Nuts and almond kernels - a closer look at nuts and nut trees

The peanut (Arachis hypogaea), also known as the groundnut (US) or monkey nut (UK), belongs to the legume family and does not grow on trees or tree-like shrubs. The peanut plant is an annual herbaceous plant that produces underground fruits known as peanuts (or, more appropriately, “groundnuts”). In comparison with all true nuts, peanuts contain a lower proportion of the vital omega-3 fatty acids. The peanut is native to the Andes in South America, where it has been used since time immemorial. Meanwhile, peanuts are cultivated across large swathes of the subtropics and tropics. The most important peanut-growing areas are North and South America, West Africa, India and China. The five countries USA, Argentina, Sudan, Senegal and Brazil alone account for over 70 per cent of total global peanut exports.

More typical of the Christmas season are hazelnuts, which mostly come from our native hazelnut (Corylus avellana), or from its close relative, the purple hazel (also known as purpurea or purple-leaved filbert (Corylus maxima), which is native to southern Europe. The hazel grows as a multi-stemmed, erect, sometimes tree-like shrub, up to 6 or 8 metres high. The flowers develop into single-seeded nut fruits, popular not only with humans but also a favourite of many animal species, such as squirrels, the hazel dormouse, and nutcrackers. As early as the Stone Age, hazelnuts were appreciated by our ancestors in Europe as an energy-rich source of food. The most important hazelnut-producing countries are Turkey and Italy. The Turkish hazelnut harvest alone accounts for around 70 % of global hazelnut production. The quantities harvested in Turkey are between 400,000 tonnes and almost 800,000 tonnes per year. The hazelnuts themselves contain around 60 % fatty oil and provide around 2,700 kJ of energy per 100 grams of hazelnut kernels. The nuts are used whole or also chopped, in sweets, baked goods, ice cream and chocolate and hazelnut spread.

Another nut typically used in the Christmas season and Christmas baking is the almond. Strictly speaking, however, they are not true nuts in the botanical sense, but the kernels of drupes that merely tend to be known as nuts. The almond tree (Prunus dulcis) belongs to the rose family, and grows as a deciduous, tree-like shrub to heights of 6 to 8 metres, mainly in the Mediterranean region. The almond tree is native to south-west Asia. People have been cultivating almond trees for around 4,000 years. Today, almonds are grown in many countries around the world, including California, Mediterranean countries, Pakistan, Iran, Australia and Turkey. The United States accounts for the largest share of global production, at over 80 %, totalling around 900,000 tonnes. The densely downy drupes are slightly flattened, 3–4 cm long, and have a diameter of 2-3 cm. The seeds, i.e. the almonds themselves, may taste sweet or bitter. There are thus three varieties of almond:

• the sweet almond (Prunus dulcis), Prunus dulcis var. dulcis, with sweet-tasting seeds;
• Prunus dulcis var. fragilis, an almond with a sweet-tasting seed in a thin, brittle kernel shell;
• and the bitter almond (Prunus dulcis var. amara), with bitter-tasting, poisonous seeds.

Almonds are eaten raw, used for decoration in confectionery (almond slivers, almond flakes), and for making marzipan and roasted almonds. In central Europe, the almond ripens only in wine-growing regions, where it was probably introduced together with the vines by the Romans. Almonds contain around 50 % fat.

Just as popular at Christmas time are walnuts, which come from the common walnut (Juglans regia), a deciduous tree from the walnut family. The walnut tree reaches heights of 15 to 25 metres in the open, and up to 30 metres in forest stands. Walnut is a highly sought-after timber for use in the making of high-quality furniture, inlays, veneers and rifle butts. As the walnut tree is sensitive to winter cold and late frosts, it is mainly cultivated in areas with mild winters, such as wine-growing regions. For a long time, botanists assumed that walnuts were a drupe, similar to cherries or plums. Recent morphological studies have now confirmed that the green husk of the walnut is formed from the bracts and bracteoles of the flower shoot. The walnut therefore has a completely lignified pericarp and is in the botanical sense a nut like the hazelnut or the acorn (Aas 2008).

Walnut kernels have a fat content of 42 to 62 %. Of all nuts, walnuts have the highest linoleic acid content, at 7,490 mg/100 g. The energy value of 100 g of walnut kernels is 2,700 kJ. Walnut trees with large crowns may yield up to 150 kg of nuts per tree. Based on a life span of 100 years, an average of 30 kg of nuts per tree can be harvested annually in good locations (Aas 2008). The main walnut-producing countries are China, Iran, the USA, Turkey and Ukraine. Global production has almost doubled in the last 25 years to 1.6 million tonnes. The largest producer is currently China, producing just under 500,000 tonnes, followed by the USA, producing over 300,000 tonnes. In Europe, France produces the largest quantity of walnuts, on a cultivation area of 16,600 hectares, and with a yield of 35,000 tonnes (Aas 2008).

Walnuts are eaten raw, cracked open as whole nuts, or offered as kernels, which are also available commercially. Walnuts also play a role in confectionery, as decoration for desserts.

Also regularly to be found in nut mixtures are Brazil nuts, which come from the Brazil nut tree (Bertholletia excelsa), which can grow up to 50 metres high. This tree species is native to the Amazon region, and the nuts are unusual in that all the Brazil nuts available commercially are nuts gathered from wild trees in the forest. The round fruit of the Brazil nut tree is around 10-12 cm in diameter and contains 10 to 25 seeds - the “Brazil nuts” known to us. This large fruit falls from the tree and remains on the ground in one piece, where it is found by the Brazil nut collectors - or “castaneros”. Alexander von Humboldt was the first European to get to know the Brazil nut tree and described the species during his journey along the River Orinoco.

Each Brazil nut collector has their own collecting area, which can cover from several hundred to up to two thousand hectares, and usually contains a few hundred to a thousand Brazil nut trees. In the tropical rainforest ecosystem, the aguti, a rodent from the guinea pig family, takes on the task of opening the heavily lignified fruits and distributing the seeds within a radius of several to a hundred metres, burying them as a food store. In this way the aguti thus contributes to the spread of the Brazil nut tree. To this day, it has not been possible to cultivate the Brazil nut tree in plantations. A certain species of orchid bee, of the genus Euglossina, is needed to pollinate the fleshy, golf-ball-sized flowers of the Brazil nut tree. This species in turn requires special orchids, which are visited by the male bees solely for their scent, which is attractive to the females. The Brazil nut tree is therefore a good example of how close and diverse the mutual networks of animal and plant species are in the tropical rainforest. The Brazil nuts themselves are 2-5 cm in size and have a high fat content, of up to almost 70 %, and a high proportion of minerals compared to other nuts, especially selenium. For some years now it has however no longer been possible to buy Brazil nuts in their shells in our markets, because the EU has imposed restrictions on the import of Brazil nuts in their shells since 2003. This is because the shells of Brazil nuts may contain the toxin aflatoxin, which can pose a serious health risk. As a result, only shelled Brazil nuts are still available on the market, and the traditional trade in whole Brazil nuts to the EU has declined significantly.

Cashew nuts have become very popular in recent years. The cashew tree (Anacardium occidentale) grows in tropical climates and bears so-called cashew apples, which contain the cashew kernels. The tree grows to a height of 10 to 12 metres and has a diameter at breast height of around 30 cm. The cashew fruit is a small, kidney-shaped structure that hangs from a fleshy, thickened, pepper-shaped fruit stalk. This appendage is also harvested, and the well-known cashew nut is obtained from it. The kernels are sold raw, roasted and salted. They contain around 46 per cent fat per 100 g of cashew nuts. The cashew tree is actually native to Brazil. From there, it was introduced to Mozambique and India by the Portuguese. The largest producer countries today are India, Brazil, Nigeria and Tanzania. In India, cashew nuts only became an important export product and foreign exchange earner from 1970 onwards. The area under cultivation there is estimated to be over 530,000 ha (Trueb 1999).

Another exotic nut species is the macadamia nut, which comes from the macadamia trees (Macadamia integrifolia and Macadamia tetraphylla). Macadamia trees are native to Australia, which is why macadamia nuts are sometimes also called Queensland nuts. Macadamia trees belong to the flowering plant family Proteaceae. Macadamia nuts are considered to be fatty and tasty nuts. They have only become more widely known here in the last ten to twenty years. The Macadamia is also known as the “queen of nuts”. The nuts themselves are round, 1.5-2 cm in diameter, and have a very hard and thick shell, which is why they are almost exclusively sold shelled or processed. The nuts have a high energy content of up to 3,000 kJ and a fat content of over 72 %. It is important for pet owners to know that macadamia nuts are toxic for cats and dogs. In addition to their natural occurrence in Australia, macadamia nuts are also cultivated in Hawaii, New Zealand, South Africa, Israel and California. Hawaii is the largest producer. Many holidaymakers may be familiar with fruiting macadamia bushes or trees from the often beautifully designed grounds of hotel complexes, for example on the Canary Islands or on the Mediterranean coast.

The pecan nut is the fruit of the pecan tree (Carya illinoinensis). The genus Carya includes hickory trees, which belong to the walnut family (Juglandaceae). The pecan nut is native to the south of the USA, where it grows to a height of 30 to 40 metres. The 2.5-5 cm long, egg-shaped fruits are easy to open, and taste similar to walnuts. The pecan tree is the official state tree of the US state of Texas. As well as in the USA, pecan trees are today mainly cultivated in Australia, Brazil, China and Israel. Pecan nuts are highly valued in the USA and used as an ingredient in many dishes and in confectionery. Pecan nut trees thrive in warm conditions and are sensitive to frost. They unfortunately do not (yet) thrive well enough in central Europe for their cultivation to be recommended here.

The fruits of the sweet chestnut tree (Castanea sativa) are edible. They are known in Europe as chestnuts or marroni, and in South Tyrol as “Keschtn”. Sweet chestnuts are large, deciduous trees, closely related to oaks and beeches, which can grow to a great size and age. Their fruits, known as chestnuts or marroni, are shiny, dark brown nuts that sit in groups of one to three in spiny fruit cups called cupules. Compared to other nuts, chestnuts have a very high carbohydrate content, and a very low fat content (around 3 per cent). The sweet chestnut is found around the Mediterranean and is valued there for its edible fruit. In Germany, the main occurrences are on the Upper Rhine Plain, and in the Palatinate, the Odenwald forest and the Lower Main region.

Circular holes in sweet chestnuts or small thick white larvae in the fruit are caused by the chestnut weevil (Curculio elephas), a weevil with a very long proboscis. Its larvae eat the inside of the fruit.

Chestnuts are used in many different ways in the kitchen. In winter, it would be hard to imagine many towns and cities without the stands selling roasted chestnuts. The chestnuts are often roasted over a fire. Other products made from chestnuts include chestnut flour, chestnut purée, chestnut cream and glazed chestnuts.