Overrun refers to the amount of air that is added to the ice cream during churning. An ice cream with 50% overrun means that for every 2 litres of ice cream, you will have 1 litre of air added. At 100% overrun, you’ll get equal parts ice cream and air. Commercial ice cream machines have powerful dashers that can add 100% overrun or more. Most at home ice cream makers don’t have the same power and create significantly less overrun.