Introduction to Post-Harvest Food Handling

Savvy consumers have high expectations. They want their meat, produce and processed food products to be nice looking, nutritionally sound, good tasting and free from microbial risks. The small farmer can capitalize on these expectations by consistently delivering the best possible product. Most locations have direct consumers, stores and restaurants willing to pay for quality. But quality isn’t easy to achieve. Careful attention to detail is required from pre-planting decisions through final sale.

A post harvest marketing and management plan begins with decisions about product selection, farming techniques and marketing strategies. For example, if you are selling onions, do you plan to store them? What percentage and for how long? The answers to those questions, along with your knowledge of the market, will guide your variety selections. You wouldn’t grow exclusively “sweet Spanish” onions if you want to be selling onions in February. Other onion cultivars have much better storage characteristics.

Production practices influence the incidence of certain defects like green-skinned potatoes, garlic without outer “skins” and green shoulders on carrots. A successful farmer learns to recognize the most common defects and address their causes.

Someone selling lamb would need to know what their consumers/buyers want, i.e. whole small live lambs for celebrations, prime cuts like legs and chops, grass-fed only, etc. Those answers might well determine breed raised, time of lambing, feeding and management decisions, and processing options.

Production cycle pests (insects and diseases), nutritional deficiencies and human pathogen contamination can have a major impact on crop quality and storage life. A good plan to manage those problems will make the harvest more productive, leading to less field cull and better post-harvest quality. The amount of produce that is culled before packing and sale represents a significant financial loss due to wasted production input costs and wasted harvest, handling, culling and disposal costs. Grower post-harvest objectives are fairly succinct:

  • Maintain the quality of the harvested product through sale and consumption
  • Prevent harmful microbial contamination

Post-harvest issues may include

  • Quality of the product at harvest
  • Damage during harvest
  • Post-harvest labor requirements and management
  • Need for cooling and/or further processing
  • Need to ripen the crop after harvest (e.g. winter pears)
  • Time between harvest and sale
  • Storage risks
  • Relative costs of post-harvest technologies
  • New technologies
  • Regulatory issues (meat and other processed products)
  • Liability concerns

Microbiological contamination has been much in the news recently. There are a number of human pathogens that can contaminate fresh produce. Most are introduced by contaminated irrigation water, fresh manure in production fields, or poor worker sanitation at harvest or post-harvest processing. Once introduced, these pathogens can be difficult to remove. References cited at the end of this article will help guide your thinking on this crucial subject. Prevention strategies need to be implemented in every operation. These are often called “good agricultural practices” (GAP) plans. See the references for more information on GAP.

Specialty growers are often selling unique varieties that don’t ship well. The reason such crops don’t ship is that they are tender and must be handled with great care all through the harvest and sale process. Harvest equipment may have to be modified to reduce bruising. Special bins or crates may be needed. Farm labor must be trained to handle tender crops. Compensation rates for picking tender crops must account for the care required.

In general, most vegetables and fruits are chilled after harvest to lower their respiration rates. This helps to maintain eating and nutritional quality and lower decay loss. Humidity in storage can be manipulated to maintain a fresh appearance. Berries, which are often quite fragile, are best picked early in the day to minimize their “field heat”. There are a lot of techniques to remove field heat from fruits and vegetables. Certain vegetables are commonly chilled by “icing”, others by quick transport to a properly sized refrigeration unit and some are “hydro-cooled”.

However, sub-tropical vegetables or fruit (including tomatoes) are easily damaged by temperatures under 50-55 degrees F. This is called chilling injury. It is important to know the temperature and humidity requirements for the crops you grow.

Fruit is generally harvested at the right balance of sugars and acids and the proper eating texture. Further ripening is not desirable. However, winter pears require cold storage before they can go through the ripening process. Other fruit may benefit from some controlled ripening as well.

Ripening is a complex process where starches are converted to sugars and the fruit starts to soften. There is a naturally produced plant growth regulator called ethylene that is central to the process. As fruits ripen, they give off increasing amounts of ethylene. This stimulates ripening of surrounding fruits. Decaying fruit will produce increased amounts of ethylene (“a rotten apple will spoil the bunch”) which also stimulates ripening. Stored winter fruit is held at or near 32 degrees F to slow respiration and the ripening process. Controlled atmosphere storages (impractical for the small farmer) chill the fruit, lower the atmospheric oxygen content to further slow respiration and may also “scrub” ethylene from the storage facility. Ethylene can also cause potatoes to sprout and carrots to turn bitter. If you are storing fruit, some segregation from other produce within refrigerated facility may be needed.

A diverse produce mix and varying storage times can complicate the management of your facilities. Get to know the best techniques to handle your produce mix and how to work around the sometimes competing requirements of different produce items.

The decision to store and market produce over a longer time frame has risks, challenges and rewards. The risks are primarily from loss of product quality in storage and selling prices that are not as good as you budgeted. With the movement of food from great distances, summer apples in New Zealand or other Southern Hemisphere locations compete with stored U.S. apples from the previous fall. Grower challenges often involve smaller deliveries to a number of sites. The expense of maintaining refrigerated storage is also an increasing problem. Most grocers won’t hold much inventory so they make you store and deliver the product. The rewards come from selling your produce at a premium when other local produce is unavailable. The premium has to be large enough to cover the increased costs, storage loss and the like.

There are excellent resources to guide you in the design of facilities and equipment appropriately sized for your operation. If you are certified organic, your certifying agent may have specific suggestions for you that go beyond or interpret the national organic standard as it relates to post-harvest concerns. Of particular importance are rules on pre-plant manure applications and the use of specific disinfectants in the packing line.

Food technologists in universities and private industry have created a lot of innovations in fresh packaging tools and techniques including a variety of permeable films, new container styles, and many other products. Some of this technology is adaptable to small farmers.

Further processing of fruits or vegetables into storable products like jams, pickles, frozen packages and other items requires substantially more investments in equipment and after-harvest labor. Specialty product processing is regulated by the Food and Drug Administration on a federal level and by the Oregon Department of Agriculture’s Food Safety Division in Oregon. Your ODA contact can be of great help in discussing your ideas and getting information about safe commercial food processing.

This has been a very brief introduction to post-harvest handling. For more information, check out these resources:

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