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Hazelnut roasting and temperature monitoring

Hazelnut roasting is a process that allows hazelnuts to be turned into a must-have ingredient in many recipes.

In this article we will explore the process of roasting hazelnuts, a process that allows this dried fruit to be transformed into a must-have ingredient in many recipes. We will highlight how the quality of the hazelnuts and precision in the roasting process are crucial to achieving an excellent product.

With our case study, we will see how modern environmental monitoring technology supports hazelnut roasting in an industrial setting, offering innovative solutions for this ancient art.


Why do hazelnuts get roasted?

The hazelnut is a very popular fruit (or rather drupe). It has been used for human consumption in Europe since ancient times. It is still highly valued today for its distinctive flavor and crunchy texture.

Hazelnut roasting came about with a primarily practical purpose: to extend the shelf life of the fruit, allowing it to be stored and transported safely. It is in fact a drying process, which reduces the internal moisture of the hazelnuts, thus preventing the growth of mold and bacteria.

Over the centuries, however, roasting has become a method of enhancing the flavor of hazelnuts.

What are roasted hazelnuts used for?

The primary goal of roasting is to obtain a quality, versatile raw material suitable for a wide range of culinary applications.

Roasted hazelnuts can be enjoyed on their own, au naturel or pralined, as nutritious snacks. However, the true value of this product emerges when it is used as an ingredient in confectionery production.

In the world of confectionery, roasted hazelnuts enrich nougat, a dessert popular in many Italian regions especially during the winter period. They are also the key ingredient in desserts such as sbrisolona, a crumbly cake of Lombard origin, and fine pastries such as baci di dama, typical of Cortona.

Chocolate making represents another area of application for roasted hazelnuts. Gianduia of Piedmont is a very sweet cream made from a mixture of cocoa and hazelnuts in varying proportions.

Last but not least, roasted hazelnuts are an essential component in cocoa creams such as the famous Nutella. In these products, hazelnuts not only enrich the taste but also help give the product a spreadable texture that makes them ideal for enjoying on bread or toast.

How to get high quality roasted hazelnuts

To obtain high-quality roasted hazelnuts there are two elements to which special attention should be paid: the variety of hazelnuts and the correctness of roasting.

Of course, the variety of hazelnuts is the essential starting point. Italy is one of the world's leading hazelnut producers and boasts a good range of fine cultivars, each with unique and distinctive characteristics. These include the Tonda Gentile Trilobata IGP from Piedmont, the Giffoni IGP hazelnut from Campania, the Tonda Gentile Romana DOP from Lazio, and the Siciliana or Nostrale from Sicily.

However, even starting with fine raw material, a proper roasting process is necessary to obtain quality roasted hazelnuts. An error at this stage can compromise not only the aroma of the hazelnuts but also their texture.

It is important to carefully monitor the roasting temperature and time. In addition, one must ensure that the hazelnuts are cooked evenly over the entire surface, avoiding scorching in the areas most exposed to heat.

A well-executed roasting process enhances the natural flavor of hazelnuts, releasing an inviting aroma and imparting their characteristic crunchiness.


Methods of roasting hazelnuts

Homemade hazelnut roasting

The roasting process, in its basic fundamentals, is relatively simple, since it does not require specialized equipment. Not surprisingly, many cooking enthusiasts and hobbyist growers make their own roasted hazelnuts.

There are two popular methods:


Toasting in the oven

This process begins by preheating the oven to a temperature around 150-160°C. The hazelnuts should be arranged in a single layer on a baking sheet, untreated. This allows for uniform roasting.

Roasting time varies from 10 to 15 minutes. Meanwhile, the hazelnuts should be checked and turned frequently to prevent burning. Once the desired browning has been reached, the baking sheet should be removed from the oven and allowed to cool to room temperature.


Pan roasting

This technique, ideal for small quantities, requires heating the hazelnuts in a pan over medium-low heat, stirring them with a spoon to ensure even roasting. This method allows more control over the roasting process and usually takes about 5-10 minutes. As with oven roasting, it is critical to allow the hazelnuts to cool to room temperature after roasting.

In either case, roasting is complete when the hazelnuts give off their characteristic aroma, have a darker coloring, and a crisp texture.

Before consumption or use, it is important to remember to remove the brown film that encloses the hazelnut. If the roasting has been done properly, the coating will tend to peel off on its own; therefore, it will be sufficient to shake the hazelnuts or rub them roughly with a cloth to obtain an excellently clean product.


Industrial hazelnut roasting

The basic principles of industrial roasting remain identical to those of home roasting:

  • Exposure to heat for a specific time
  • The continuous movement of the hazelnuts to ensure even roasting
  • The removal of the film

The real difference is that these processes are fully automated and designed to handle large quantities of product.

Roasting is carried out with roasting machines. This equipment is most common in bakeries or semi-craft workshops, which require high quality and a certain production capacity. Depending on the cases and specific needs, general roasting machines can be used, suitable for a wide variety of nuts, or special roasting machines dedicated exclusively to hazelnuts.

Companies that process large volumes of hazelnuts on a daily basis, on the other hand, have large-scale roasting plants.


How to monitor temperature in industrial hazelnut roasting process

An important client operating in the field of confectionery production for large-scale retail trade needed a solution to monitor temperature inside specific vertical ovens, where hazelnuts are dropped from above during the roasting process.

The solution we initially evaluated involved the MicroW S, one of our miniaturized temperature measurement data loggers, equipped with a w cm rigid probe and a 3 mm diameter tip.

The features appeared perfect for the purpose, except that the maximum operating temperature of the data logger was too low for the specific use. In fact, hazelnut roasting ovens can reach temperatures of 160 degrees, while the MicroW S can withstand a maximum of 140 degrees.

To solve this problem, the decision was made to wrap the logger with thermal protection. This solution would have allowed the devices to operate in an environment that exceeds their maximum operating temperature without being damaged, accurately detecting the temperature in the environment where they will operate.

But this was not the only challenge that lay ahead.


New challenges: size and response time

The design and implementation of the temperature monitoring system for the industrial roasting of hazelnuts presented us with two other challenges that we brilliantly overcame:

1.  Specific Dimensions and Custom Thermal Protections

The standard data logger with the thermal protection we had obtained was not compatible with the specifications required by the customer, who needed very small devices.

To solve this problem, our R&D department designed a custom thermal protection that was smaller than the standard, and which met the specified dimensions perfectly.


2. Response Time and Accuracy of Measurements.

Tests conducted revealed that the speed of thermal fluctuations during some stages of the roasting process were extremely rapid, and the standard logger could not track them with due accuracy.

This was crucial because inadequate response times could lead to measurements that were inaccurate or unrepresentative of the actual conditions inside the vertical oven.

As a solution, we switched to a data logger model equipped with a thinner data logger tip: the MicroW L Bendable, featuring a bendable probe only 1.5 mm in diameter.

The thinner tip, by reducing the surface area of the sensor, allowed for much faster response times. In comparison, the 3-mm tip of the Micro W S model, having a larger surface area, took longer to warm up and stabilize at a given temperature. This difference in size, although it may seem small, had a major impact on monitoring. Because of the improved response time, it allowed us to achieve the required precision and accuracy goals.

As a result of our testing, we also ruled out the possibility that the thermal shell, by draining heat, could affect the logger by returning values that were distorted from the actual furnace temperature.


The last challenge

The last challenge concerns the physical protection of the data logger tip, considering the extremely dynamic operating environment in which the device is used.

In the roasting process, the data logger is not only exposed to a cascade of hazelnuts, but also has to endure significant jumps, sometimes up to a meter, between conveyor belts, eventually falling onto a bed of hazelnuts. These conditions present a high risk of damage to the tip, especially considering that it is extremely thin and quite delicate.

To address this challenge, the development of a specific mechanical protection for the tip is underway to protect it from the shocks and mechanical stresses it is subjected to during monitoring.

The protection must be strong enough to absorb shock and prevent damage, but not so bulky as to adversely affect the sensor's response time or its ability to accurately detect temperature changes. This involves careful selection of materials and a design that allows effective protection without compromising the functionality of the device.


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