Ceratonia siliqua

Common name: Carob

Other common names: Locust Bean, St. Johns Bread

Names in non-English languages: Spanish Portuguese

Description

Carob or Locust Bean is a tree native to the Mediterranean, its natural range extending from Morocco north to Spain and east to Cyprus, Turkey and Syria. A very useful tree, it has long been cultivated for its seedpods, which yield a natural gum used in the food, livestock feed, cosmetic and textile industries.

It is a slow-growing, small to medium-sized tree up to 20 m (65 ft) in height, though is more typically 5 to 10 m (16 to 33 ft) tall and develops a stout trunk supporting a densely leafy, wide-spreading, rounded crown. The bark is dark grey, thin, smooth on young trees becoming flaking with age.

The leaves are 10 to 20 cm (3 to 6 in) long and feather-like, being made up of four to ten oval leaflets arranged in pairs along the length. They emerge bronze-red, become green with a leathery texture and stay on the tree throughout the year.

The flowers are small and insignificant, tubular, petal-less, either female (greenish) or male (tinted red), borne on separate trees, in tail-like clusters arising along the branches. They are followed by straight, sometimes slightly curved seedpods 10 to 30 cm (4 to 12 in) long that hang down from the branches. Green when young, they become dark brown when ripe with five to fifteen very hard seed embedded a sweet, light brown, jelly-like pulp.

Use

The ripened seedpods are rich in sugars and have been used since ancient times as human food and feed for livestock. In more recent times, the seedpods have been transformed into a range of products derived separately from the pod-shells and seed. The de-seeded shells are ground, fermented and distilled into alcohol or are converted into feed cake for cattle. They are also roasted and ground into a flour known as 'carob powder', used as a cocoa or chocolate substitute in baked confectionery and as a colouring and flavouring agent in food.

The seed are the source of 'carob gum', also known as 'locust seed gum', obtained by first grinding the seed to a powder, then dissolving the powder in hot water to produce an adhesive, transparent jelly.

Carob gum has a wide range of applications, particularly in the food, cosmetic, textile and paper industries. Having thickening, gelling, binding, moulding, clouding and flavouring properties. It is used in dairy drinks and desserts, ice cream, fruit drinks, baked goods, salad dressings, mayonnaise, pie fillings, sauces, baby food, soft candy and pet food. It also has application in the textile industry in coating textiles and sizing yarn, as well as in paper manufacturing to improve sheet formation and to increase sheet dry strength. In cosmetics, it is used mostly as a thickener and stabiliser but it is also found used in moisturisers, anti-aging creams, sunscreens, facial masks and nail treatments.

The seed are also ground for feeding to cattle but are high in tannic acid, which is an antifeedant (reduces the digestibility of other feed ingredients) and should not be fed in amounts greater than 20% of the total ration. However, when treated to remove the tannic acid, the meal is highly digestible and has a crude protein content of around 18% of its dry weight.

The flowers produce good quantities of nectar and are foraged by honeybees. The pure honey is dark amber with a subtle, bittersweet flavour reminding of caramel and chocolate and quickly crystallises to a soft, coarse grain.

It produces a medium-weight wood with reddish-brown heartwood that is mostly used for firewood, but which has a tendency to spark, so it is not recommended for open fires.

Health use

Carob powder has long been used as an anti-diarrhoeal in its native range.

Climate

Although naturally adapted to Mediterranean climates, Carob trees flower and produce good quality seedpods in dry to sub-humid subtropical and tropical climates, generally in areas with annual lows of 8 to 22 °C, annual highs of 19 to 35 °C, annual rainfall of 200 to 1400 mm and a dry season of 4 to 10 months. Carob is also cultivated commercially with irrigation in areas where the dry season extends up to 12 months.

Growing

New plants can be raised from seed, but the sex is not easily determined prior to flowering. Common practice, to encourage good pollination, is to graft or bud one or two male branches onto an established female tree.

Performs best on free-draining loam and sand soils of a neutral to alkaline nature, generally with a pH of 7.0 to 8.0 and on sites with full to partial sun exposure. It has good tolerance to limestone soils, but poor tolerance to slow-draining or waterlogged soils.

Yields from mature, rain-fed trees are reported to average 100 to 200 kgs (220 to 440 lbs) of seedpods per year.

Problem features

It is recorded as having naturalised in some countries in the Mediterranean, where it has long been introduced, as well as countries such as Australia, where it is also recorded as having escaped cultivation and a weed of the natural environment. However, there does not appear to be any record of it anywhere as a serious weed.

Where it will grow


References

Books

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  • Webb, D. B. 1984, A Guide to species selection for tropical and sub-tropical plantations, 2nd ed., Unit of Tropical Silviculture, Commonwealth Forestry Institute, University of Oxford, Oxfordshire

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