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Re-cooling of apples with water appears to be very efficient

Re-cooling of apples during the period of harvesting causes an enormous peak in energy. Engineering student Robin Beukers researched a method, which makes the cooling process quicker and more efficient. Apples are harvested once a year, although they are being eaten all year round. Therefore Dutch fruit growers prepare cooled stock cells, in which the apples are cooled down to 1 degree Celcius and stored under a controlled atmosphere. As a result the fruit remains good all throughout the year.

There is a big disadvantage to this method: the air installations in the cold stores use a lot of energy during the three week long harvesting period. As a result the fruit growers need a high capacity connection, which can handle the energy peak. Next to the cold store is a small transformer building, which is superfluous most of the year.

RCT-rivierenland, booster of innovation and mutual cooperation between companies in the agrarian environment and the production industry, organized meetings for entrepreneurs, who may have thought of a possible solution to this problem: with energy from sun panels growers could build their stock of ice during the Summer, which in the harvest season could be used to re-cool the apples. This would then no longer be done by cold air, but by means of a water bath.

Water has a number of positive properties. For instance less energy is required to decrease the temperature of the water than that of air. Also the apples would be cooled more evenly by means of water.

Bouw- en aannemingsbedrijf J.C. Van Kessel from Geldermalsen had HAN-trainee Robin Beukers involved in research on this concept. The student, however, came to the conclusion, that too much space is required for immersing the apples. Also the fruit crates are to be separated. That causes extra hours of labour or the purchase of extra machinery.

Therefore Beukers researched spraying systems. From calculations and tests it appears that this is almost as effective as a water bath. Beukers dipped a crate with apples with eight temperature readers inside under water. The hear of the apple reached the required temperature within fifty minutes. This decreased from 22 C. to 5 C. With sprayers this only took two minutes longer.

A revolutionary period. With present air cooling installations it takes from two to three weeks before the cell is full and the fruit has the correct temperature. The longer the apples remain warm the lower the quality of the apples. "Apples loose sugar when warm. The quicker they cool down the sweeter the fruit," says Beukers.

According to Edo Wissink, practice counsellor of Robin Beukers and researcher of TNO and HAN this system is of interest to growers who want to expand. That is because of the decrease in the requirement of cooling per ton of apples and the increasing capacity of the cooling. The present cooling installation then has sufficient capacity to build 30% more cells."

Source: Hogeschool van Arnhem en Nijmegen (HAN)

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