Almond

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The almond is a species of tree from the genus Prunus. Along with the peach, it is classified in the subgenus Amygdalus, distinguished from the other subgenera by corrugations on the shell endocarp surrounding the seed.

Its fruit called a drupe, consisting of an outer hull and a hard shell with the seed, which is not a true nut. Shelling almonds refers to removing the shell to reveal the seed. They are sold shelled or unshelled.  Its tree prospers in a moderate Mediterranean climate with cool winter weather. It is rarely found wild in its original setting. 

They were one of the earliest domesticated fruit trees, due to the ability to produce quality offspring entirely from seed, without using suckers and cuttings. Evidence of domesticated almonds in the Early Bronze Age has been found in the archaeological sites of the Middle East, and subsequently across the Mediterranean region and similar arid climates with cool winters. 

Branch of tree with green fruits.

California produces about 80% of the world’s almond supply. Due to high acreage and water demand for almond cultivation, and need for pesticides, California almond production may be unsustainable, especially during the persistent drought and heat from climate change in the 21st century. Droughts in California have caused some producers to leave the industry, leading to lower supply and increased prices.

Description

It is a deciduous tree growing to 3–4.5 metres (10–15 feet) in height, with a trunk of up to 30 centimetres (12 inches) in diameter. The young twigs are green at first, becoming purplish where exposed to sunlight, then grey in their second year. The leaves are 8–13 cm (3–5 in) long, with a serrated margin and a 2.5 cm (1 in) petiole.

The fragrant flowers are white to pale pink, 3–5 cm (1–2 in) diameter with five petals, produced singly or in pairs and appearing before the leaves in early spring. Almond trees thrive in Mediterranean climates with warm, dry summers and mild, wet winters. The optimal temperature for their growth is between 15 and 30 °C (59 and 86 °F) and the tree buds have a chilling requirement of 200 to 700 hours below 7.2 °C (45.0 °F) to break dormancy.

They begin bearing an economic crop in the third year after planting. Trees reach full bearing five to six years after planting. The fruit matures in the autumn, 7–8 months after flowering.

Its fruit is 3.5–6 cm (1+38–2+38 in) long. It is not a nut but a drupe. The outer covering, consisting of an outer exocarp, or skin, and mesocarp, or flesh, fleshy in other members of Prunus such as the plum and cherry, is instead a thick, leathery, grey-green coat (with a downy exterior), called the hull. Inside the hull is a woody endocarp which forms a reticulated, hard shell (like the outside of a peach pit) called the pyrena.

Inside the shell is the edible seed, commonly called a nut. Generally, one seed is present, but occasionally two occur. After the fruit matures, the hull splits and separates from the shell, and an abscission layer forms between the stem and the fruit so that the fruit can fall from the tree. During harvest, mechanized tree shakers are used to expedite fruits falling to the ground for collection.

Gallery

Young almond fruit

Green almonds

Mature almond nut

Almond shell

Stacked from 25 images

A rare double-seeded shell

Stacked from 23 images

Harvested almonds

Blanched almonds

 

 

 

 

 

Taxonomy

Sweet and bitter almonds

                                              

Almond blossom

Blossoming of bitter almond tree

The seeds are predominantly sweet but some individual trees produce seeds that are somewhat more bitter. The genetic basis for bitterness involves a single gene, the bitter flavour furthermore being recessive, both aspects making this trait easier to domesticate. The fruits from Prunus dulcis var. Amara are always bitter, as are the kernels from other species of genus Prunus, such as apricot, peach and cherry (although to a lesser extent).

The bitter almond is slightly broader and shorter than the sweet almond and contains about 50% of the fixed oil that occurs in sweet almonds. It also contains the enzyme emulsin which, in the presence of water, acts on the two soluble glucosides amygdalin and prunasin yielding glucose, cyanide and the essential oil of bitter almonds, which is nearly pure benzaldehyde, the chemical causing the bitter flavour. Bitter almonds may yield 4–9 milligrams of hydrogen cyanide per almond and contain 42 times higher amounts of cyanide than the trace levels found in sweet almonds. 

The origin of cyanide content in bitter almonds is via the enzymatic hydrolysis of amygdalin. P450 monooxygenases are involved in the amygdalin biosynthetic pathway. A point mutation in a bHLH transcription factor prevents transcription of the two cytochrome P450 genes, resulting in the sweet kernel trait.

Origin and distribution

Its precise origin is controversial due to estimates for its emergence across wide geographic regions. Sources indicate that its origins were in Central Asia between Iran, Turkmenistan, Tajikistan, Kurdistan, Afghanistan, and Iraq, or in an eastern Asian sub-region between Mongolia and Uzbekistan. In other assessments, both botanical and archaeological evidence indicates that they originated and were first cultivated in West Asia, particularly in countries of the Levant. Other estimates specified Iran and Anatolia (present day Turkey) as its origin locations, with botanical evidence for Iran as a possible origin centre.

The wild form of domesticated almond also grew in parts of the Levant. Its cultivation was spread by humans centuries ago along the shores of the Mediterranean Sea into northern Africa and southern Europe, and more recently to other world regions, notably California.

Selection of the sweet type from the many bitter types in the wild marked the beginning of its domestication. The wild ancestor of the almond used to breed the domesticated species is unknown. Wild almond species were grown by early farmers, “at first unintentionally in the garbage heaps, and later intentionally in their orchards”.

Cultivation

                                       

Persian miniature depiction of the its harvest at Qand – i Badam, Fergana Valley (16th century)                               

A grove of almond trees An almond shaker before and during a tree’s harvest

They were one of the earliest domesticated fruit trees, due to “the ability of the grower to raise attractive almonds from seed. Thus, in spite of the fact that this plant does not lend itself to propagation from suckers or from cuttings, it could have been domesticated even before the introduction of grafting”. domesticated almonds appear in the Early Bronze Age (3000–2000 BC), such as the archaeological sites of Numeira (Jordan), or possibly earlier. Another well-known archaeological example of the almond is the fruit found in Tutankhamun’s tomb in Egypt (c. 1325 BC), probably imported from the Levant. An article on almond tree cultivation in Spain is brought down in Ibn al-‘Awwam’s 12th-century agricultural work, Book on Agriculture.

Of the European countries that the Royal Botanic Garden Edinburgh reported as cultivating almonds, Germany is the northernmost, though the domesticated form can be found as far north as Iceland.

Varieties

Their trees are small to medium-sized but commercial cultivars can be grafted onto a different root-stock to produce smaller trees. Varieties include:

  • Nonpareil – originates in the 1800s. A large tree that produces large, smooth, thin-shelled almonds with 60–65% edible kernel per nut. Requires pollination from other almond varieties for good nut production.
  • Tuono – originates in Italy. Has thicker, hairier shells with only 32% of edible kernel per nut. The thicker shell gives some protection from pests such as the navel orangeworm. Does not require pollination by other almond varieties.
  • Mariana – used as a rootstock to result in smaller trees

Breeding

Breeding programmes have found the high shell-seal trait.

Pollination

The most widely planted varieties of almond are self-incompatible; hence these trees require pollen from a tree with different genetic characters to produce seeds. Almond orchards therefore must grow mixtures of its varieties. In addition, the pollen is transferred from flower to flower by insects; therefore commercial growers must ensure there are enough insects to perform this task. The large scale of its production in the U.S. creates a significant problem of providing enough pollinating insects.

Additional pollinating insects are therefore brought to the trees. The pollination of California’s almonds is the largest annual managed pollination event in the world, with over 1 million hives (nearly half of all beehives in the US) being brought to the almond orchards each February.

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