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Storing carrots: do it well or don’t do it

13 April 2021

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

Growing conditions have a major influence on the storage result of carrots. Especially the amount of rain and the disease pressure are strongly decisive.
The first aspect that will play a role in storage is the product temperature during harvesting. If the harvest takes place at a 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 must be removed during cooling. Twice the product temperature during storage requires twice as much time to cool down. In addition, the respiration heat is considerably lower at for example 8°C than at for example 15°C product temperature. The result: a considerably lower heat production. The difference between 15°C and 8°C is (75 minus 40 W/ton) 35 W/ton difference. In other words: approximately 45% lower respiratory heat and CO2 production. This also ensures that cooling takes even longer and that fungi have more opportunities to expand.

Every extra cooling action leads to extra moisture extraction from the carrot. Harvesting at a lower outside temperature therefore is profitable on both sides: less weight loss and lower energy consumption.


Regular refreshment

During cooling, but also during the storage period, regular air refreshment is required to keep the CO2 content low. This is because hardly any natural refreshment takes place due to the good insulation of the cells. High levels above 3% are really disastrous for carrot quality (and also for human health), which can cause visible damage. It is better to refresh at lower (0,5%) levels.


Cool fresh air

A disadvantage is that during the refreshment, ‘warm air’ is often drawn in, which means that additional cooling (and drying) takes place. One solution is to pre-cool fresh air. This is relatively easy with a Freshbox. This is a heat exchanger that cools incoming air with a low CO2 content with cold air from the storage area with a high CO2 content. Because of this unit, the air enters the storage with a lower temperature and a higher r.h. . This results in fewer operating hours of the mechanical cooling and ultimately in more sellable tons of carrots.


Choose natural refrigerants

The trend of the last ten years in mechanical cooling is the switch to cooling installations with natural refrigerants. New laws and 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 installation design

The choice of refrigerant depends on what one wants to emphasize with the cooling. Issues such as low energy consumption, minimal drying out of the product, in which (outside) climate the installation must function and which materials must be used that match the (sometimes high) operating pressures of the cooling system all determine the choice of a specific refrigerant.

Almost all of these natural refrigerants have better refrigeration properties than the synthetic refrigerants commonly used so far. However, the drawbacks that these refrigerants also have in terms of safety and toxicity will have to be reduced to an acceptable level by means of 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 refrigeration is used purely for carrot storage alone, or whether this refrigeration must also be able to store a cell with potatoes or onions at different temperatures. Direct and indirect cooling installations each then have their own area of application with advantages and disadvantages.



Get profit from stacking boxes

In addition to the cooling installation, there is also profit to be made in the use of the correct boxes and correct box stacking. Because a carrot box is not forced ventilated, there must be sufficient air circulation/ventilation between the boxes to eventually get the heart of the boxes to the same temperature. This only works with the correct stacking of the boxes. Logical? Yes, but in practice it gets too little attention. There may also be places where there is a short circuit in the air flow. As a result, some boxes are barely cooled in the end. This is illustrated in the enclosed top and side view of a box stack.



Higher storage return with a smart storage regime

Research has shown that a small temperature difference across the air cooler ensures less drying out. This drying out of the carrots was measured with electronic weighing boxes so that continuous weight loss could be measured.


The graph shows the difference between two settings. This is the difference between the air to be cooled and the evaporation temperature (= TV1). It was tested with a TV1 of 4 and 2,5 that is to say 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

To ensure an optimal storage climate and the same temperature and r.h. throughout the cell, there must be adequate air circulation/ventilation. This can only be achieved by installing sufficient air coolers in proportion to the cell width. Set these to run at the correct times via the storage computer. The advice is therefore to let the air cooler fans run continuously until the product has cooled down completely.

Concrete tips for optimal carrot storage:

  • Make sure that a healthy crop comes into storage
  • Choose an energy-efficient installation
  • Do not cut back on cooling capacity
  • Think carefully about the box stacking
  • Choose air coolers that have good cell coverage and lots of air circulation
  • Choose those air coolers that provide minimal dehumidification
  • Install and use the product temperature sensors to determine if the product is getting cold everywhere.

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