (see notes). Because nitro coffee is brewed to be ready to use it is a slightly different ratio than traditional cold brew coffee, it does not need to be diluted.
Bubble. In a soda dispenser - or a whipped cream canister - add the cold brew coffee. Seal and add the nitrogen cartridge. Give the cannister a shake. Turn it upside down and release it into a glass with the dispenser tip at the bottom of the glass. Let the coffee settle and the creamy foam head form before sipping.
You can experiment with flavors by adding vanilla or other extracts to the coffee before sealing the dispenser.
If you're in a rush, you can substitute cold brew concentrate and use slightly less water when you dilute it. I typically prefer the ratio of 2 parts concentrate, 1 part water for my cold brew concentrate.
If you need to speed up the brewing process you can substitute hot water for cold water, then brew for 6 to 8 hours but this make extract some acidity from the beans.
I love these reusable cloth cheesecloths (affiliate link). If you plan to make a lot of cold brew, they're 100% worth the small cost.