Storing carrots: do it right or don't do it

Carrots don't have a peel or skin like a potato or onion. In storage, the product is therefore not protected against attack by fungi and bacteria. That makes storing carrots quite difficult. It requires a specific approach, because there are virtually no correction options available to prevent further damage.

Cultivation conditions have a major influence on the storage result of carrots. The amount of precipitation and the disease pressure are particularly determinative. The first aspect that will play a role in storage is the product temperature during storage. If the harvest takes place at high soil temperature and humidity, the start of storage will be more difficult. Cooling then takes longer because both the heat from the product and the moisture from the adhering soil have to be removed during cooling. A 2 times higher product temperature during storage requires twice as much time to cool. In addition, the respiratory heat is considerably lower at, for example, 2 °C than at, for example, 8 °C product temperature. The result: a considerably lower heat production. The difference between 15 °C and 15 °C is (8 minus 75 W/ton) 40 W/ton difference. In other words: approximately 35% lower respiratory heat and CO45_-production. This also ensures that the cooling process takes even longer and molds have more opportunities to expand.

Every extra cooling action leads to extra moisture extraction from the carrot. Storing at a lower outside temperature therefore yields benefits on 2 sides: less weight loss and lower energy consumption.

Refresh regularly
During cooling, but also during the storage period, it is necessary to refresh regularly to keep the CO2 content low. There is hardly any natural renewal due to the good isolation of the cells. High levels above 3% are really disastrous for carrot quality (and also for human health). This can cause visible damage. It is better to start refreshing at lower (0,5 %) levels.

Cooling fresh air
A cooling technical disadvantage is that 'warm air' is often brought in during the change, which means that additional cooling (and drying) is done. One solution is to pre-cool fresh air. This can be done relatively easily with a Freshbox. This is a heat exchanger that cools incoming low-CO2 air with cold air from the high-CO2 storage area. Through this unit, the air with a lower temperature and a higher RH enters the storage. This results in fewer operating hours of the mechanical cooling and ultimately in more salable tons of carrots.

Choose natural refrigerants
The trend of the last 10 years in mechanical cooling is the switch to cooling installations with natural refrigerants. New laws, regulations and tax incentives have accelerated this trend. The refrigerants ammonia, propane and CO2 are the most commonly used, both in direct and indirect installations.

Smart plant design
The choice of a refrigerant depends on what you want to emphasize with the cooling. Matters such as low energy consumption, minimal drying of the product, in which (outdoor) climate the installation should function and which materials should be used that match the (sometimes high) working pressures of the cooling system, all determine the choice of a specific refrigerant. .

These natural refrigerants almost all have better cooling properties than the synthetic refrigerants commonly used until now. However, the drawbacks that these refrigerants also have in terms of safety and toxicity will have to be reduced to an acceptable level through a smart design of the cooling installation and the correct choice and application of the materials. The overview compares a number of properties of natural refrigerants.

The choice of a specific refrigerant also depends on whether a cooling is used purely for carrot storage alone, or whether this cooling must also be able to store a cell with potatoes or onions at different temperatures. Direct and indirect cooling installations then each have their own field of application with advantages and disadvantages.

Get profit from the chest stack
In addition to the cooling installation, there is also benefit to be gained from using the right boxes and correct box stacking. Because a root box is not forced to ventilate, there must be sufficient air circulation/ventilation between the boxes to eventually also get the heart of the boxes at the same temperature. This only works if the boxes are stacked correctly. Logical? Yes, but it still gets too little attention in practice. There may also be places where there is a short circuit in the airflow. As a result, some crates are hardly cooled in the end. This is illustrated in the attached top and side view of a crate stack.

Higher storage yield with smart storage regime
Research has shown that a small temperature difference across the air cooler results in less dehydration. This drying of the roots was measured with electronic weighing boxes so that weight loss could be measured continuously. The graph shows the difference between 2 settings. This concerns the difference between the air to be cooled and the evaporation temperature (=TV1). This was tested with a TV1 of 4 and 2,5, ie a difference of 1,5°C. After 23 weeks of storage, this has translated into a lower weight loss of more than 1,1%.

Sufficient air circulation
In order to obtain an optimal storage climate and an equal temperature and RH in the entire cell, there must be sufficient air circulation/ventilation. This is only possible by installing sufficient air coolers in proportion to the cell width. Set them to run at the correct times via the storage computer. It is therefore recommended that the air cooler fans run continuously until the product has cooled down completely.

Concrete tips for optimal root storage:

• Make sure a healthy crop is put into storage
• Choose an energy-efficient installation
• Don't skimp on the cooling capacity
• Think carefully about the box stacking
• Choose air coolers that have good cell coverage and plenty of air circulation
• Choose those air coolers that provide minimum dehumidification
• Install and use the product temperature sensors to determine if the product is getting cold everywhere

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