Back Loss due to evaporation during the storage of wine or spirits. Evaporation is particularly significant when storing wine in barrels. In humid cellars, it may not exceed 1%, but can reach 9% per year in very dry, warm and well-ventilated cellars. The average evaporation rate is 4 to 5% for storage in barrels. However, it is negligible in impermeable vats. In this respect, vinification in wood is more expensive, as frequent topping up must be carried out at regular intervals.