Corylus Avellana

Hazel is classified in the order Fagales, tribe Corylaceae, genus Corylus. The genus currently includes 25 species among which the most important is Corylus Avellana (common hazel).

It presents the appearance of a large, bushy shrub than a tree, from the number of suckers thrown up by the root. The trunk has smooth and compact bark; the wood is tender and pliant; branches are dotted with numerous lenticels; the cordate, dark green leaves are simple and alternate with serrated margins and pubescence on petiole.

Both vegetative and mixed buds are formed in the axil of the leaves. The terminal position of the mixed buds is characterized by the presence of the dark red hairy styles that emerge from perules in the months from December to February.

The groups of one to five catkins also burst out from the axil of the leaves. They appear in June but are fully developed in the pollen emission period, i.e. from December to February. The fruit of the hazel is a globose-ovoid nucula. Its seed is edible and has a high oil content.
The root architecture exceeds the crown width and grows down in deep, principally in the first 50 cm depending on the nature of the soil and the cultivation techniques.

La "tonda gentile romana"

This hazelnut variety is roughly spherical to oval in shape, with a slightly pointed tip, between 14 and 25 mm in calibre. The shell is of medium thickness, hazel in colour, moderately shiny, with scattered pilosity at the tip and clear striation. The nut is small to medium in size, of a variable subspherical shape, similar in colour to the shell, mostly covered in fibres, with a corrugated surface and quite clear grooves. The perisperm is solid in consistency and crunchy; the flavour and aroma are fine and lingering. Shelled hazelnuts can be consumed raw, dried or roasted. Hazelnuts also come whole, chopped or ground and are suitable for cake, biscuit and ice cream making as well as cream and liqueur preparation.

Ideal soils for hazel groves are loose, fresh, acid and rich in organic substances; the training system depends on the type of cultivation: shrubs, vase-shaped and single-stemmed trees. Pruning takes place each year.Allowed planting density per hectare is 150 for the old trees and 650 for the new seedlings. Average annual production is 4 tons per hectare through irrigation system and 3 tons per hectare through dry farming.

The harvesting of hazelnuts can be done manually or mechanically. Harvesting time is from mid-August to mid-November. Hazelnut crop harvest is followed by storage of the hazelnut crop in suitable premises with good ventilation and with no more than 6% relative humidity. Sorting, grading, treating and conserving must be carried out within one year following the harvest. The yield after shelling is between 28% and 50%.

Hazelnuts are very high in energy and loaded with monounsaturated fatty acids, vitamin E and vitamin K, choline and minerals (potassium, calcium and phosphorus).

In order to understand the importance of hazelnut production for the economy of the Viterbo area, suffice is to say that the agricultural area devoted to cultivation of hazelnuts accounts for over 14% and represents the third more widespread cultivation, after durum wheat (41,4%) and olive (17,4%).

Health benefits of hazelnuts

According to the United States Department of Agriculture “A handful of hazelnuts can do you good!”. Hazelnuts are heart-healthy. Consuming just 1,5 ounces of hazelnuts per day may help reduce the risk of cardiovascular disease.

Hazels are exceptionally rich in folate, which is a unique feature for the nuts. Folate helps prevent neural tube defects in the newborn, coronary artery disease and depression. Hazelnuts have the highest proanthocyanidin content of any tree nut. All these compounds are powerful antioxidants and therefore helpful in improving blood vessel function and in reducing the risk of inflammation and urinary tract infections. Hazelnuts provide dietary fibre. An ounce of raw hazelnuts has 2.7 grams of dietary fibre. Dietary fibre is a cholesterol-lowering nutrient and may prevent constipation because of its laxative effect, according to the 2010 Dietary Guidelines from the U.S. Department of Health and Human Services. Healthy adults on a 2,000-calorie diet should aim for at least 28 grams of dietary fibre.

Hazelnuts are particularly high in two minerals: manganese and copper. One serving of hazelnuts supplies over 25% of the Daily Recommended Intake (DRI) for copper and more than 90% of the DRI for manganese. Copper is needed for iron absorption and manganese is necessary for bone formation.

USDA provides updated data on the nutritional composition of many foods. For specific nutrient profiles for natural, roasted and blanched hazelnuts go to: and sort for keyword “hazelnuts” and food group “nut and seed products”.

Quality parameters

Hazelnuts must meet required standards for the use in confectionery industry. Below is a list of the most important criteria referred to the use and processing of hazelnuts in confectionery:


The spherical shape of the nucula gives a product a more pleasing appearance, ensures a more uniform calibration and shelling. In fact, whole hazelnuts are used in confectionery industry to make pralines, chocolate bars with hazelnuts and baci. Hazelnuts with an elongated shape are less valued and are intended for direct consumption and chopping.


The shelling yield is the ratio between the weight of the kernel and total weight of the fruit. The shelling yield is used as a criterion for a commercial assessment of the product as its price is established per “yield level”. The latter varies from 38% to 50% in case of the most common hazelnut cultivars in Italy.


To prevent hazelnuts from becoming rancid or mouldy, the moisture content should not be higher than 5% to 6%.


The sorting of the shelled product is necessary for separating hazelnuts from foreign substances. To obtain specific calibres, hazelnuts are exposed to the additional calibration. Size classes are as follows:

less than 11 mm
11-13 mm
13-15 mm
over 15 mm.

Only the calibres 11-13 and 13-15 are preferred by confectionery industry since the first class comprehend poorly developed and shriveled kernels. The calibre over 15 mm is intended for direct consumption.


After the roasting process, peeling ability of hazelnut has to be high. Roasting hazelnuts in the oven at 115°C for 30 minutes increases hazelnut aroma and flavor thanks to fat and other compounds breakdown. Once the perisperm (skin that envelops hazelnut kernel) is dry and crumbly, roasted nuts are brushed and the skin is removed from the kernel. Since these integuments have high levels of tannin, it is important to remove them completely. Otherwise, they give hazelnuts bitter and astringent taste and a certain granularity to pastry as the skins are difficult to grind and cannot be homogenized.


The fat content is very variable, ranging from 50% to more than 70%. The average value (62%-65%) give harmonious expression to aroma, perfume and consistency of hazelnut. Higher fat values result in quicker rancidity and product deterioration.

A “panel survey” for hazelnut

A panel survey aims to: identify sensorial profiles of the product varieties covered, , inform consumers, involve producers in product promotion, contribute to quality improvement..

Both dried and medium-roasted hazelnuts are included in the taste test. The assessor engages and reports his senses of sight, smell, taste, touch and hearing while he scrupulously follows the test phases

The sense of sight enables the assessor to evaluate dimensions, sphericity, homogeneity of the calibre, fibrosity and peeling ability of the kernel.
The sense of smell allows to detect aroma’s intensity and descriptors such as aromatic wood fragrances and the scent of the vegetable, bread crust or caramel.
Touch and hearing are used to evaluate texture. Hazelnut crunchiness is associated with the “crunchy” sound generated by their fracture in the oral cavity.
The sense of taste allows to perceive sensations of sweetness, aroma, intensity and aroma persistence.

The test sample consists of at least 6 to 8 hazelnuts and evaluation is made by placing hazelnuts on the white surface.

takes place concerning both unshelled and shelled, i.e. dried or roasted hazelnut.

takes place directly after breaking a dried or a roasted hazelnut so that aroma and intensity can be perceived by olfactory receptors in the nasal cavity.

takes place directly after breaking and chewing dried or roasted hazelnut.

takes place at the moment of breaking a fruit.