I’m not going to lie, post-harvest handling of fruits and vegetables is a rabbit hole that will take you to strange and fascinating places. What happens to plants after they’re picked is not as simple as it appears on the surface. Leaves turn toward the sunlight, sugars transmogrify into new shapes, cells grab at moisture and gases. And all these changes affect harvested plants before we eat them – for better or worse. A basic understanding of the forces at play will help you to maximize the abundance of your harvest in any climate or season.
There’s something alive in my fridge!
Everything lives and dies a little differently. Animals have fixed life spans, which end at a finite point in time. Some microbes, like bacteria, have no programmed death and under the right conditions can divide indefinitely – essentially living forever. Plants, including fruits and vegetables, lie somewhere in between on the scale of life and death. Plants die slowly, over time, through a process called senescence.1
When you eat produce picked fresh from the farm, it is still very much alive. Its cells are actively metabolizing and respiring. Once a fruit or vegetable has been picked, however, it loses its source of nutrients, and its cells slowly begin to die and degrade. As the cells senesce (die slowly) it loses its vibrant appearance and eventually begins to spoil.
You can prolong the life and vibrancy of your living produce by handling and storing them in conditions that slow senescence.
Understanding Post-Harvest Life
All living things, including plants, have a direct and dynamic relationship with the non-living world around them. They take in gases, water, and nutrients and transform them into energy for growth. Although vegetables may appear to move and grow slowly and once picked look completely inert, they are wildly interactive with the world around them.
Respiration and Water Loss
Fruits and vegetables use oxygen to help create the energy they need to build and maintain their cellular structure, develop flavor, and grow and ripen. This is respiration. Once a fruit or vegetable has been picked, its source of nutrients are gone, but its cells continue to respire. Therefore, faster respiration rates in fruits and vegetables result in quicker degradation of the plant, loss of food nutritional value, overall weight loss, poorer flavour, reduced quality, and faster senescence.
Some fruits and vegetables naturally have a lower respiration level than others. Potatoes, apples, and squash are actually reproductive bodies that are well equipped to last for long periods of time under cool conditions – they have very slow respiration rates. Other types of plants, like leaves of lettuce and broccoli florets, have very high respiration rates and must be eaten quickly, no matter how they are stored. (Although proper storage will maximize their lifespan.)
High levels of respiration also contribute to water loss, which is what causes fruits and vegetables to reduce in weight, wilt, shrivel, and lose their crispness.
The simplest way of reducing respiration and water loss is by cooling. You can increase the storage life of many fruits and vegetables by cooling them quickly in a refrigerator but not all. Some fruits and vegetables, especially those that have evolved from tropical climates, are cold sensitive. This means they will actually develop irregular ripening and decay faster under refrigeration than at room temperature. Tomatoes, eggplant, and cucumbers are common examples of chilling-sensitive vegetables.
Ethylene Production and Ripening
Another factor that affects post-harvest lifespan is the production of and exposure to ethylene gas. Ethylene is a plant growth regulator that is produced naturally by many fruits. For some fruits, ethylene production is essential for ripening. For others, exposure to ethylene causes a dramatic increase in respiration, leading to faster senescence. Therefore, fruits and vegetables that produce ethylene should never be stored with those that are sensitive to it.
Spoilage is caused by two things, often at the same time: physical degradation and microbial transformation. Physical degradation occurs as harvested plants senesce naturally or are damaged. These types of changes are seen as the browning of an apple slice or darkening of a bruised leafy green.
Microbial transformation happens when microbes present on the fruit or vegetable transform its nutrients into energy. As they grow, you may see masses of them and their byproducts in the form of hairy mold or slimy sludge. When harvested items are physically damaged by bruising, crushing, cuts, or excessive moisture, they are particularly susceptible to microbial transformation. Spoilage on one piece of produce quickly affects more. Always eat damaged fruits or vegetables right away before they spoil further.
Soil quality and mineral composition also greatly affect storage life. Decreased mineral content and excessive applications of nitrogen on large scale commercial farms can produce big vegetables, but generally decreases storability and post-harvest quality. Large commercial operations also often rely on chemicals, waxes, dyes, and synthetic growth regulators to ‘maximize’ fruit and vegetable shelf life. Unfortunately these practices also often minimize the nutritional and health value of these foods. If you don’t grow your own, buying fresh produce from farmers who nurture their soil will always be a the best option.
Five Fruit and Vegetable Storage Tips
You can easily extend the life of your fruits and vegetables by taking some very simple measures to keep them fresh and vibrant.
1. Always eat produce with the shortest natural storage life first.
2. Store produce quickly and at the right temperature.
3. Keep ethylene producers away from ethylene sensitive produce.
4. Eat physically damaged fruits and vegetables right away before they spoil.
5. Grow your own or purchase from small farmers with high quality soil.
Laura is the Director of Food Systems and Fermentation at Rancho Mastatal Center for Sustainability Education in Costa Rica, and a Food Systems Consultant for Round the Bend Farm Center for Restorative Community in Dartmouth, MA.
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