VIDALIA ONION RESEARCH LABORATORY
UNIVERSITY OF GEORGIA
TIFTON CAMPUS
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VIDALIA ONION RESEARCH LABORATORY UNIVERSITY OF GEORGIA TIFTON CAMPUS
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MAINTENANCE AND CLEANUP OF VIDALIA ONION HANDLING AND STORAGE FACILITIES (ESPECIALLY CA STOREROOMS) Now is a good time to check out handling and storage equipment and facilities before they are needed for the upcoming onion harvesting season. The checklist below can assist you in making sure that your storage rooms operate satisfactory this year. 1. Rotted onions from last season and the dried juice from rotted onions are a prime source of inoculum for infecting freshly harvested onions during grading and packing before and during storage. A thorough cleaning of all work areas, storage rooms, pallet bins and grading and packing equipment, including rollers and belts, should be done well in advance of anticipated use. However, remember that many cleaning and sanitizing agents are strong oxidants and are corrosive to refrigeration and other equipment unless it is properly protected. Cleaning equipment and storage rooms will go a long way in reducing rots in storage. 2. If you had rooms that required excessive nitrogen and/or carbon dioxide additions during operation last year, you may want to run a pressure test to find out if they are leaky. The most accurate pressure tests are made when weather conditions, temperature, barometric pressure, and wind are all stable. The room should be empty and at ambient temperature with all refrigeration, lights and fans turned off when the pressure test is made. To pressure test a room, seal all openings (doors, portholes, vents, pressure relief ports, electrical boxes, etc.) and pressurize the room to a known pressure level (i.e., 1.0" of water or 0.8" water on the pressure magnehelic gauge) with an air fan, blower or vacuum cleaner. Monitor the pressure loss with time until half of the original pressure remains. Plot the pressure with time on a Pressure Test Data Sheet (attached). Air-tight rooms should hold one-half pressure for at least 30 minutes. Leaky rooms yield a steep sloping line (i.e., the 20 minute line); tight rooms lose pressure at a more gradual rate. If a room cannot be made air-tight it will be difficult to establish CA and you should consider to use the room only as a cold room.
3. Breather bags are designed to reduce the small pressure imbalances resulting during the normal refrigeration on/off cycle, defrosting of refrigeration coils, barometric pressure changes in the atmosphere and pressure changes caused by high winds when the CA rooms are in operation. Check breather bags to ensure that there are no holes in them or leaks around their connections to the room. 4. The pressure-vacuum relief ports are calibrated to relieve pressure and vacuum changes greater than those accommodated by the breather bags. Check the pressure-vacuum relief ports to ensure that the rubber diaphragms are pliable and are not torn. Replace torn or brittle diaphragms. Malfunctioning pressure-vacuum relief ports can result in leaky rooms or the development of excessive positive and negative pressures (greater than 0.25" of water on the magnehelic guage) which can cause structural damage to the room and gas seal. 5. Each store room should have at least two evaporator units with the defrost cycles of the evaporators staggered to reduce air volume changes and the amount of water added to the atmosphere. Perform (or have performed) routine maintenance on all components of the refrigeration system, such as cleaning the condenser coils and fans and evaporator fans and blowers, replacing worn belts and lubricating bearings, and checking oil levels and refrigerant levels. The thermostat should also be checked to ensure that it is controlling temperature within the desired limits. 6. Forced air circulation is absolutely essential to keep the temperature, relative humidity and atmosphere uniform throughout the CA room. Check the capacity and condition of the air circulating fans. Circulation of the storage room air should be forced at 100-200 cfm/ton of onions. Undersized fans will not adequately circulate the air in a room filled with produce. The fans should be at the end of the room opposite the door, so that air is drawn through the bin openings into a plenum area and then blown over the cooling and dehumidification units attached through the roof of the CA room. Good air circulation around onions in bins will eliminate pockets of elevated temperatures and humidities which promote decay. 7. Accurate recording of temperature is important since some Vidalia onions can freeze at about 30.8 EF. Thermometers and remote temperature probes can be calibrated by placing them in a stirred 32 EF ice water bath. Mark the correction factor on every probe and thermometer with a tag or tape with the statement, "Add (or subtract) 00 degrees to reading." 8. It is absolutely essential that relative humidity in store rooms be maintained at 70-75% to eliminate or reduce rots. However, at this relative humidity, 10,000 bushels of onions will lose 7-10 pounds of water per hour and the dehumidification system must be capable of removing this amount of water without significantly affecting temperature. Humidity sensors should be calibrated at least annually. If you do not have a calibrator, remove the sensor and send it to the manufacturer or supplier. Calibrating humidity sensors is not as simple as calibrating thermometers and temperature probes. 9. If nitrogen is being generated on-site with a membrane, the filters that trap particulates and oil from the air before it goes through the membrane should be replaced annually. No other maintenance is required for the membrane itself. However, routine maintenance on the air compressor, such as changing the oil and filters, should be done.
If you have questions please contact: Dr. Albert C. Purvis Horticulture Department Coastal Plain Experiment Station Tifton, GA 31793-0748 Tel. 912-386-3900 |
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Send mail to paulk@tifton.uga.edu with
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