Packaging is more than just casings to put something in, it also extends the shelf life of fruit and vegetables.

Two packaging experts explain how this works.

As soon as a horticultural product loses between 3 and 5 percent of moisture, it loses its freshness.

"The cell voltage decreases, making the product less crispy," says Ernst Woltering, professor of product physiology and product quality at WUR.

"A cucumber will feel limp and lettuce will wilt."

This is purely the result of evaporation.

Fruits and vegetables contain a lot of water.

Moisture goes to the environment because the air is much less humid.

"By packaging the product in plastic, the air in the plastic bag quickly becomes as humid as the product itself," says Woltering.

"You create a moist microclimate around the product, which stops evaporation."

Many vegetables are packed in the store.

Many vegetables are packed in the store.

Photo: Shutterstock

Fruits and vegetables live on after they are picked.

They still absorb oxygen, release CO2 and burn sugars.

Woltering: "This so-called respiration rate can be slowed down by lowering the temperature."

By keeping them in the fridge, for example.

Products can take longer with their sugar supply, and therefore stay fresh longer.

Another way is to lower the oxygen content.

"This often happens in bags of pre-cut vegetables and trays of fruit salad," says packaging specialist Wouter de Heij.

"Normally this is about 20 percent in the open air. We reduce this to a few percent, and we increase the CO2 slightly, from 0.04 to 4 percent."

Such packaging can be recognized by 'packed under a protective atmosphere' on the label.

Woltering: "Just before sealing the bag, a gas mixture is injected. That may sound scary, but it is not. These are gases that are simply in the air, but in a different composition."

"If the moisture content in the factory is too high, condensation will form in the packaging during cooling."

Wouter de Heij, packaging specialist

Storing too long produces moist pre-cut vegetables.

"When the sugars are used up and breathing stops, there is no more energy to maintain the cell structure. The water from the cells comes out," says De Heij.

"Moisture in the packaging can also be due to the packaging conditions. If the moisture content in the factory is too high, condensation will form in the packaging during cooling."

Incidentally, there is also a changed atmosphere with broccoli or cucumber in foil.

"Because the product absorbs oxygen, the oxygen content in the small space between plastic and product is also lower than normal," explains Woltering.

"The plastic foil therefore contributes to the shelf life in two ways."

Packaging with holes

And then there are packages with holes in them.

What are they for?

"There are roughly two types: macro and micro perforations," says De Heij.

At the micro-perforations, holes of between 30 and 100 micrometers ensure that as much oxygen enters as the product uses.

"This 'controlled leakage' prevents the oxygen content from becoming 0, because that is not beneficial for the freshness of the product."

See also: The Dutch consume 26 billion plastic food packaging annually

Macro perforations are a mistake, according to De Heij.

"In theory you would use them with products that have the best shelf life at an oxygen content of just 20 percent. But there are actually none. In short, there are better ways to keep strawberries or blueberries fresh for longer."

Would we actually be able to do without plastic packaging?

"I think this is difficult," said Woltering.

"Fruit and vegetables would then have to be stored at a low temperature and high humidity throughout the chain. There are movements in that direction: think of fog installations in the fruit and vegetable department of some supermarkets."

Storage tips:

  • Once at home, leave the packaging around fruits and vegetables.

  • Keep fruit and vegetables as much as possible in the vegetable drawer of the refrigerator.

    Because it is sealed, the moisture in the drawer rises and this reduces the evaporation of moisture from the products themselves.

  • Place pre-cut vegetables and meal salads in the refrigerator as soon as possible.

  • If you use a piece of cucumber, leave the plastic around the remaining part.