Ceres Chill has an amazingly engineered, patent-pending dual chamber system. The outer chamber holds the ice - just a few cubes and a bit of water in contact with the inner Milk Chamber is all you need. You then just pump directly into the 12 ounce INNER Milk Chamber as needed throughout the day. Thermodynamic tests show milk being chilled down to 5°C within 1-3 hours and staying well within safe storage temps for 20+ hours in 20-25°C room temperatures.