Have you ever thrown out a carrot because it's been rotten in the bottom drawer of the fridge? Then you're not alone. In fact, almost 100,000 tons of fruit and vegetables are discarded every year in Danish households alone.

Carrots are one of the vegetables Danes eat the most of — and we also export large quantities of this popular vegetable to our neighbouring countries.

The potential to produce and export even more carrots is considerable—but one thing stands in the way: shelf life. Today, the average carrot has a shelf life of 12-14 days, but during part of the season, it can be less than one week.  This naturally limits how far away we can send this orange-coloured root vegetable.

A new research project called OptiClean has therefore set out to extend the shelf life of carrots by 7-10 days. The project is a collaboration between industry partners and Aarhus University and has received funding from the Green Development and Demonstration Programme (GUDP) of almost DKK 5.5 million.

From farm to table

After harvest, the carrots are cleaned to become the clean-scrubbed root vegetables we, as consumers, encounter in the supermarket.

When they arrive at the washing facility, they are carefully lowered into a large jacuzzi filled with water, where straw, stones, and soil are removed.

"Nozzles add air to the basin, which circulates the water. This means that the carrots move—and during the process, a substantial amount of dirt is removed," explains Associate Professor Merete Edelenbos, who has worked with carrots for almost 25 years.

The carrots are then transported into a drum with rotating brushes. This step is called polishing. Here, they are brushed so clean that they can be eaten almost as they are. The carrots are then cooled, sorted, and packaged in plastic bags to protect them from drying out.

Washing and polishing is a process that has both advantages and disadvantages, Merete Edelenbos explains.

"When the carrots are carefully washed, you can use them after a rinse and cutting off the top and bottom. We know that small snack carrots are eaten straight from the bag. Washing and polishing also make it easier for consumers to see the quality of the carrots in the shop," she says.

But the coin has a flipside.

"When carrots are washed and polished, the surface can easily be damaged, leaking carrot juice and making the carrot vulnerable to infections from the natural microorganisms on the root and in the wash water. This can lead to carrots rotting far too fast - and it only takes one rotten carrot to make the whole bag bad," the Associate Professor explains.

Cleaner process water and softer brushes

OptiClean will try to extend the shelf life of carrots by optimising two processing steps: washing and polishing.

The focus in the washing phase is on water quality. The researchers will try to purify the wash water with the naturally occurring gas ozone.

“If we can continuously purify the process water using ozone, we hope to improve the water quality and thus extend the shelf life of the carrots. In this process, we hope to decrease the nutrients available in the water and thus the microbial growth," says Merete Edelenbos.

During the polishing phase, several approaches will be evaluated, including the softness of the brushes, the carrot influx, and the speed of the drum.

The researchers hope that a combination of cleaner process water and less damage from the polishing process will improve the shelf life of the carrots.

To test whether the measures have had an effect, the washed carrots are subjected to a simulated journey to the consumers and then tested to see if they keep better.

Focus on microorganisms

One of the things that Merete Edelenbos finds especially interesting about this project is the analysis of the microorganisms in the wash water and on the carrot.

In the industry, microorganisms are seen as unfavourable because some cause root vegetables to rot. But when you remove these microorganisms, you remove them all. And we don't know if some organisms that are washed off positively affect shelf life.

"Not all microorganisms are harmful. That's why I think an interesting part of this project is to map out which microorganisms are in the wash water, and what each has to offer," explains Merete Edelenbos.

The analyses are carried out at Aarhus University. This is the first time we will analyse the specific microorganisms in the process water from washing facilities.

Wider potential

The OptiClean project started in August 2023, and producers at the washing facilities are already busy testing the first hypotheses. The results from the project are expected in December 2025.

If the methods are successful, they can likely be transferred to washing and polishing other root vegetables.

Are you interested in learning more about hygiene in fruit and vegetable handling? Then, join the OptiClean workshop at project partner FORCE Technology on May 23rd.