5 questions for Henk Tebben
Current storage technology is out of date
Is it wise to throw away the storage technology that has been used for potatoes and onions for more than four decades? That's what cooling specialist Engie Refrigeration is doing. Together with Aeres Hogeschool Dronten, it started a physiological study and arrived at a completely different storage concept from. The first practical results with potatoes are turning out well. Storage specialist Henk Tebben explains how the system works.
The name Engie Refrigeration may not immediately mean something to you. In March 2016, technical service provider Cofely continued under a new company name. Previously, the company was better known under the names Zephyr and GTI Koudetechniek. Project manager Henk Tebben is closely involved in the first potato storage according to the new concept, which the company has built in Germany.
You throw technology that has been used in agriculture for decades to the side and come up with something completely different. How is that possible?
'The storage technology that is now being used in agriculture is forty years old and no longer up to date. The established order has grown from the sale of fans. They keep doing that. We spoke with many arable farmers beforehand, looked at existing technology and examined the products. An architectural and technical design was then made to answer the question: what does the optimal storage look like? We already have a lot of experience in mushroom cultivation. For example with steering on CO2. We have extended the use of optimal storage conditions to the potatoes. After all, different storage conditions apply to each product.'
What are the most important results of your research into optimal product storage?
'Rule one in agriculture is still: ventilate with as much outside air as possible. Then you are always adjusting, depending on the outside temperature. With cold air from outside that is not such an issue, but the climate is changing and the air conditions are far from optimal. On average, the temperature is too high. An air flow of 250.000 cubic meters per hour – which is recommended in practice – makes no sense. You are often firing with propane gas. When one kilogram of propane gas is burned, 1,6 liters of water are produced. You have to vent all that out. When the potato gets warm, it sweats and produces sugars. That comes at the expense of quality. With our storage concept we aim for a fixed CO2 value, a fixed temperature and a fixed RH value. The situation is slightly different with onions, because you still have a lot of drying to do after they have been brought in. However, here too, too much dehydration costs kilos.'
How do you ensure that the product does not sweat and eventually lose weight?
'After the harvest, we dry the skins as quickly as possible. Pre-drying with outside air, for example putting boxes in a draft, is not necessary. We look at the type of potato, tare and moisture content. The properties of the product are entered into the storage computer and monitored during the process. After a week the wound healing starts, whereby we close the so-called 'coat' of the potato. You will then no longer lose any moisture. The dehydration during the entire storage period amounts to a maximum of three percent. The CO2 content is measured. If it exceeds a certain PPM value, a small fan extracts it. If the temperature is stable, hardly any more CO2 is produced. Internal ventilation is required periodically. The product is kept at a constant temperature until July. Warming up before sanding is unnecessary in some cases, because the skin of the potato is completely closed. That has to be done with chips potatoes.'
1,6
liter of water
Much has been invested in storage technology in recent years. Do arable farmers have to change tack, resulting in high costs?
'Depending on the situation, the system can also be built in an existing storage facility. The air must be dehumidified and treated with evaporators. This requires a completely different layout of the shed. Fans and hatches are unnecessary. Therefore, take a good look at the costs to see what is cost-effective. Our storage method does not have to be substantially more expensive than traditional storage. The results are best when stored in boxes, but bulk is possible. This does require fans and more cooling capacity. With crates you can dry the product from different sides. Changing the temperature one degree costs you three percent of energy. With the heat carriers we can save up to fifteen percent energy. And then there are the benefits of your product. We estimate that after three seasons you will have recouped the additional costs of the Engie storage system.'
Last season, Engie built the first installation on an arable farm in Germany. How did that work out?
'This German potato grower processes its own potatoes for the consumer market. Previously, the product remained good until March. Then everything had to go out. Waste rates of up to fifty percent were not uncommon. With his new product storage, the potatoes were stored until July and they came out of the crate in mint condition, with hardly any storage losses. Pressure spots do not occur. Nests with rotten tubers are gone. That's because the tubers have been mummified. A fungus does not expand below four degrees. All of this immediately generates money. In addition, the German government requires cooling installations to meet a certain energy efficiency. This installation meets all requirements. You can heat a canteen with the residual heat produced by the chillers. That also saves on costs. There is a lot of interest in the German pilot project. A second project, in the Netherlands, is now in the pipeline.'
Niels van der Boom
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