By: Anna Brunner
The Purpose of This Document: To describe the general protocols involved in safe
post-harvest food handling during the washing, grading, and packing processes.
Goals of Post-Harvest Processes
There are three main goals to keep in mind during the post-harvest process:
1) Minimize contamination of produce,
2) Protect the produce from unnecessary damage from handling, and
3) Maximize the amount of produce that successfully makes it to market.
In order to accomplish these goals it is important to have a clear understanding of the harvest and post harvest process. This clarity can help shed light on areas in your process chain that may need improvement or modification.
Wash Pack Area Preparation
Organize your wash pack area so that it maximizes efficiency. If you place your washing station materials and machinery in the order your process food in, you will minimize time wasted moving from one area of the room to another. Because the wash pack needs to be easy to sanitize and keep sanitized, the surfaces in the wash pack should be chosen with this in mind. Similarly, the floor of the wash pack should be fairly easy to clean with a drain to prevent standing water. Finally, the lighting in the wash pack must be slightly specialized: there must be enough light to clearly illuminate the work area so that workers can easily spot undesirable produce and the light fixture must be shatter proof so that glass or other materials in the lights does not contaminate the produce [Source 1].
All water used in the wash pack must be potable. This requirement includes water that is used to clean and sanitize surfaces. If any ice is used in the packing process, it must have been made with potable water as well. Another way to minimize contamination of produce is to minimize the number of workers involved in the harvesting, washing, and packing processes. The more people who contact the food, the more bacteria from various sources have a chance to contaminate produce. All workers who process food should be trained in the farm’s harvesting, washing, and packing protocol. Because part of these rules require workers to wash their hands and then refrain from touching their face or hair, and children may have more difficulty following this important rule, they should not be allowed to harvest, wash, or package food. Similarly, all animals, wild or domestic, should be kept out of the wash pack area to prevent the spread of germs. Therefore, it is important to have well-sealed doors from the wash pack to the building exterior and to the storage site [Source 1] [Source 2].
Know the order you will use to process produce beforehand, as this will allow you to prepare the wash pack. For example, if you need ice to store the produce, have that ready to go prior to harvest. You will also need to clean and sanitize the surfaces of the wash pack prior to processing. Just prior to harvest, be sure to sanitize your harvest containers. Plastic containers with lids are best, since plastic can be easily cleaned and the lid maintains cleanliness for a longer time. If possible, keep the harvest container off of the ground and the lid sanitary during the harvest process. Sanitize any harvest tools you may be using between produce types. Always wash your hands prior to harvest, as well, regardless of whether or not you will be using a tool [Source 1].
During Harvest and Immediately Post-Harvest
While you are harvesting, it may make sense to sort the produce into rough grade categories and/or sizes. Produce that cannot be sold at market due to appearance or spoilage should not waste your time being washed. Additionally, washing spoiled produce can introduce contamination into the water. If you sell seconds at a farmers market or to another retailer, separating the product in the field can also save time later on when, depending on how your wash pack is set up, it may be more difficult to reliably sort each piece of produce. Sizing—another type of sorting—can also be done in the field, but may lend itself better to sorting during the packaging process. In the packaging section, the reasons for sorting by size will be discussed. If you want to know more about the official grading process used by the USDA, it can be found here [Source 3].
Most produce will last longer if it is cooled as soon as possible after harvest. Some farmers may want to put chilled, potable water in a bucket in the field to submerge the produce immediately. This can help prevent wilting by greens. Regardless of whether or not you choose to cool your produce in the field, it is important to minimize the time in between harvest and washing and packing. During this time produce can wilt and is more susceptible to germs. Having a sanitized lid to cover your harvest can help minimize any additional contamination between the field and the wash pack [Source 4].
In the Wash Pack
If you use any chemicals to help clean the produce, check their concentration and pH beforehand. Additionally, confirm the water temperature is appropriate. Follow the washing procedure your farm has laid out for various produce. If there are multiple steps, make sure each area used preserves the cleanliness achieved in earlier stages. If dirt and bacteria are washed off during one step, but the latter step is not sanitary, the process will not achieve the desired results. Similarly, it is important to wash your hands once the harvest produce has been delivered to the washer to maintain cleanliness [Source 1].
Package the produce using containers that are clean, and have been stored at least six inches off of the ground in a protected way, such as a bag or lidded box. Then put packaged produce into a clean holding area with proper temperature/moisture conditions before transport to vendors/customers. Most fruits and vegetables have a proper holding temperature between 32-38 degrees Fahrenheit, although this does not hold for tropical produce. Above 40 degrees Fahrenheit, bacteria begins to accumulate more rapidly on food surfaces, and so keeping produce cool not only prevents bacteria growth, but also prevents over ripening or wilting. However, keeping produce too cold can also damage the food. Source 4 contains a list of some common produce and the minimum safe temperature, along with a description of the way damage manifests itself, on page 122 [Source 4].
The packaging for food will likely change depending on the type of produce. Ideally, packaging will be sturdy enough to protect the food as it travels to market. Do not pack containers too full as the produce can get squashed and injured; conversely, packing containers too light will waste space and can cause produce to bounce around and bruise. For fruits that release ethylene (a ripening gas) be sure to provide plenty of ventilation.
There are many types of packaging available, and choosing the best one for your produce, budget, and storage facility will be an important part of making your operation feasible. Regardless of your choice, the packaging should be marked as food-grade. Source 4 lists some things to consider when choosing packaging for produce on page 65. On page 133 of the same source, there is a useful list giving the length of time various produce can be held for without spoilage, if kept at proper temperature/moisture conditions [Source 4].
Maintaining the Wash Pack
Make sure to thoroughly clean the wash pack daily, as a build up of dirty organic material can produce unsanitary conditions. Cleaning the area promptly will also help deter pests from entering the wash pack in search of food. For GAP certified farms [see GAP Certification Document], keeping track of various procedures in the wash pack is mandatory. For other farms, it is a good way of getting into the habit of following farm cleaning protocol and can help defend the farm against any allegations of food borne illness. GAP requires you keep track of [Source 1] [Source 2]:
-location of harvested food (relative to farm map)
-individual who harvested the produce
-day of harvest
-date of last wash/pack sanitation (initials of person overseeing project)
-concentration of cleaner used in sanitation (initials of person overseeing project and date)
-concentration of produce cleaner, if any is used (initials of person overseeing project and date)
-temperature of holding area for packaged goods (initials of person overseeing project and date)
If produce such as garlic or potatoes needs to be cured and dried, similar procedures should be followed. The temperature and moisture conditions of the curing and drying area will need to be maintained. The cleanliness of the area will need to be maintained and monitored. Injured or spoiled foods should be discarded before storage to minimize contamination. Before packaging, foods need to be dry brushed or washed, depending on the type of produce. When foods are packaged, they should be placed into clean containers that have been stored away from the ground in a sanitary place [Source 4].
For value added produce, rules about handling, preparation, and packaging will be different, although will share similar characteristics regarding the importance of sanitized surfaces, following agreed upon instructions and protocol, and temperature monitoring.
1) Personal communication with Phil Tocco, Michigan State University Extension service, 3/16/12
2) Aggie Horticulture Food Safety Training Guide. Accessed 5/18/12
3) USDA’s Grading, Certification, and Verification Page. Accessed 5/16/12
4) UC Davis Post-Harvest Practices Manuel for Horticulture Crops. Accessed 5/18/12