Harvesting and drying hazelnuts to reduce aflatoxin risk

Reducing aflatoxin risk in the field means moving harvested hazelnuts promptly into appropriate drying conditions and protecting them from rewetting afterwards. The plan involves more than asking how many days they were dried. Maturity, rain exposure, holding conditions, measurements and storage entry should be considered together. Our first article explains aflatoxins and provides the background for these controls.

Plan harvesting and drying capacity together

The Hazelnut Research Institute explains that prematurely harvested nuts contain more moisture and require longer drying. Soil contact also matters for microbial load. Choosing the harvest date solely around workforce availability can create additional work at later stages. (Hazelnut Research Institute)

Before harvesting, consider drying capacity and a wet-weather plan. Decide where incoming nuts will be handled, how different harvest days will be identified and which space will be used during poor weather. These questions create a practical working plan for managing delays when volumes are high.

The Ministry's technical guide recommends collecting fallen nuts promptly, using clean breathable sacks, moving the harvest to the drying area on the same day and avoiding damp piles. Rain covers should preserve airflow. (TAGEM technical guide)

Drying depends on how the process is managed

Guidance from the Ordu Provincial Directorate highlights spreading nuts in thin layers and stirring them. Wet nuts should not be left in sacks; damaged nuts should be separated and warm nuts should not be bagged immediately. (Ordu Provincial Directorate)

Managing drying requires more attention than waiting for a predetermined date. Changes in rainfall, layer thickness and use of the drying area require reassessment. “It looked dry yesterday” cannot replace a measurement for the nuts entering storage today. Checking only an easily accessible surface does not resolve the question of whether the observation represents portions that dry more slowly.

A decision at the end of drying can be recorded: which lot was measured, when, using which instrument and against which specification? These are suggestions for organizing production information, rather than a standalone certificate of compliance.

Moisture content and water activity answer different questions

Moisture content describes the amount of water in a product. Water activity describes a property related to its availability to microorganisms. Two foods with the same moisture content can have different water activities. Applying one universal moisture percentage to every hazelnut form is therefore not an appropriate control approach. (USDA ARS)

Water activity is defined by the product's water vapour pressure relative to pure water at the same temperature. An instantaneous warehouse relative-humidity reading is not the same measurement as the product's water activity. Measurement conditions and product characteristics belong in the assessment. (FDA technical guide)

Deciding that nuts are sufficiently dry should rely on appropriate measurements. The Codex tree-nut code recommends calibrated instruments and representative samples for measurements after drying. This is why we do not give a universal moisture percentage: the meaning of the measurement and acceptance criterion should be defined explicitly for in-shell and shelled nuts. (Codex code)

Protect the result after drying

Rewetting through rain, leaks or condensation makes it harder to preserve the result of drying. FAO's discussion of tree nuts considers moisture, temperature, insects and time together, including leaks and condensation as risk factors. This general mechanism explains why monitoring continues after hazelnuts enter storage. (FAO)

Before storage, assess the following questions:

• Was the product protected from rain during transport?
• Is there a measurement record supporting the drying decision?
• Have damaged nuts and foreign material been separated?
• Can the lot identifier be linked to subsequent records?
• Is there a monitoring plan for evaluating changing storage conditions?

Drying records and aflatoxin results provide different information. They should be assessed together in the same lot file. Our nitrogen storage article discusses maintaining conditions in storage and connecting analytical documents to purchasing decisions. Specifying product form and storage expectations at the outset makes an in-shell hazelnut supply discussion more concrete.

Sources

Hazelnut Research Institute, TAGEM technical guide, Ordu Provincial Directorate, USDA ARS, FDA, Codex, FAO.