Postharvest Handling and Storage of Blackberries and Raspberies
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First published in the Southern Region Small Fruit Consortium’s “Small Fruit News” newsletter (April 2010), revised 3/25/2013.
Of all the small fruits, raspberries have the shortest shelf life. One can watch the mold grow on raspberries held on the counter at room temperature. In addition to decay, raspberries often change from a bright red color to an unattractive purple color, signaling overripe fruit to many people. Blackberries are somewhat easier, being less prone to rapid mold. While blackberries won’t get unacceptably dark, they can develop color reversion, either in patches of drupelets or all over the fruit depending on the reasons. Both raspberries and blackberries become very soft in a matter of hours if not held at cold temperatures.
To further complicate matters, neither raspberry nor blackberry can be picked half ripe, as they have no carbohydrate resources within the fruit and depend on direct import of sugars from the plant to facilitate full size, sweetness, texture and color. Raspberries can be picked at the light pink stage and will attain normal sweetness and color, but blackberries must have full black color. The fruit don’t like being picked wet with dew or rain, nor can they be cleaned or cooled using water. The high respiration rate of the fruit, combined with the ability to quickly lose water and weight from the lack of a protective peel or rind, mean that the fruit must also be rapidly cooled and kept cold during the handling and marketing process. Raspberries and blackberries are harvested by machine for processing, but are too soft for machine harvesting for fresh market. For these reasons, fresh market fruit are picked by hand in the field and placed into final containers.
As with many fruits and vegetables, the first answer to longevity is careful choice of cultivar and variety and decisions made about the type of system. Will fruit be used for processing or fresh market? Processed fruit must be of varieties that don’t have high drip loss, maintain black color after freezing and can be picked fully ripe. Blackberries in this category include Marionberry, Obsidian, Metolius; raspberries include Meeker. Fresh market fruit usually are not of the same varieties as processed fruit. Fresh market fruit must detach at a slightly less ripe stage (shiny black rather than dull black or light red, rather than dark red for raspberries) and be very firm, especially if shipping long distances. Blackberries suitable for shipping include Chester Thornless, Apache, Ouachita, Navaho, Osage, and Natchez. Raspberries include Nantahala, Nova, Autumn Bliss, Autumn Britten, Heritage and Himbo Top. Fruit for local or on-farm markets can be of softer types, and often with raspberries it’s better to have more flavorful types, such as Caroline, or large fruited blackberries such as Kiowa (thorny) or Apache (thornless).
Caneberries have to be selected first for productivity and disease resistance in the environment where it will be grown, and second, but just as important, for fruit quality in that environment. For instance raspberry varieties developed for the Pacific Northwest have poor vigor in North Carolina. Blackberries are somewhat easier to adapt to the South because there were many varieties released from a southern breeding program in Arkansas, or from a federal breeding program in Maryland, so they tend to be more heat adapted.
Production practices, such as the amount of nitrogen, rainfall or irrigation, can also affect fruit quality. Drought and heat can greatly reduce raspberry fruit size, while irrigation within 8 hours of picking can soften blackberries; water droplets standing on the surface of blackberries can cause a reddening effect. Food safety issues need to be considered both with choice of fertilizer and with irrigation source in order to reduce food contamination risks. Above all, avoid putting soft, decayed or injured berries into the packs. These fruit will accelerate decay of the whole pack.
As mentioned earlier, fruit are harvested into their final container in the field. Essentially there are only two handling steps: the initial harvest and final consumer use. Fruit are usually taken to an in-field grading shed mounted on a trailer so injured or overripe fruit can be removed. The packs are then placed directly into a refrigerated truck and taken to a distribution/collection point, cooled with forced air and held in cold rooms until loaded for shipment to the buyer’s designated point. Selection of container should center on the type of cooling and effectiveness of the package in allowing air flow. Other factors such as ability of the packs to be stacked, the smoothness of the holes (to avoid fruit injury) and size should be considered when choosing containers. The market sometimes dictates what container size will be harvested for that period, but initial choice of materials and style should be made carefully.
Cooling can be done by room cooling if pallets of fruit are stacked with aisles between them and the size of the room is adequate for the room to get efficient cooling. Generally, cooling of large amounts of fruit is not efficient unless cool air is forced into and around pallets. This can be done using a tarp and box fan or by building a cold wall at one end of the cooler that has outlets to line up fruit. Cooling is especially critical for raspberries, which can mold in as little as a day if held at 68 degrees F. For each hour in delayed cooling, a day of shelf life is lost. Caneberries can tolerate elevated carbon dioxide (10 to 20 percent) and slightly reduced oxygen levels (10 to 15 percent), but some raspberries can have altered flavor after modified atmosphere (MA) storage. Generally, MA in caneberry is done just before shipment because the fruit must be delivered to consumers within five to 10 days of harvest.
Consider the following questions before planting blackberries:
- What is your market: local or national?
- What varieties will suit your market (large, softer, good flavor, size, firmness)?
- What type of packaging and size of package will you need?
- What type of system will you use for harvest?
- What type of cooling facility will you have?
- Will you be using modified atmosphere during storage and shipment?
- What are your food safety hazard points from production through shipment and sales?
Major issues that make caneberries different in handling:
- No protective cuticle.
- High respiration rate.
- High rate of weight loss.
- Have to be picked near full ripeness.
- High rate of softening.
- Susceptible to gray mold (Botrytis cinerea).
- Blackberries can turn red.
- Raspberries can turn purple.
- Maximum shelf life is short (two days to two weeks).