Written collaboratively by Joan Hegerfeld-Baker (former SDSU Extension Food Safety Specialist) and Rhoda Burrows.
The harvesting of leafy greens to maintain quality and safety focuses on the key risk factors from the time harvest begins to selling at market. The food safety risk factors involve temperature, time, water, worker hygienic practices, and food contact surfaces. Growers need to address these factors when harvesting for their family as well as their market.
Water Safety
Standards
As always, the water used on the leafy greens must meet drinking water standards. Water should be used to maintain the quality and safety of produce, not be the source of contamination. The standards set by the South Dakota Department of Health (SD DOH) are consistent with federal standards set by the Environmental Protection Agency. If using a public water supply assume it has been tested and meets safe drinking water standards. If using a private water source, such as a well, periodic testing is required to demonstrate that water has met safe standards for drinking water. Well water should be tested at least twice a year, before growing season and just before harvest. Proposed federal standards would initially require testing every three months, with reduced frequency allowed if no coliform bacteria are found in 5 successive tests. To have private well water tested, contact one of the SDSU Extension Regional Centers for a test kit. Some county Extension offices also have water-testing kits for your convenience. Obtain the water for testing from the source that is closest to what is being used in the post harvest operation. Flooding can contribute to contaminated wells, so have well water tested if at risk from contamination by flood waters.
Save all test results as documentation that you are addressing the risk of contamination by water that is often associated food borne illness outbreaks related to leafy greens and other produce.
Spraying
To maintain quality, leafy greens may be sprayed with a light mist when harvesting to reduce the loss of water. This must be an approved water source (having no E. coli) and the method used for spraying must not introduce additional contaminants. If the water is from a container, be certain the container and spraying equipment have been clean and sanitized. When possible, harvest early in the morning as the produce will be both cooler and better hydrated.
Disinfecting
Growers may choose to use an antimicrobial agent such as a chlorine- or peroxide-type disinfectant in the water. The primary purpose of this is to keep the water from being a source of contamination. Water with an active disinfectant can decrease microbes on the surface of the product, however, the efficacy will depend on the concentration, wash time, temperature, and completeness of physical contact. The disinfectant must also be approved for the intended use and all label directions adhered to. It is very important the grower understand the chemistry of the disinfectant they may be using, as its effectiveness can be affected by the pH of the water as well as dirt or debris in the water. Growers using a disinfectant in the water should also test the concentration of the disinfectant, using indicator test-strips. The pH of the water may need to be tested as well. If using a water disinfectant, monitor routinely to maintain proper concentration levels.and document all use and tests.
Cooling and Washing
The temperature of the water is also critical to food safety. When greens and other crops are harvested they are warm, and the crop needs to be cooled quickly to maintain quality and safety. However, using water that is greater than 10F colder than the recently harvested produce can create a phenomenon of infiltration of water into the plant. This is concern if using dirty water that may be contaminated with pathogens (particularly if washing in a container that is used to wash and cool fruits and vegetables), or if the outside of the produce has been exposed to contaminated soil or other surfaces. Therefore, it is suggested to use several washings using water that starts out slightly cooler than the produce and progressively becomes colder.
One option for smaller-scale growers is to use a pass-thru system, where the greens are spread on clean mesh trays that allow quick drainage, and they are sprayed with fresh clean water rather than submerged in a water bath. It may be necessary to stir the greens several times so that all surfaces are cleaned.
Equipment and Storage Safety
Refrigeration
After cooling with water, place leafy greens in a refrigerator to maintain a temperature of 32 to 36 F. The refrigeration unit should be kept clean. Do not store leafy greens in a closed container with other fruits or vegetables that produce ethylene gas as they ripen, such as apples, tomatoes, bananas, mangoes, onions and pears. High humidity (90 to 95%) needs to be maintained to minimize wilting, but avoid direct contact with standing water, which can serve as a source of cross-contamination. Clean moist (not soggy) paper towels can provide sufficient moisture if coolers are not equipped with humidifiers.
Tools
Harvesting equipment should be inspected daily during use. Make certain all knives, scythes, harvesting containers, etc. are properly cleaned and sanitized before use. That means washing in hot soapy water, rinsing thoroughly and dipping in a bleach solution of 100 ppm (1 tablespoon of bleach per two gallons of water) for 10 seconds and air-dried. Or, use a dishwasher to adequately clean and sanitize. Larger containers must be cleaned with hot soapy water, thoroughly rinsed then sprayed with a sanitizing solution and air-dried. All containers and harvesting equipment must be stored in a manner that will not contaminate the equipment. Have a system in place to maintain and monitor harvesting equipment. Consider the equipment used in harvesting fruits and vegetables to meet the same sanitation standards to safely prepare food in the home or restaurant.
Containers
Containers used in harvesting leafy greens and other produce should be labeled clearly for their purpose. This will not only reduce the risk for contamination by pathogens but chemicals as well. If you have several people working on your farm, communicating the risk factors and how to address these through best practices will improve morale in your growing operation as well as establish a culture of food safety.
Clothing
Those harvesting the produce need to be certain they are not wearing clothing and shoes that contribute to cross contamination. For example, shoes and boots should be dedicated to working in the garden, not in areas where livestock are located. Workers need to always wash their hands before harvesting. Clothing should be clean. And if workers are sick, particularly with diarrhea and/or vomiting they should not be handling produce, or clean containers and utensils. The risks of contaminated food by workers with a foodborne illness is critical at every step of the food delivery system from growing, harvesting, marketing, and preparing and serving.
At the Market
At the market, use tongs or disposable gloves if bagging leafy greens for customers and avoid setups that allow customers’ hands to touch raw produce. Vendors also need to develop systems so they don’t directly touch produce after handling credit cards or money, which are often contaminated with potential pathogens.
When harvesting, continually survey your growing operation to make certain you are implementing good agricultural practices from the field to the market.
