Postharvest handling of fruit and vegetable crops in Minnesota

Air cooling relies on cool air moving around the product. This is typically done in a walk-in cooler but can be as simple as putting harvested product in the shade. Most fruits and vegetables can be air-cooled.

For more information about building a walk-in cooler, see this guide from the University of Kentucky. If a grower has the capacity to build a cooler, this is typically the easiest option.

This method uses cool, clean water to bring the temperature of the produce down. This can be done either with a spray table or in a dunk tank.

Only produce items that can withstand water should be cooled. Only potable water should be used in postharvest washing.

The tanks and spray tables should be cleaned and sanitized regularly. Use a sanitizer in the water to reduce the potential for cross-contamination between crops.

For more information on sanitizers see the washing section below.

Some produce can be cooled with ice, but make sure the ice you use is made from drinking water. One option is to attach an ice maker to a potable water source and make ice on-site. You can also buy chipped ice (which can be expensive).

You can cover products such as brassicas, root crops and sweet corn with ice, letting any excess water drain from containers.

Take care to provide proper drainage in the storage room to avoid slip hazards and water accumulating as the ice melts.

• Field curing can be done if warm (~ 80-90 °F), rainless days are forecast at harvest time.
• Sever the product from the rest of the plant and lift the product out or off of the ground.
• Lay the product on top of the soil and let it cure in the field for 7 to 10 days, or until the wounds scab over or onion necks dry.

Indoor curing is recommended if weather will not be amenable to field curing. This can be done in any covered facility (like a barn or high tunnel), as long as outside air is circulated past the product. Open doors and use fans to promote airflow.

Garlic and onion plants are often tied together and hung from rafters, but they can also be laid out on benches. If the benches are not perforated, make sure that produce is rotated periodically so that all areas are exposed to warm air (~ 80-90 °F).

Good air circulation is crucial for proper curing.

Onions and garlic

• Onions and garlic are done curing when the necks are dry, which usually takes 3-4 weeks.
• After curing is complete, brush lightly to remove loose skin and dirt. At this point the roots and stems should be trimmed for longer-term storage.
• Sort thoroughly before moving onions and garlic to longer-term storage, and remove any bulbs with soft spots.
• Read the Growing Garlic in Minnesota guide for more detailed information. 

Pumpkins and squash

• Pumpkins and squash are done curing when nicks and small cuts are scabbed over.
• As a rule of thumb, the squash is done curing once it cannot be punctured with a fingernail.
• They should be wiped with a clean rag after curing. 

Potatoes and sweet potatoes

• Potatoes and sweet potatoes are done curing when wounded areas are healed.
• After curing, they can go directly into longer-term storage, and washed when they are ready to sell.
• Sort thoroughly and remove any potatoes with soft spots, black or brown cavities, or unhealed cuts and bruises. 

• Spray tables are useful for spraying root crops and other hearty vegetables with larger amounts of soil that can tolerate spraying, like bunched crops like radishes and beets.
• This system uses a single pass, which does not recirculate the water, reducing the potential for cross-contamination between crops if there is any contamination from the field.
• The tables can be constructed from 2x4 lumber frames with some sort of a porous top such as a screen, rigid plastic greenhouse bench, plastic-coated hardware cloth or other materials that allow water to flow through.
• Use a hose with a spray nozzle to spray the crops and allow the water to flow away from the crops and to a drain.
• The food-contact surfaces on the top of the table should be constructed from materials that are smooth, durable and easy to clean and sanitize.

• Bulk tanks are used to rinse and cool produce in some sort of sink, tank or tote.
• Wash tanks can be used with most types of produce (beans, cucumbers, leafy greens, slightly dirty root vegetables, peppers, baby potatoes, radishes, summer squash, apples, etc.) that can be dunked in water.
• When washing in a bulk tank, always start with a clean and sanitized tank.
• Change the water frequently to ensure that the water does not have excessive organic matter build-up.
• A tank that has a drain will allow you to more easily change the water.
• After an initial rinse to remove soil and debris, it is a good idea to use sanitizer in subsequent rinse water tanks to reduce the potential for spreading contamination via the water.

Use sanitizers to reduce cross-contamination between products in the water. Each sanitizer product (e.g. bleach, SaniDate, etc.) will have specific instructions on the label for the proper concentration or rate to use.  See more information on using sanitizers in wash water from the On-Farm GAPs Education program.

Be sure that the wash water is not more than 10 °F cooler than the product. This will help prevent any pathogens in the wash water from getting sucked into the produce via the stem ends, cuts or bruises via a process called infiltration.

Other types of washers include barrel washers and brush washers.

• Barrel washers are used for root crops, and work by tumbling the crops around through the barrel while streams of water wash them.
  • The soil is moved away via the water and the roots come out the other end of the machine with the bulk of the field soil removed. 
• Brush washers are used for any type of produce that needs washing and is not delicate (leeks, radishes, slightly dirty root vegetables; adjust the flow rate to the delicacy of plant tissue).
  • This equipment uses jets to spray water over the produce and send it through brushes to wash it.