If you are brewing your own cold brew, you should do the following ratio: 7 oz of Ground Coffee *to* 28 oz of water = yields 16 ounces of coffee concentrate. Then, add 32 ounces of water to the concentrate, and you will have a perfect 48 ounces of cold brew in your 64 oz keg. (note: reduce to 40 oz to avoid gas escaping) Otherwise, you can simply purchase store bought cold brew (use 40 of the 48 oz of Starbucks or STOK flavors) and add it directly to the keg, nitrogenate, shake, and wait 1 hour. Happy pouring! (Note: Use 80 oz for 128 oz keg)