Proper handling of crops after they have been harvested can extend their storage life and help to retain their flavor, nutrient value and marketability long after being plucked. Even the brightest tomato on the vine or the crispest head of lettuce growing in a hydroponic set-up can become quickly worthless if proper post-harvest practices are not observed. The care taken in produce handling and storage will help to prolong the potential longevity of harvested crops. The likelihood of food-borne illness is also greatly reduced when safe food-handling protocols are followed. For food quality and safety, a few key guidelines should be followed.
Crop Harvest Considerations
How and when your crop is harvested can add hours or days to its useful post-harvest viability. Three degenerative conditions should be avoided to prolong your crop quality: heat injury, water loss and premature senescence (ripening and maturity). If growing field crops, it is best to harvest during the coolest time of the day; in most cases, this is the early morning. Harvesting can also be done though in the evening hours or during periods of cloud cover in the daytime. Plants and produce “breathe” much like you and I. The hotter it gets, the more the produce respires moisture. Because the harvested crop has been detached from its plant or pulled from the ground, it cannot replace the moisture it loses as it respires. The water loss of produce marks the beginning of the end of its quality. Drier produce is less sweet and for those who make their living selling crops, dry crops also yield less weight.
Care should be given to ensure that produce is not physically damaged during the harvest. Harvesting tools, fingernails and branches from other plants can easily bruise the skin of several different types of produce. In addition to the appearance that will suffer (important if you are selling your crop), wounds to the produce can become the entrance point for several disease pathogens like bacteria, fungi, yeasts and insects.
If your harvest schedule does not allow for harvesting during darker or cooler times of the day, and for the immediate cleaning and storing of your culled crops, make sure they are fully shaded as they lay in wait for these next few important steps.
Cleaning and Sorting Crop
Cleaning is a critical post-harvest step, not only to remove field debris and to remove any foreign objects or insect pests from your crops, but to remove as much stored heat gained from being out in the open field as possible by pre-cooling the harvested items with water. In this instance, well water is preferred as it usually comes out of the ground between 50-60°F, but any water is better than no water for this task.
Besides water alone, there are several products that can be included in the cleaning and sanitizing of harvested crops that are safe to use and are even approved in the production of certified organic crops. Acetic acid, ethyl alcohol and hydrogen peroxide can all be used to clean produce and reduce the risk of pathogens such as E. coli, salmonella and listeria.
At the cleaning stage, it is important to be selective about what goes on into storage. Produce that is already over-ripe or under-mature should be separated out. These will not last as long as produce picked at the proper time.
Bruised produce should be separated as well before heading into storage, as punctured skin invites disease that can quickly spread to the other produce. Less than perfect produce does not have to go to waste.
So long at it is used quickly, it can be used in soups, smoothies or any other form where appearance is irrelevant. There are also many organizations of gleaners that will gladly come to your site and collect any such produce to be used in public food banks and the like.
Temperature is the most important component to prolonging the stored life of harvested produce. Most harvested crops should be stored at about 40°F and in no instance below 32°F. For every increase in temperature of 18°F (above 40°F), the rate of decay of stored produce increases by a factor of between two and three. Of course, there are always exceptions.
Many have certainly put their tomatoes or freshly harvested basil in their refrigerators only to find them less than palatable-looking upon their retrieval. Tomatoes, basil and eggplants are very sensitive to cold storage.
These items should be kept at about 70°F for optimal usage. Other crops are not quite so sensitive, but don’t keep as long when cold-stored for prolonged periods. These include potatoes, peppers, cucurbits (squash, pumpkins, cucumbers), beans and peas. If possible, store these items at about 50-55°F.
Temperature fluctuations should be avoided as much as possible as well. Even if the harvested crops are held at a stable temperature, accessing them by continual opening and closing of the door or port can cause too much of a range in temperature. Access your storage containers or rooms only when it is necessary. When produce is exposed to frequent variances of cold and warm temperatures, moisture can accumulate on their surfaces. This sets the stage for various fungal pathogens or diseases to develop.
If you lack a suitable storage area for short-term storage, some crops will do well when packed with ice. The range of crops that can tolerate ice contact versus those that are damaged by contact with ice is a lengthy one. A few common crops that can be stored with ice are beets, carrots, green onions, radishes, spinach, leafy greens and sweet corn. A few that are damaged when stored with ice are berries, tomatoes, squash, garlic and bulb onions. Consult your local extension service to be sure which crops in your particular region and climate can be stored with ice.
Second only to temperature in importance to prolonging your harvest is air circulation. When stacking containers of stored produce, make sure that they are not so close to one another or to the walls that air cannot circulate around them. Put spacers between containers if the containers themselves lack adequate vents. If you are storing loose produce in a cooler or cold space, make sure it is spread out as much as is practical.
Humidity is another important factor to consider when storing crops. Try to raise the humidity of your storage area by dampening the floor before placing the produce on it. Produce can also be sprinkled with water periodically, or you can place a damp cloth over top of the harvested items during their storage period.
When storing harvested crops of varying quality, do not co-mingle. As crops ripen, they release ethylene gas, which in turn encourages further ripening of nearby crops. Think of the expression “one bad apple spoils the bunch.” This refers to the ethylene that a ripening fruit or vegetable is releasing. There are other sources of ethylene that can cause the premature ripening of your crops. Make sure your produce is not stored near a compost pile or where it may come into contact from the combustion of fuels such as propane.
For long-term storage of one month to one year, it is critical to maintain the right combination of temperature and humidity, and to only store produce together that has like requirements. Most produce prefers low temperatures with high humidity, while some require higher temperatures with low humidity; others need some combination of the two. Here are some typical combinations of storage conditions for long-term produce or crop storage:
- The majority of root crops such as beets, carrots, turnips and leeks store best at about 32°F with 90 per cent humidity.
- Bulbs such as garlic and onions like the same temperature (32°F) but require only 65-75 per cent humidity.
- Potatoes and winter squashes are both happy at a range between 40 and 60°F but need humidity levels at 90 per cent and less than 60 per cent respectively.
It probably goes without saying, but all harvested crops or produce needs to be packaged in clean, well-ventilated containers. If reusable containers are employed, ensure that they have been thoroughly sanitized. As seemingly wasteful a practice as it may be, do not re-use cardboard produce boxes to re-package produce. Those same boxes can of course be re-purposed for other uses, but food storage should not be one of them.
Once damage to your crop occurs after it has been harvested, there is little to nothing that can be done to restore it. Proper post-harvest procedures begin even before the time of harvest. Proper selection of seed, plants and sites will pay huge dividends on the back end when it comes to prolonging the life of stored produce in your particular climate.