Growing year 2023 was one with challenges

After the growing season, harvesting also became almost as challenging as sowing in a number of regions. The results of the difficult growing conditions are reflected in storage. Tare percentages at delivery are higher than in a normal year, with "thick necks" being particular tare. Fortunately, onion prices are good and a good financial balance can still be achieved.

On the northeastern sandy soils in the Netherlands, especially Drenthe and Overijssel, onion cultivation has grown considerably in recent years. Every reason to look ahead to the new growing year 2024, from cultivation to storage, with a group of growers. Where previously the cultivation and especially shelf life of onions on sandy soils was viewed with suspicion, it has now been proven that the new onion growers have got the hang of it. Onion processors say they like the onions from these areas. Of course, there are also challenges here around climate and an ever-shrinking package of products to keep diseases and pests manageable.

Storage determines final cultivation yield

Besides knowledge of cultivation, the storage period in particular is a strong determinant of the final yield of onion cultivation. Reason enough to once again explain the basic principles of onion storage and also look at new developments. Onion storage mainly requires an understanding of the storage process. Quick drying, mould, bacteria and sprout inhibition are factors that affect storability. The storage process focuses on minimising the influence of mould and bacteria and extending shelf life. Indispensable tools for good storage are: fans, sensors and heaters/condensation drying technology. The essence of onion storage lies in measuring temperature and relative humidity both inside and outside and then taking thoughtful steps. The goal at every stage of storage is to reduce and keep the relative humidity low to keep the product dry.

Drying with outdoor air and heaters or condensation drying?

The first stage in the drying process is to heat the batch to ± 18-20 °C. This is necessary to create sufficient drying possibilities with outside air. The batch must be warm enough to allow drying with outside air during the day. When batches arrive at a warm temperature, this saves a lot of energy. It is important to avoid the 22 - 25 °C range because of the risk of expanding Botrytys causing rot. When the onions are at temperature, drying should be continued until a relative humidity of 65-70% is reached. This often takes about three weeks, after which post-drying begins and the number of hours of ventilation can be reduced.

This drying process can also be done with condensation drying. By first cooling down the air with a refrigeration unit (whereby the moisture in the air condenses) and using the released heat again to heat up the cooled air, drying can be done without using outside air. The great advantage is that drying can be carried out immediately, regardless of the onion temperature and the outside temperature. Even in periods when it is warmer outside during the day than in the storage area, a condensation drying system guarantees a constant drying speed. Drying can also be stopped when the onions have reached an R.H. of between 65-70%.

Have drying strategy determined by storage computer

With both systems, it is possible to dry onions quickly. Both systems have advantages and disadvantages. By drying with outside air and heaters, a higher moisture removal rate can be achieved at certain times than with condensation drying. With condensation drying, however, there is a continuous drying speed, so drying can be faster over 24 hours. A disadvantage of heaters is that they burn gas, with moisture entering storage. At outdoor temperatures higher than the onions, the drying speed can drop sharply and even become impossible. A condensation drying system is a big investment and requires a heavy power connection. However, both systems have advantages at certain times. Therefore, when investing in a condensation drying system for onions, the advice is to also invest in an automatic hatch system. The Vision Control climate computer can then determine which way of drying is fastest and will prefer (cheap) outside air. With the condensation drying system, outside air can also be heated so that heaters are no longer needed for this either. By cleverly deploying both systems, the result is a perfectly dry product throughout the storage season. Dry at any storage temperature, even at low temperatures during the storage phase.

Onion storage and tax benefit scheme 2024

The government in Europe often encourages investment in energy-efficient and sustainable techniques in agriculture. Modern mechanical cooling, condensation drying technology (heat pump) and energy-efficient fans Air Control MAX fall under this scheme. The EIA scheme offers a 40% deduction of the investment amount for entrepreneurs paying income or corporate tax in the Netherlands. Especially in a year when good financial results are being achieved, this scheme can be very attractive to make big strides in custody.

Contact our storage advisers directly to find out which storage system suits your situation best.