Weight loss can reduce profits by reducing the quantity and quality of marketable potatoes. It is often simply tolerated, but minimizing weight loss should be a top priority in the storage process. Many components of the storage environment affect shrinkage, but the most important is relative humidity. Active management of the relative humidity in the storage facility will maximize the tonnage and quality of the potatoes delivered to the end customer.
Effect of Relative Humidity on Shrinkage
Stored potatoes lose weight by transpiration and during respiration. Weight loss through respiration is much less than through transpiration water loss – it cannot be completely stopped, but can be slowed down by keeping the relative humidity as high as possible.
Current recommendations are to maintain a relative humidity of at least 90%, and preferably more than 95%, throughout the storage period. This only works if the crop is healthy, with low levels of disease presence.
Air ventilation with high relative humidity is especially important immediately after harvest and during drying. For example, studies show that when storing Shepody potatoes under warm conditions (average pulp temperature of 25°C) almost half of the total shrinkage occurred during the first week after harvest. The higher the relative humidity during storage, the less water is lost per unit time.
Humidification in storage
Different types of equipment can be used to achieve the desired relative humidity in a storage facility: cooling panels, evaporators and high-pressure nozzles. Regardless of which equipment is used, it is very important to check that it is in working order before putting in the crop. Clogged cell material or worn-out turntables can severely limit the ability to supply enough water to maintain the desired relative humidity. In addition, relative humidity sensors should be checked annually and calibrated or replaced.
Monitoring the relative humidity of the storage chamber and actively working to achieve the highest possible relative humidity without excessive condensation should be the primary goal. It is clear from the example scenarios described that maintaining the desired relative humidity is critical to maximizing income from the stored crop.