Web site - Guidelines for Fruit Storage

Guidelines for Placing Fruit in Storage

First, segregate fruit into lots by storage potential. The following types of fruit should not be stored for more than 5 months because of their potential to break down or develop bitter pit:

Large fruit from lightly cropped trees
Fruit from excessively vigorous trees
Fruit from young trees just coming into bearing
Fruit from interior portions of trees that are heavily shaded
Early picked fruit high in starch
Fruit with a low number of seeds (less than five per fruit)

Second, cool the fruit as rapidly as possible after harvest. Just as workers are at risk from high heat, so too are fruit. Removing bins from direct sunlight under high-temperature conditions is a priority. Exposure to elevated temperature reduces the storage and shelf life of the fruit. The sooner you are able to get fruit into the warehouse and under refrigerated conditions, the better. Balancing the capacity of your refrigeration system to the heat load and volume of your freshly harvested fruit is important. Do not overtax the cooling capacity of your system to the detriment of fruit already in storage. If you plan to use controlled-atmosphere (CA) storage, in general the more quickly you cool the fruit and achieve the desired atmosphere, the longer the fruit will store. For best results in CA storage, cool the fruit for 2 to 3 days, then achieve the desired atmosphere within 7 days or fewer after harvest. Since most CA rooms are not filled in 1 or 2 days, CA pulldown can commence shortly after the room is filled during the cooling process. Achieving the target temperature for storage should precede achieving final CA conditions. Some newer varieties, such as Braeburn and Fuji, need to be cooled thoroughly (40 degrees F for 14 days) prior to applying CA conditions. Typically these varieties are quite dense and do not respond well to elevated levels of carbon dioxide (internal or external).

Third, when placing fruit in storage, leave representative samples of each cultivar and orchard block close to the door, and check the samples periodically to determine fruit quality. Do not "bury" fruit deep in the storage room with no way to check its condition.

Fourth, maintain a high relative humidity in the storage room. Apples are approximately 85 percent water and can quickly lose enough moisture to show signs of skin shrivel if kept at too low a humidity. Shrivel can appear after an apple loses as little as 3 percent of its fresh weight. Abrasions, bruises, and other injuries increase the rate of water loss. A single bruise can increase water loss nearly fourfold. Warm fruit is cooled by giving up moisture. As moisture is removed from the air by the cold refrigeration coils, a deficit gradient is produced that pulls more moisture out of the fruit, which can result in shrivel. Once the fruit has been cooled, the refrigeration coil temperature can be raised to reduce the amount of moisture being removed from the air.

In general, a relative humidity of 90 to 93 percent gives the best results for storing most apple cultivars and is recommended when mixed cultivars are placed in a common storage. Relative humidity is the amount of water that is present in vapor form. The amount of water needed to raise the humidity is actually very little because of the inability of cold air to hold moisture. Free water on the floor of a refrigerated or CA room does little to increase the relative humidity of the room. Fogging systems have been employed to increase the relative humidity in cold rooms. Fogging systems work better than water on the floor because fog is composed of very small droplets whose combined surface area can be a thousand times greater than that available from the area of the floor alone.

SmartFresh (1-MCP)
SmartFresh, 1-methylcyclopropene (1-MCP), is being registered and marketed by AgroFresh, a Rohm and Haas company. 1-MCP will bring dramatic benefits to the fruit industry. The mode of action of 1-MCP involves inhibiting the ripening process by attaching the ethylene-binding sites and rendering the fruit insensitive to ethylene exposure. This binding results in fruit that maintain firmness and acidity levels higher than those of untreated fruit. For treatment purposes, 1-MCP is a gas and must be applied in an airtight room or chamber. 1-MCP has been shown to be very active at low concentrations. Its label rate for application will be 1 ppm for a period of 24 hours. Other benefits include inhibition of superficial scald in varieties that are prone to scald occurrence, such as Red Delicious and Granny Smith. Applications of 1-MCP should be made on fruit that is designated for intermediate to long-term storage. Recent work at Cornell indicates that the use of SmartFresh on cultivars that have high levels of volatiles, such as McIntosh and Gala, may have some undesirable effects. 1-MCP will suppress the natural evolution of volatiles that consumers have come to expect. Cultivars that have low levels of natural ethylene during harvest respond best to SmartFresh. However, cultivars that have high levels of ethylene production during harvest do not respond as well. Natural ethylene levels can be stimulated by warmer temperatures or by delaying harvest in an attempt to obtain better color. Blocks treated with ethephon to hasten maturity also do not respond well to SmartFresh treatment. Delaying treatment of fruit for more than 7 days may result in less-than-optimal performance. Fruit should be treated within 3 to 4 days after being placed in cold storage.