Syzygium aromaticum

Common name: Clove tree

Names in non-English languages: India Spanish Malaysia

Description

Clove is the dried flower-bud of a tree originating from the Moluccas Islands, a small group of islands in the Indonesian Archipelago in South-East Asia, also believed to be the home of the Nutmeg tree (Myristica fragrans).

Nowadays, clove trees are widely distributed throughout the humid tropics but are most intensively cultivated in Indonesia, India, Sri Lanka, Madagascar and Tanzania. An ancient spice, clove was much valued by the Romans, Greeks and Chinese for its flavouring and medicinal properties.

It is a slow-growing small to medium-sized tree, to heights of up to 20 m (65) in its natural habitat, though in cultivation is more typically 10 to 15 m (32 to 50 ft) tall. The trunk is usually straight and slim, up to 30 cm (1 ft) in diameter, and supports a densely leafy crown. On open sites, young trees develop a pyramidal-shaped crown that becomes cylindrical with age, due to the branches developing a more ascending habit. The bark is grey or pale brown, smooth on young trees, on mature trees rough and cracked.

Leaves elongated oval with a pointed tip, bright pink and soft when they emerge, becoming dark glossy green and prominently ribbed on top, underneath pale dull green and have bright, crimson coloured leaf-stalks. They are arranged opposite along the ends of the branches and remain on the tree in all seasons. When crushed, they have a distinctive clove-like aroma.

Flowers small and insignificant, consisting of pale yellow stamens amidst four tiny petals, atop a tack-shaped flower-bud. The flower-buds are green when young, becoming pink when mature, just before flowering, and are the clove of the spice trade, their colour-change at the pre-flowering stage signalling their readiness for harvest. They arise at the tips of the branches, in clusters of a few or up to fifty or more.

Flowering appears to be influenced by a change from wet to dry conditions, with bud initiation occurring at the end of the rainy season transitioning to the dry season, and with flowering occurring some six months later. In areas having two rainy-to-dry-season events a year, such as Zanzibar, Tanzania, flowering and fruiting follows each event.

The fertilised flowers are replaced by fleshy oblong fruit about 3 cm (1.2 in) in length, green when young, becoming reddish-purple when ripe and with one, occasionally two, small purplish seed inside.

Use

Clove is the unopened flower-bud after it has been thoroughly dried. The buds are harvested when they are at the mature stage, after they have changed colour from green to pink, but not yet started to flower. Drying has traditionally been done under the sun, with the flower-buds laid out on mats or large jute bags and then turned and dried for about a week. After drying, they become dark brown and have lost about 65% of their initial weight.

Dried cloves are widely used around the world, either whole or in powdered form, to impart their unique flavour to both sweet and savoury dishes. In Europe and North America, cloves are added to stews and soups, salty pickling brines to pickle meats such as corned beef, vinegar brines to pickle fish and vegetables, and as well to alcoholic beverages such as warmed mulled wine and beer. In its powdered form, it is commonly used to add spice to fruit pies and tarts,  cakes, sweet biscuits and breads, puddings, various types of sausage meats, as well as sauces such as tomato ketchup.

Other uses of cloves include blending it with tobacco in Indonesia to make a popular local cigarette known as 'Kretek', which may also have other flavours added to it, including extract of Vanilla (Vanilla planifolia) and Coffee (Coffea arabica). Kretek cigarettes are reportedly the preferred type of cigarette for more than 80% of cigarette smokers in Indonesian. Cloves are also used in making alcoholic drinks such as bitters and vermouth, and tea blends such as Chai, the consumption of which is growing rapidly worldwide.

Dried cloves yield on hydro-distillation about 15% of a colourless to pale yellow liquid traded as 'Clove-Bud Oil'. It is a fluid oil with a sweet and spicy clove aroma and a warm, almost burning spicy flavour. It is used extensively as a flavouring agent by the food, beverage and pharmaceutical industries.

Along with other spice-derived essential oils such as Cinnamon (Cinnamomum verum), Clove-bud oil is used for flavouring masticatory products such as chewing gum and chewing tobacco, confectionery, baked goods, and milk and dairy products. Clove-bud oil is also used in perfumery to give perfumes a floral note and is found used in quality perfumes such as 'Fidji' and 'Ysatis'.

The main constituent of clove-bud oil is Eugenol, accounting for around 70 to 90% of the oil by volume. Eugenol, which is also present in commercial quantities in Clove Basil (Ocimum gratissimum) and Allspice (Pimenta dioica), is used mostly in the synthesis of Vanillin, which is what gives Vanilla its characteristic aroma and taste.

Eugenol is also present in the leaves and stems of the clove tree, and on steam distillation, these materials yield 3% and 5% respectively of a colourless to pale yellow oil traded as 'Clove-Leaf Oil' and 'Clove-Stem Oil'. These oils are used mainly as a low-grade substitute for clove-bud oil.

Health use

Clove-bud oil has been demonstrated to have good anti-microbial activity, and with its pleasant aroma and taste has found its way into many toothpaste, mouth-wash and gargle products. Eugenol, the main constituent of the oil also exhibits antioxidant, antibacterial, antiseptic and anti-inflammatory activities. Because of this, clove-bud oil has long been used in the relief of toothache and as a component in dental cement and fillings.

More recently, scientific studies have shown Eugenol to exhibit good antibacterial activity against Salmonella enterica, the bacteria that is a common contaminate of beef, poultry, raw milk and eggs. This holds out promise for Eugenol being used one day as a natural food preservative.

Climate

Grows naturally in humid tropical climates, generally frost-free areas with annual lows of 17 to 25 °C, annual highs of 25 to 35 °C, annual rainfall of 1400 to 4500 mm and a dry season of 3 months or less.

Irrigation can be used to extend Clove cultivation to areas having a dry season lasting up to 5 months. When grown under drier-than-normal conditions, the trees benefit from a micro-climate where irrigation can be misted on them over the top of their canopy.

Clove trees are known to thrive, and to flower and fruit at elevations up to 1000 m (3280 ft) in the Western Ghats mountains of southern India, where the average low of the warmest month does not fall below 18 °C (64 °F).

Growing

New plants can be started from seed, or through vegetative propagation using circumposing (air-layering) and grafting techniques. However, seedlings may vary widely in their characteristics, so vegetative propagation is preferred in commercial operations. The seed take from two to six weeks to germinate and should be sown in a free-draining potting mix and tended in a nursery until they are around twelve months old or 50 cm (1.6 ft) in height.  

Clove trees perform best on rich, free-draining loam, sandy-loam and loamy-sand soils of a moderately acid to neutral nature, generally with a pH of 5.5 to 7.5, and on sites with partial to full sun exposure. However, the young plants need shading for the first few years of life to prevent sun-scorching and it is common practice to plant them under a fast-growing, short-lived perennial such as Banana (Musa acuminata).

Problem features

Clove is recorded as a weed in at least one reference publication but there does not appear to be any record of it anywhere as a serious weed or invasive species.

Where it will grow

With irrigation or groundwater

References

Books

  • Arctander, S. 1960, Perfume and flavor materials of natural origin, Elizabeth, New Jersey

  • Attokaran, M. 2011, Natural food flavors and colorants, Institute of Food Technologists, Wiley-Blackwell Publishing, Oxfordshire

  • Barwick, M., et al. 2004, Tropical & subtropical trees : a worldwide encyclopaedic guide, Thames and Hudson, London

  • Brady, G. S. & Clauser, H. R & Vaccari, J. A. 2002, Materials handbook : an encyclopedia for managers, technical professionals, purchasing and production managers, technicians and supervisors, 15th ed., McGraw-Hill, New York

  • Chevallier, A. 2000, Encyclopedia of herbal medicine, 2nd American ed., Dorling Kindersley, New York

  • Crane, E., Walker, P. & Day, R. 1984, Directory of important world honey sources, International Bee Research Association, London

  • Culbreth, D. M. R. 1927, A manual of materia medica and pharmacology : comprising the organic and inorganic drugs which are or have been recognized by the United States pharmacopœia, 7th ed., Febiger, Philadelphia

  • Debboun, M. & Frances, S. P. & Strickman, D. 2006, Insect repellents : principles, methods, and uses, CRC Press, Boca Raton, Florida

  • Duke, J.A. 1993, CRC Handbook of Alternative Cash Crops, CRC Press, Boca Raton, Florida

  • Fellows, P. 1997, Traditional foods : processing for profit, Intermediate Technology, Technical Centre for Agricultural and Rural Co-operation, London

  • Groom, N. 1997, The new perfume handbook, 2nd ed., Blackie Academic & Professional, London

  • Khan, I. A. & Abourashed, E. A. 2010, Leung's encyclopedia of common natural ingredients : used in food, drugs and cosmetics, 3rd edition, Wiley Publishing, Hoboken, New Jersey

  • Lis-Balchin, Maria 2006, Aromatherapy science : a guide for healthcare professionals, Pharmaceutical Press, London

  • Randall, R. P. 2002, A global compendium of weeds, R.G. and F.J. Richardson Press, Melbourne

  • Randall, R. P. 2007, The introduced flora of Australia and its weed status, Cooperative Research Centre for Australian Weed Management, Glen Osmond, South Australia

  • Stewart, A. 2013, The drunken botanist : the plants that create the world's great drinks, 1st ed., Algonquin Books, Chapel Hill, North Carolina

  • Weiss, E. A 2002, Spice crops, CABI Publishing, Wallingford, United Kingdom

  • Winter, R. 2009, A consumer's dictionary of cosmetic ingredients : complete information about the harmful and desirable ingredients found in cosmetics and cosmeceuticals, 7th ed, Three Rivers Press, New York

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