PROPER ENVIRONMENT FOR POTATO STORAGE

1 The University of California Vegetable Research and Information Center PROPER ENVIRONMENT FOR. POTATO STORAGE . The authors are: R. E. Voss, Extension Vegetable Specialist, Davis; K. G. Baghott, Farm Advisor, Modoc-Siskiyou Counties; and H. Timm, Specialist, Department, of Vegetable Crops, Davis. The two critical environmental factors suberin layer (similar to a scab on animals). involved in properly storing potatoes are develops in 3 to 5 days. Cell regeneration, or temperature and humidity. Adequate and complete wound healing, can take place unrestricted air movement is also necessary beneath this suberin within 10 to 20 days, to maintain constant temperature and depending on the condition of the potatoes.

2 Humidity throughout the STORAGE pile, and to prevent excessive shrinkage from moisture When potatoes are placed in STORAGE , rapid loss and decay. cooling can result in more rot forming organisms in the tuber because the entry TEMPERATURE points remain unhealed. Rapid cooling, particularly in the absence of adequate air, Several factors can influence temperature can also result in black spot and other POTATO management for stored potatoes. These damage. include: whether the potatoes are to be marketed for processing, as fresh table Disease Growth and Infection stock, or as seed; the temperature of the tubers at the time they are placed in STORAGE ; Most disease organisms logarithmically the length of time the tubers are to be stored; increase their population growth at the extent of tuber damage at harvest; and temperatures ranging from 40 to 80 F.

3 The presence of disease organisms. Lower temperatures lessen the possibility of disease incidence during STORAGE . The STORAGE temperature affects the curing and wound healing processes, disease spread Since many of the common STORAGE diseases and severity, the sugar-starch relationships, naturally occur in the soil, they are and respiration. Respiration, in turn, transported into STORAGE with the tubers. It is influences dormancy or sprouting, and essential, therefore, not only to heal the weight loss. exposed wound areas to minimize pathogen penetration, but also to lower the Wound Healing and Curing temperature as soon as possible after storing to minimize disease spread within infected Tubers are often bruised and cut during tubers as well as from infected to sound harvesting and pre- STORAGE handling.

4 Tubers. Regardless of how the stored potatoes are to This fact emphasizes the importance of be marketed, wound healing is essential to careful harvesting and handling techniques minimize the entry areas for ever present to minimize bruising, skinning, and cutting. disease organisms. Healing proceeds most If late blight, other diseases, or field frost rapidly at temperatures of 60 to 65 F. At damage are evident in tubers, rapid lowering this temperature and with a high humidity, a of temperatures , even without the healing Page 1. The University of California Vegetable Research and Information Center and curing period, may be necessary to optimum wound healing during the curing prevent breakdown.

5 However, do not store period. It is also essential during the entire these damaged potatoes for long periods of STORAGE period to minimize tuber weight time. loss; weight loss rapidly increases at relative humidity levels below 90 percent. Respiration and Sprouting AIR MOVEMENT. The POTATO tuber reacts like any living organism; respiration increases with Air movement may not be necessary during increasing temperatures . When the the curing period because the heat and respiration increases so does the tuber moisture generated by the potatoes may weight loss. Since lower temperatures also provide an ENVIRONMENT that is favorable for maintain dormancy, keep temperatures as wound healing.

6 Low as possible without otherwise decreasing quality ( , sugar buildup in Do not allow free moisture (condensation) to processing potatoes). For long STORAGE form during STORAGE . If that does occur, air periods of 3 to 5 months, depending on the circulation may be necessary. Thereafter, air variety, a sprout inhibitor is practical for movement may be required to maintain the potatoes other than those to be used for seed. desired temperature and humidity throughout the STORAGE pile. This may also Sugar-Starch Conversions require passing humidified air and/or heated or refrigerated air through the pile. Low temperatures (45 F.)

7 Or lower) enhance sugar formation. If the STORAGE temperature From 10 to 20 cfm (cubic feet per minute) of is maintained below 45 F. for a long time, air per ton of potatoes is usually optimum, accumulated sugars in the tuber do not but the exact amount depends on the readily reconvert to starch (recondition). temperature of the outside air being brought High-reducing sugar concentrations result in in--warmer temperatures make more air undesirably darkened POTATO chips and fries. necessary. The primary function of air Some varieties recondition better from low movement is to maintain a uniform temperatures than others.

8 Norchip, for temperature and humidity. Therefore, example, reconditions better from 45 F. continuous air movement is not necessary STORAGE temperatures than does Kennebec. since intermittent air movement can accomplish this goal. In general, the optimum, long-term STORAGE temperature for processing potatoes is Dirt and clods are a problem that can approximately 45 F. For fresh market seriously affect air movement through the potatoes, a temperature of 40 F. is STORAGE pile. They tend to form a solid recommended. Seed potatoes may be stored barrier that slows down air movement and at slightly lower temperatures (38 to 40 F.)

9 Prevents air from reaching some areas of the for better weight loss and sprout control. pile. HUMIDITY REMOVAL PERIOD. Maintain a 95 percent relative humidity at Cold potatoes are brittle and may easily all times. High humidity is essential for bruise or shatter during handling. Before Page 2. The University of California Vegetable Research and Information Center removing the tubers from STORAGE , raise the Wound healing occurs most rapidly temperature to 50 to 55 F. This can at 60 to 65 F., with 95 percent sometimes be accomplished by removing humidity, and requires from 5 to 20. ventilation, which allows the heat from tuber days.

10 Respiration to accumulate. More frequently, however, heaters and/or forced ventilation of If blight, other diseases, or frost warm air is necessary. damage is already present, it may be necessary to minimize or bypass the SUMMARY curing period. Minimize bruising, skinning, and The holding period requires low cutting during harvesting and temperatures of 45 F., 40 F., or 38 . pre- STORAGE by very gently F. for processing, fresh market, or performing the entire operation. seed potatoes, respectively. Maintain 95 percent relative humidity. Remove clods and dirt before putting the potatoes into STORAGE . Removal period: raise temperature to 50 to, 55 F.