Almond: Health Benefits, Nutrition & Culinary Guide

• Amygdalus amara Duhamel, 1768
• Amygdalus amygdalina Oken ex M.Roem., 1847
• Amygdalus cochinchinensis Lour., 1790
• Amygdalus communis var. fragilis Ser., 1825
• Amygdalus communis var. macrocarpa Ser., 1825
• Amygdalus decipiens Poit. & Turpin, 1830
• Amygdalus dulcis Mill., 1768
• Amygdalus elata Salisb., 1796
• Amygdalus korshinskyi var. bornmuelleri Browicz, 1974
• Amygdalus sativa Mill., 1768
• Amygdalus sinensis Steud., 1840
• Amygdalus stocksiana Boiss., 1856
• Persica Mill., 1754
• Prunus cochinchinensis (Lour.) Koehne, 1915
• Prunus dulcis (Mill.) D.A.Webb, 1967 nom. superfl.
• Prunus dulcis var. amara (Duhamel) Buchheim, 1972
• Prunus dulcis var. fragilis (Ser.) Buchheim, 1972
• Prunus dulcis var. spontanea (Korsh.) Buchheim, 1972
• Prunus intermedia A.Sav., 1882
• Prunus stocksiana (Boiss.) Brandis, 1906
• Trichocarpus Neck., 1790

The almond (Prunus amygdalus, syn. Prunus dulcis (Mill.) D.A.Webb, nom. illeg. non Prunus dulcis Rouchy) 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 woody shell (endocarp) surrounding the seed.

The fruit of the almond is 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. Almonds are sold shelled or unshelled. Blanched almonds are unshelled almonds that have been treated with hot water to soften the outer skin, which is then removed to reveal the white embryo. Once almonds are cleaned and processed, they can be stored for around a year if kept refrigerated; at higher temperatures they will become rancid more quickly. Almonds are used in many cuisines, often featuring prominently in desserts, such as marzipan.

The almond tree prospers in a moderate Mediterranean climate with cool winter weather. It is rarely found wild in its original setting. Almonds 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 archeological sites of the Middle East, and subsequently across the Mediterranean region and similar arid climates with cool winters.

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

The almond 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.

Almonds 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.

The almond fruit is 3.5–6 cm (1+3⁄8–2+3⁄8 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, mechanised tree shakers are used to expedite fruits falling to the ground for collection.

• Almond blossoms
• Young almond fruit
• Green almonds
• Mature almond nut
• Almond shell
• A rare double-seeded shell
• Harvested almonds
• Blanched almonds

Taxonomy

Scientific name

The almond was named Amygdalus communis by Carl Linnaeus in his Species plantarum in 1753. For the name 'Amygdalus' he referred to Gaspard Bauhin's Pinax (1623). In 1801 the species was for the first time placed in the genus Prunus by August Batsch. In that genus, the name Prunus communis was no longer available because in 1778 William Hudson had already assigned it to a taxon in which he included the plum (Prunus domestica). Batsch thereupon named the species Prunus amygdalus, where 'amygdalus' is the old generic name and should therefore be treated as a noun in apposition. Meanwhile, in 1768, Philip Miller had published the name of what he believed to be a second species of almond: Amygdalus dulcis. He mentioned Linnaeus' Amygdalus communis as the first species. It was not until 1967 that the combination Prunus dulcis was published for the almond by David Allardice Webb, on the assumption that Amygdalus dulcis was nothing more than a synonym of Amygdalus communis, and thus an available name for that species. The epithet dulcis (1768) is older than amygdalus (1801) and would therefore have priority. Webb noted that it was unfortunate that a species known for 165 years as Prunus amygdalus now had to be renamed under the rules of nomenclature. However, it later turned out that in 1967 the name Prunus dulcis was no longer available for the almond because it had already been used for a cherry in an 1878 publication by L'Abbé Rouchy. The oldest valid combination in Prunus is therefore Prunus amygdalus.

Sweet and bitter almonds

The seeds of Prunus amygdalus var. dulcis 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 amygdalus 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 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.

Etymology

The word almond is a loanword from Old French almande or alemande, descended from Late Latin amandula, amindula, modified from Classical Latin amygdala, which is in turn borrowed from Ancient Greek amygdálē (ἀμυγδάλη) (cf. amygdala, an almond-shaped portion of the brain). Late Old English had amygdales 'almonds'.

The adjective amygdaloid (literally 'like an almond, almond-like') is used to describe objects which are roughly almond-shaped, particularly a shape which is part way between a triangle and an ellipse. For example, the amygdala of the brain uses a direct borrowing of the Greek term amygdalē.

Origin and distribution

The precise origin of the almond is controversial due to estimates for its emergence across wide geographic regions. Sources indicate that its origins were in an area stretching across Central Asia, Iran, Turkmenistan, Tajikistan, Kurdistan, Afghanistan, and Iraq, or in an eastern Asian subregion between Mongolia and Uzbekistan. In other assessments, both botanical and archaeological evidence indicates that almonds originated and were first cultivated in West Asia, particularly in countries of the Levant. Most recent sources specified Iran and Anatolia (present day Turkey) as origin locations of the almond, with Iran as the main origin centre.

The wild form of domesticated almond grew in parts of the Levant. Almond 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 almond domestication. The wild ancestor of the almond used to breed the domesticated species is unknown. The species Prunus fenzliana may be the most likely wild ancestor of the almond, in part because it is native to Armenia and western Azerbaijan, where it was apparently domesticated. Wild almond species were grown by early farmers, "at first unintentionally in the garbage heaps, and later intentionally in their orchards".

Cultivation

Almonds were one of the earliest domesticated fruit trees owing to their ability to be grown from seed, allowing their cultivation to have perhaps predated the advent of grafting.

Domesticated almonds appear in the Early Bronze Age (3000–2000 BCE), such as the archaeological sites of Numeira (Jordan), or possibly earlier. They were found in Tutankhamun's tomb in Egypt (c. 1325 BCE), probably imported from the Levant.

Ibn al-'Awwam's 12th-century Book on Agriculture includes an article on almond tree cultivation in Spain.

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

Almond 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 programs have found a high shell-seal trait, which reduces insect damage and mold contamination.

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 almond 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 almond 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 U.S.) being brought to the almond orchards each February.

Much of the supply of bees is managed by pollination brokers, who contract with migratory beekeepers from at least 49 states for the event. This business was heavily affected by colony collapse disorder at the turn of the 21st century, causing a nationwide shortage of honey bees and increasing the price of insect pollination. To partially protect almond growers from these costs, researchers at the Agricultural Research Service, part of the United States Department of Agriculture (USDA), developed self-pollinating almond trees that combine this character with quality characters such as a flavour and yield.

Diseases

Almond trees can be attacked by an array of damaging microbes, fungal pathogens, plant viruses, and bacteria.

Pests

Pavement ants (Tetramorium caespitum), southern fire ants (Solenopsis xyloni), and thief ants (Solenopsis molesta) are seed predators. Bryobia rubrioculus mites are most known for their damage to this crop.

Sustainability

Almond production in California is concentrated mainly in the Central Valley, where the mild climate, rich soil, abundant sunshine and water supply make for ideal growing conditions. Due to the persistent droughts in California in the early 21st century, it became more difficult to raise almonds in a sustainable manner. The issue is complex because of the high amount of water needed to produce almonds: a single almond requires roughly 1.1 US gallons (0.92 imperial gallons; 4.2 litres) of water to grow properly. Regulations related to water supplies are changing so some growers have destroyed their current almond orchards to replace with either younger trees or a different crop such as pistachio that needs less water.

California almond farmers have promoted growing use of sustainable farming practices, including introduction of water-efficient irrigation technology, funding of honeybee health research, and productively using waste biomass (such as shells) in pursuit of a zero waste industry.

Production