Many components of the storage environment impact shrinkage, but the most critical is relative humidity (RH). Actively managing the RH within the storage building will enable the maximization of the tonnage and quality of potatoes delivered.
Weight loss, or shrinkage, can be minimized during the course of storage by achieving the most ideal storage environment conditions possible. Preserving the quality, and quantity, of stored potatoes means gaining the best possible return on a grower’s harvested crop. Of all the factors impacting storage shrinkage, relative humidity (RH) is paramount. RH is the amount of moisture in the air at a given temperature, relative to the maximum possible humidity at that same temperature.
Importance of RH Control
Researchers from the North Dakota State University found that weight loss increases with sprout growth, since sprout growth adds to the surface area of the tuber and the high permeability of the sprout wall to water vapor leads to greater water loss. It has been estimated that the surface area of sprouts equivalent to 1% of that of tuber could double the potential rate of evaporation (Burton 1955). The high weight loss observed at 90-95% RH between 35 and 42 days of storage could be attributed to higher sprout growth leading to greater weight loss.
Respiration is also an important factor when discussing weight-loss, but researchers believe that respiration only accounts for about one-tenth to one-half of the total weight loss, except when tubers were stored in 100% relative humidity. Under these conditions, research shows there is an actual net gain, apparently from the tubers absorbing moisture from the surrounding atmosphere. Near the time sprouting began to occur the total weight loss accelerated. Also, the respiration rate increased appreciably as sprouting occurred.
A high relative humidity reduces the vapor pressure difference between the potato surface and the unsaturated air, thus reducing vapor losses. Previous studies have indicated that moisture loss is not affected appreciably by higher air-flow rates so long as the air has a high moisture content.
