The increasing importance of grain preservation

Due to severely fluctuating weather conditions, grain preservation grain preservation is becoming more and more important in agriculture. Chemical preservation with suitable acids has become well established. This is now the most efficient and cost-effective process. However, not every user knows how preservation with acids actually works. AGRAVIS expert Dr. Sabine Rahn explains in an interview what needs to be borne in mind.

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Which acids should you use?
Dr. Sabine Rahn
: The active ingredients used in grain preservation are ones that primarily combat mould. Bacteria and yeasts are only responsible for spoilage in extremely rare cases, due to the moisture content of the stored grain. The active ingredients should be selected accordingly. Propionic acid is still the key grain preserving agent. When used correctly it can reliably preserve the treated grain. Those who shy away from pure acid as too corrosive use Grain Save NC for preservation. NC stands for "non corrosive". Unlike concentrated, pure propionic acid, Grain Save NC is buffered with ammonium. This makes it a user-friendly, but nonetheless very effective product (90 percent PS, pH value 4.1). Because of its special product formulation, Grain Save NC is less corrosive, which saves milling and mixing plants and grain stores from damage. Grain Save NC is also not a hazardous substance. There are therefore no quantity restrictions for transport.

How does preservation with propionic acid work?
Dr. Sabine Rahn
: Propionic acid works against micro-organisms in three different ways. Firstly, pure propionic acid reduces the pH value on the grain surface so much that the growth and reproduction of certain micro-organisms are no longer possible, or only possible to a greatly reduced extent. In addition, the non-dissociated acid molecule is able to penetrate the cell wall of micro-organisms, thereby reducing the pH value inside the cell and also the osmotic pressure, which leads to the death of the cell. Propionic acid also blocks the enzyme metabolism of the microbial cells and stops them from reproducing. The pH value combined with the active acid content is crucial for effectiveness. The higher the pH value, the less microbially effective the acid is and/or the higher the dosage needs to be. For example, if the proportion of active acid is 90 percent, the application rate must be increased by ten percent.

What happens if the amount of the active substance is below the requirement?
Dr. Sabine Rahn
: The correct dosage is important for effectiveness. This includes determining the correct application rate and ensuring precise distribution. Dosing tables help to determine the application rate depending on the grain moisture content and storage time. If you are using a buffered version of an acid, the application rate can be calculated from the table based on the content of the active substance combined with the pH value of the product. It is important not to apply too low a dose. If the acid dose is too low, store stability is uncertain, mould grows again and the grain is spoiled. The presence of preserving agents puts moulds under stress. Moulds react to stress situations with increased formation of mycotoxins. To control this risk, the dose of preserving agent must be sufficient. If the application rate is too low, this causes them additional stress. The risk of mycotoxins increases.

What role does "outgassing" by the acid play?
Dr. Sabine Rahn
: The phenomenon known as "outgassing" plays only a very insignificant role. Occasionally, the preserving effect of propionic acid is incorrectly associated with its "outgassing". The gases are supposed to penetrate the grain pile and thus protect it from spoilage. However, this is not how the preserving effect works. Propionic acid and Grain Save NC are only present as a pure and free product for a very short time after application. They react relatively quickly with the microbial cells outside and inside the grains. Within a short time, the free acid is absorbed by the grain kernel; the grain is dry on the outside and can be stored in any store without problems. If the acid continued to outgas, this would not be possible. Acid in the emitted air would, for example, lead to a significant amount of corrosion damage.

Is any of the acid lost during storage?
Dr. Sabine Rahn
: No. Propionic acid and Grain Save NC are not lost during storage, provided they are correctly dosed. Numerous studies prove this. The quantity of acid in the treated goods has been proven to remain the same throughout the whole storage period. This ensures its preservation status. This is only not assured over the long term if the dose is too low and the propionic acid is broken down by the micro-organisms.

When does more acid need to be added?
Dr. Sabine Rahn
: More acid needs to be added, for example, when the preserved grain needs to be conveyed by means of blowers. The recommended application rate in the dosing table then needs to be increased by at least 10 percent. If the grain is stored at very high temperatures (> 35 degrees), 10 percent additional acid is recommended. At these high temperatures, some of the acid may evaporate. Increasing the application rate by 10 percent compensates for this.

Can grain batches with different moisture content be stored together?
Dr. Sabine Rahn
: No. Batches with different moisture content or which have been treated differently should not be stored together. The water from the more moist batch can infiltrate the drier batch, which can then become spoiled.

Can you mix acid with Actellic or K-Obiol?
Dr. Sabine Rahn
: Yes. These can be mixed with no problems.

How long must the grain be stored before it can be used as fodder?
Dr. Sabine Rahn
: Regardless of whether it is preserved or not preserved, freshly harvested grain should not be used as fodder immediately. Preservation with propionic acid does not change this.

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