Postharvest water includes any water that contacts fresh produce at or after harvest. This includes water used for rinsing, washing, cooling, waxing, icing, or moving fruits and vegetables. Postharvest water use may be a necessary part of fruit and vegetable production, but it is also a potential source of contamination. Understanding the risks associated with postharvest water use and how to minimize them are important for produce safety.
The key things you need to do to ensure the safety of postharvest water are to:
- Start with water that is the equivalent of drinking water.
- Add a sanitizer to all postharvest water.
- Change bulk/batch tank water when dirty.
- Make sure water is at the appropriate temperature to avoid infiltration.
- Clean and sanitize tanks/bins daily, making sure to reduce or eliminate pooled water.
- Document all postharvest activities.
Start with water that is the equivalent of drinking water
Only use water that is the equivalent of drinking water (i.e., potable) to begin all postharvest activities. Water quality should be verified through testing. Water testing can be done by the farm or by the municipality or water supplier, but the water must be tested to know its quality. Contaminated water can contaminate produce, so starting with clean water is essential. If you are using a surface water source, you will need to treat the water and regularly test it to make sure the treatment process is working.
Add a sanitizer to all postharvest water
Postharvest water, even if it is potable at the start, may become contaminated by produce that contacts the water. Adding a sanitizer does not clean each individual piece of produce, but prevents cross contamination from the water to the produce and limits the build-up of pathogens in the water. It is critical to add a sanitizer to all batch/bulk water where many pieces of produce are submerged in the same water because the risk of cross contamination is highest at this step.
Single pass water is less of a risk, but it is recommended that sanitizer still be added to the water. If single pass water is used inside equipment, a sanitizer should be added to prevent the formation of biofilms and pathogen growth inside the equipment.
A number of chemical and non-chemical sanitizers are available such as chlorine, chlorine dioxide, peracetic acid, hydrogen peroxide, ozone, and UV light. The choice of water treatment depends on the application, the type of product, and what is allowed by your customer or certifying group.
Always consider worker and environmental safety when choosing sanitizers. Remember to follow label directions and use proper personal protection equipment (PPE) when handling and mixing sanitizers. Levels of chemicals should be routinely monitored to ensure there is an appropriate amount to effectively reduce risks. Furthermore, some sanitizers, such as chlorine, are most active at a specific pH, so you will need to monitor the sanitizer levels and the water pH. Seek out expert technical advice before investing in a sanitation system or if you have questions.
Change bulk/batch tank water when dirty
Anything added to the batch/bulk tank water can introduce contamination. Leaves, stems, dirt, and even harvest containers submerged in the water, can contaminate the water and reduce the effectiveness of sanitizers. To reduce food safety risks, bulk/batch water should be changed frequently or filtered. One way to monitor water quality is by measuring turbidity. This can be done through the use of a turbidity meter or by developing other water clarity standards based on measurable observations. Establishing water quality standards for your postharvest water will guide decisions about when to change water. Resources are provided at the end of this summary to help you decide what is right for your farm.
Make sure water is at the appropriate temperature to avoid infiltration
Some vegetables and fruits, especially tomatoes, apples, and cantaloupes, are susceptible to water infiltration when the pulp temperature of the fruit is warmer than the water into which it is submerged. If the produce is warmer than the water, it may create a vacuum inside the produce and cause water to be taken up into the fruit. If that water is contaminated, the produce can be contaminated both inside and outside. To reduce the risk of infiltration, keep batch/bulk water the same temperature or less than 10Â°F warmer than the pulp temperature and avoid deep tanks (deep submersion = higher pressure = higher infiltration rates).
Clean and sanitize tanks/bins/washers daily
Making sure tanks/bins/washers are clean will reduce the risks of cross contamination. When daily cleaning and sanitizing is not possible, such as complicated equipment that requires disassembling, another schedule should be established to reduce pathogen and dirt build-up inside the equipment. Develop a policy and SOP that includes step-by-step instructions for cleaning and sanitizing, including what needs to be cleaned, how often it is to be cleaned, and the process for cleaning it. Your cleaning SOP should be specific and identify what items, parts, drains, hoses, and other equipment need to be cleaned. Remember to include instructions on how to eliminate or reduce standing water in the tanks/bins/washers because standing water provides the opportunity for pathogens, such as Listeria monocytogenes, to become established and persist. After cleaning and sanitizing tanks/bins/washers, all drip trays should be drained and any pooled water in the equipment should be removed as best as possible.
Personal protective equipment (PPE) and other necessary equipment should be specified in the SOPs. Use of photographs, drawings, and color-coding schemes is encouraged to aid workers in understanding exactly what needs to be done. SOPs should also be written in the language of the workers who use them. More information about cleaning and sanitation practices is available in the Sanitation and Postharvest Handling Decision Tree.
Document all postharvest activities
Records should to be kept of all postharvest water management and sanitation activities. Document the amount of sanitizer used, monitoring steps, how often water is changed in flumes/tanks, pulp and water temperatures, when equipment is cleaned, and any other activities that are part of postharvest water management. All activities should be outlined in your written farm food safety plan. Detailed SOPs and log sheets should be developed to ensure activities are done properly and documented. Sample SOPs and log sheets are provided within this decision tree.
Suslow, T.V. 2012. Top FAQs about Produce Wash Water Management for Small Scale and Direct Market Farms. Presentation at Center for Produce Safety Annual Meeting 2013.