Dehydration of Walnuts and Pecans

Drying is one of the most important stages in the processing of walnuts and pecans. After harvesting, reducing moisture quickly, uniformly, and in a controlled manner stabilizes the product, preserves its quality, and prepares it for storage, grading, or further processing.

Insufficient drying can lead to preservation problems. But applying higher temperatures or unnecessarily prolonging the process isn't the solution either: the goal is to achieve the correct humidity using controlled airflow and temperature.

Why is it necessary to dry nuts after harvesting?

The fruit of the plant is simply a seed with a germination potential that depends entirely on the temperature and humidity of the fruit. Once the fruit dehisces, and in warm environments, it will begin to lose the organoleptic characteristics typical of a dried fruit if we don't take action. We need to dehydrate the seed to make it edible as quickly as possible.

For reference, industry technical publications place the target moisture content for walnuts at around 8%, while for pecans, values ​​are typically closer to 4.5%. The final value depends on the product, storage conditions, and the commercial requirements of each operation.

Drying does not simply mean applying heat.

One of the most common mistakes is thinking about drying solely in terms of temperature.

In reality, air circulation is a fundamental part of the process.

Air must circulate through the product mass uniformly enough to remove moisture. If there are areas with less airflow, the same load can end up with some sections of fruit that are excessively dry and others that are still too moist.

Therefore, a dehydration system must combine three variables:

• Temperature controlled;
• Adequate air flow and distribution;
• Sufficient exposure time.

Modifying one of them directly affects the others.

Increasing the temperature, for example, can accelerate moisture extraction, but exceeding certain limits can harm fruit quality. The goal of a good system is not simply to dry faster, but to do so homogeneously, consistently, and efficiently.

Check out the following link to find out what happens when we increase the drying air temperature; the result will surprise you:
https://hanutec.ar/blog/secado-de-frutos-1-temperatura-y-tiempo-mas-temperatura-significa-un-mejor-secado

The problem of uneven loads

Not all fruits enter the dryer with exactly the same moisture content. In fact, fruits from the same tree can have several moisture levels that differ.

Harvest time, variety, stage of ripeness, and environmental conditions all contribute to differences within the same batch.

This presents a challenge: if the process is extended to ensure that the fruits with higher moisture content are dry, those that entered drier may end up receiving an unnecessarily prolonged treatment.

In larger-scale operations, controlling the load, product flow, and drying conditions allows for reducing these differences and making better use of both available time and energy.

The importance of a uniform airflow

In an industrial dehydrator, having a heat source is not enough.

The ventilation system must ensure that the air passes correctly through the entire load.

Poor distribution can create preferential air channels: some areas receive a high flow while others are practically isolated.

A properly sized blower and a suitable chamber design allow air to be distributed throughout the product, resulting in more homogeneous drying.

This aspect becomes especially important as the processed volume increases.

Drying 500 kg per batch presents a different challenge than working with several tons simultaneously. With larger volumes, the design of the air circulation system becomes crucial for maintaining consistent conditions throughout the product mass.

Check the following link to find out what happens when we decrease or increase airflow:
https://hanutec.ar/blog/2-flujo-de-aire-por-que-mas-aire-no-siempre-significa-secar-mas-rapido

How to size a drying system?

The capacity of the dehydrator should not be defined solely by the total amount produced during the season.

It is also necessary to consider how much product can be brought in during peak harvest times.

If the intake continually exceeds the drying capacity, a bottleneck is created: the product begins to accumulate precisely at a stage where it is advisable to minimize waiting times.

When sizing an installation, it is advisable to analyze:

• maximum volume received per day;
• usual moisture content of the product upon arrival;
• time available to complete each cycle;
• number of batches that need to be processed separately;
• energy availability;
• capacity of the upstream and downstream stages of the line.

A balanced plant must allow receiving, cleaning, drying, sorting and processing to work in a coordinated manner.

From small producers to industrial plants

Not all operations require the same infrastructure.

For smaller-scale production, working with independent modules and relatively small loads may be sufficient. A larger operation, however, may require several modules or multi-ton drying installations working simultaneously.

Hanutec manufactures dehydrators for walnuts and pecans in different configurations, from 500 kg per load to 20,000 kg systems.

The equipment uses forced air circulation to achieve uniform distribution throughout the product and can be integrated with other stages of a processing line.

Measure before you estimate

Operator experience remains important, but an industrial process should rely less and less on visual estimations.

Measuring the moisture content of the product upon arrival and during the process allows us to truly understand the condition of each batch and determine when to end the drying process.

In addition to improving the consistency of the finished product, this control can prevent unnecessary operating hours and reduce energy consumption.

In larger-scale installations, it is also possible to incorporate automation of temperature control and process monitoring.

Drying as part of a complete line

The dehydrator does not work in isolation.

Its performance depends on how the product arrives and what happens afterward.

A line may include receiving and dosing, cleaning, dehydration, size classification, separation, breaking, and other stages depending on the desired product.

Thinking of these operations as a complete system allows you to detect bottlenecks and size each machine according to the actual production capacity.

At Hanutec we develop equipment and lines for processing walnuts, pecans and other nuts, from product reception to the final processing stages.

If you are planning a new installation or need to increase the drying capacity of an existing plant, we can analyze the production volume and configure a solution tailored to your process.