Achyut Adhikari, Kharel, Karuna, Fontenot, Kathryn
Washing fresh produce with potable water treated with a sanitizing agent can reduce microorganisms and pathogens that may be on the surface of the produce. Washing techniques and quality of water may affect the safety of the produce. Sanitizers must be used to minimize cross-contamination if the produce is washed together in a dump tank.
Potential problems include post-harvest rot and decay microorganisms, such as spoilage bacteria and yeast, Botrytis, penicillium and mucor as well as foodborne pathogens, such as E.coli, Cyclospora, Listeria, and Salmonella.
Chlorine can be used in wash water for apples, nectarines, plums, cherries, grapes (or muscadines), leafy greens, peppers, tomatoes, peas, melons, cabbage, green onions, cucumbers, zucchini squash and root vegetables, like carrots, sweet potatoes and others.
Do not wash or disinfect berries, such as strawberries, blueberries, blackberries or raspberries. While peaches and pears can be washed and sanitized, care must be taken because these fruits easily bruise and the washing process can damage the fruit and increase the chances of post-harvest decay.
In small- to medium-scale farms, produce can be washed using the immersion type of triple-wash system with circulating or non-circulating water. In either case, sanitizer is essential to reduce the risk of cross-contamination between produce during washing.
The triple-wash system of produce includes successively washing the produce in three dump tanks containing sanitizing solutions. Briefly, the produce is dumped in the first wash tank to remove the excess soil and debris from produce and then transferred to the second dump tank for further cleaning and then to the third dump tank for the final wash. When produce is dumped in the first tank, it should be in contact with the sanitizing solution for at least one minute. Depending on the type of produce it should be dipped, re-dipped, agitated or any suitable procedure necessary to remove soil from produce. The first two dump tanks should have higher chlorine concentrations (depending on the crop type) because organic matter, like soil, coming off the produce depletes the free chlorine rapidly. For final rinsing, potable water is generally used; however, adding a small amount of chlorine (target 5-10 parts per million free chlorine) in the final, i.e., third wash tank, will prevent buildup and cross-contamination of pathogens to produce.
Step 1. Remove soil and other types of organic debris from the surface of the produce before treating the product. Soil and organic debris reduce the effectiveness of chlorine. Before treating the produce with chlorine, rinse with potable water.
Step 2. Measure the temperature of your wash water. Wash water should be cool but not cold. Chlorine is most effective when water temperatures are between 55 and 120 degrees Fahrenheit. The wash water should not be more than 10 degrees Fahrenheit cooler than produce. When washing tomatoes, peppers, melons or other produce with large stem scars, the water temperature should be at least 50 degrees Fahrenheit higher than interior temperature of the produce. If the water is colder than the produce, plant and human pathogens can be sucked into the fruit. Chlorine cannot kill pathogens that are inside the fruit. Holding produce with large stem scars for four to five hours before washing will allow the scars to heal and reduce the potential for pathogen intake.
Step 3. Measure and mix chlorine into potable water. The amount of chlorine you add to your water depends on the concentration you want to achieve, and the desired concentration is crop dependent. If you are using household chlorine bleach (5.25-6.25 percent hypochlorite), avoid the “splashless” or scented formulations. It is important to make sure that sanitizers to be used in wash water should be of food grade. Furthermore, sanitizers with EPA labels are encouraged for use. The following table provides the ranges of chlorine concentrations that should be used to disinfect different types of produce. A minimum contact time of one minute is recommended to ensure the pathogens are killed.
|Produce type||Free chlorine strength (ppm)|
|Cabbage, leafy greens||100-150|
|Peaches, nectarines, plums||75-150|
|Peas (pod type)||50-100|
|Potatoes (red or brown)||200-300|
Assuming a concentration of 5.25 percent hypochlorite in chlorine bleach, use the following volumes to achieve a concentration of 65-400 parts per million chlorine.
|Amount of chlorine bleach/gallon||Free chlorine strength (ppm)|
|1 teaspoon (5 mL)||65|
|1 tablespoon (15 mL)||200|
|1 fluid ounce (30 mL)||400|
Volume of bleach equals desired strength of free chlorine in wash water× volume of wash water over concentration of bleach. To note, 1% equals 100 ppm, 1 gallon equals 768 teaspoons.
Example: If we want to make a 100 ppm sanitizing solution in 1 gallon of wash water using Clorox bleach with a concentration of 5.25% hypochlorite, volume of bleach equals 100 over 10,000 percent times 1 gallon over 5.25%.
Volume of bleach equals 0.0019 gallon.
Volume of bleach equals 0.0019 times 768 teaspoons~ 1.5 teaspoons.
Root crops harvested from farm
Root crops being washed in a triple wash system with sanitizer
Other sanitizers for use on fresh produce: The common wash water sanitizer used is sodium/calcium hypochlorite, which is commonly known as Clorox Additional products are registered for fresh produce sanitation, including chlorine dioxide gas or activated solution, hydrogen peroxide or dioxide, hydrogen peroxide plus peroxyacetic acid or peroxyacetic acid. Always make sure to read the label of sanitizers to see its concentration and if it is food grade.
Additional information on the various types of Produce Safety Alliance-labeled sanitizers for produce is available at: https://producesafetyalliance.cornell.edu/sites/producesafetyalliance.cornell.edu/files/shared/documents/PSA-Labeled-Sanitizers-for-Produce.xlsx.
For more information on these sanitizers and instructions on how to use them for produce sanitation, consult the Southeastern U.S. Vegetable Crop Handbook (https://pubs.ext.vt.edu/AREC/AREC-66/AREC-66.html).
Funding for this publication was made possible, in part, by the Food and Drug Administration through PAR-16-137. The views expressed in written materials or publications and by speakers and moderators do not necessarily reflect the official policies of the Department of Health and Human Services; nor does any mention of trade names, commercial practices, or organization imply endorsement by the United States government.