icon-blog Factory 6 Mar '18

Tasty potatoes can only be kept for so long

In our previous newspaper, we already discussed how we store potatoes post harvest and the factors that influence the successful storage and preservation of potatoes.  Over the years, the storage process has become automated and has changed significantly.  So how do we proceed?  Which parameters are important and how long can you store them?  Find out how to get the best out of stored potatoes. After harvest, a potato is still a living, natural product.  Various environmental factors in the shed are used to protect the natural quality of the tuber.  The most important factors are tem-perature, air circulation, oxygen level, sprout inhibition and the absence of any light.  Roughly speaking, the storage process has the following phases:

1. Wound healing and drying

 Clumps of earth and any adhering soil are  stored along with the potatoes in our sheds.  This generates additional moisture.  To be able to store the potatoes for longer, all excess water must be eliminated so the potatoes can dry.  This requires a good air circulation at a stable product tempera-ture of 12, 14 or even 16°C.  During the first weeks of the storage process, this temperature promotes wound healing.  During the harvest, the tuber may be damaged and these wounds must heal.  To achieve the right temperature and moisture level in the shed, you must achieve a delicate balance between internal air (air in the shed) and external air (outdoor air, whose temperature and moisture level changes daily). 

2. Cooling

Once the potatoes are sufficiently dry and the wound healing is completed, the temperature can be reduced, in a controlled manner, to the optimum storage temperature.  This cooling is a gradual process and lasts several weeks if the outdoor air is suited for this.  The optimum  temperature depends on the variety, but the majority of varieties used for potato fries have an ideal storage temperature of 6 to 8°C.

3. Further storage and tempeture control

The potatoes remain in their storage until they leave to be processed.  In the meantime, the farmer constantly monitors the potatoes and the environmental parameters to ensure that they remain as stable as possible.  During the  storage process, there are obviously storage losses. This is mainly weight loss, due to the drai-nage of excess moisture and the natural ageing process of potatoes.  
Depending on the number of months that the potatoes are stored, the storage process can be subdivided into three large periods.  The total storage loss can amount to 8 and even 10 percent of the potato weight. 
Nowadays the trend is to store potatoes for longer periods, while maintaining the quality that is required for potato fries.  Potatoes can be stored for up to nine months.  Farmers used the most modern storage sheds for this.

4. Storing potatoes: how, what and where 

Potatoes for potato fries are mainly stored in bulk. In recent years, however, more and more farmers are turning to crate storage for very long storage. There are various reasons for this: less bruising (soft spots on the potatoes because of the stacking), limitation of the storage risks and the option of storing various varieties with a similar storage temperature in one shed, without separating walls or split ventilation.  In the past, potatoes were stored in large sheds with thick, brick walls, which were insulated with straw.  Nowadays most storage sheds for bulk storage are made of concrete. Insulation and ventilation determine the climate conditions in the shed, for moisture elimination and tempe-rature control as well as for maintaining the oxygen levels. 

There are different types of ventilation:  

Natural ventilation: in traditional storage sheds, farmers can barely control the air  circulation, depending instead on the natural air circulation. The air circulates above the  potatoes, through opening hatches in opposite walls.  Here you are entirely dependent on the weather conditions.  In Belgium many potatoes that are stored for a short period of time are still stored in this way.  But the variety also matters. Bintje for example can be easily stored with  natural ventilation. 

Controlled ventilation (for crate storage and bulk storage): this type can be split into under-ground ventilation (the potatoes are stored on a concrete slatted floor ) and above-ground ventilation (the potatoes are stored on domes on a solid concrete floor).The ventilation  principle is the same but the controlled air flows in differently.  Weather conditions permitting you can also use natural ventilation in this type of storage.

Mechanical cooling : this is an additional option in a controlled, ventilated shed. Under normal weather conditions in spring, the  temperature in the storage shed will rise slightly to 9 or even 12°C even though the ideal storage temperature is between 6 and 8°C. To avoid this, the temperature in the storage shed can be  stabilised by cooling the air in the shed.  This principle relies on the good isolation and venti-lation of the shed. 
Farmers can use all kinds of modern equipment to assure optimum storage and checking of the environmental factors. They include storage computers, temperature measurement tools, humidity meters, CO2 meters and so on. They measure everything and control the fans and shutters. But in spite of all these modern tools, one of the most important factors when it comes to storing potatoes is the farmer’s experience, even though he also obviously depends on the weather conditions to some extent. 

Field tests

Like every year, Mydibel has prepared a test parcel this season.  We test and compare new, promising varieties and popular varieties (Bintje, Fontane, Challenger) in the field.  This year, the 4-hectare test parcel is located near the factory. It makes it easier for people to see the various varieties as they grow and we can monitor their development more closely.