Carob tree (Ceratonia siliqua) is a flowering evergreen shrub native to the Middle East and the Mediterranean. Carob tree is often used in ornamental horticulture in gardens and landscaping practices. This shrub has edible pods that are sometimes toasted, ground into powder, and used as a cooking substitute for chocolate. For commercial purposes, the pods are often cultivated in large orchards.
I. Appearance and Characteristics
The carob ( KARR-əb; Ceratonia siliqua) is a flowering evergreen tree or shrub in the Caesalpinioideae sub-family of the legume family, Fabaceae. It is widely cultivated for its edible fruit, which takes the form of seed pods, and as an ornamental tree in gardens and landscapes. The carob tree is native to the Mediterranean region and the Middle East. Portugal is the largest producer of carob, followed by Italy and Morocco.
The carob tree grows up to 15 metres (50 feet) tall. The crown is broad and semispherical, supported by a thick trunk with rough brown bark and sturdy branches. Its leaves are 10 to 20 centimetres (4 to 8 inches) long, alternate, pinnate, and may or may not have a terminal leaflet. It is frost-tolerant to roughly −7 °C (19 °F).
Most carob trees are dioecious and some are hermaphroditic, so strictly male trees do not produce fruit. When the trees blossom in autumn, the flowers are small and numerous, spirally arranged along the inflorescence axis in catkin-like racemes borne on spurs from old wood and even on the trunk (cauliflory); they are pollinated by both wind and insects. The male flowers smell like human semen, an odor that is caused in part by amines.
The fruit is a legume (also known commonly, but less accurately, as a pod), that is elongated, compressed, straight, or curved, and thickened at the sutures. The pods take a full year to develop and ripen. When the sweet, ripe pods eventually fall to the ground, they are eaten by various mammals, such as swine, thereby dispersing the hard inner seed in the excrement.
The seeds of the carob tree contain leucodelphinidin, a colourless flavanol precursor related to leucoanthocyanidins.
II. How to Grow and Care
Sunlight and Soil
Carob tree care dictates establishing the carob tree in an area of the landscape in full sun and well-drained soil. While carob can withstand drought and alkalinity, it does not tolerate acidic soil or overly wet conditions.
Watering
Water the carob infrequently, or not at all, depending on your climate.
Fertilizing
Generally, an established plant will not need to be fertilized, but if these problems are plaguing the tree, a dose of fertilizer may be beneficial and, of course, cut back on irrigation.
Planting Instructions
Sowing seed directly is probably the most common method for how to grow carob trees. Fresh seeds germinate quickly, while dried seeds need to be scarred and then soaked for a period of time until swollen two to three times in size. Traditionally planted in flats and then transplanted once the seedlings attain a second set of leaves, germination for carob trees is only about 25 percent certain. Carob should be spaced 9 inches (23 cm.) apart in the garden. For the home gardener, an established 1-gallon (4 L.) carob tree start might more prudently be purchased from a nursery.
Keep in mind that conditions in your garden must closely mimic those of the Mediterranean or grow carob in a greenhouse or in a container, which can be moved into a protected area indoors. Carob trees may be grown in USDA zones 9 through 11. Be patient as carob trees grow slowly at first but begin to bear in the sixth year of planting and may remain productive for 80 to 100 years.
Pests and Diseases
Few pests are known to cause severe damage in carob orchards, so they have traditionally not been treated with pesticides. Some generalist pests such as the larvae of the leopard moth (Zeuzera pyrina L.), the dried fruit moth (Cadra calidella), small rodents such as rats (Rattus spp.) and gophers (Pitymys spp.) can cause damage occasionally in some regions. Only some cultivars are severely susceptible to mildew disease (Oidium ceratoniae C.). One pest directly associated with carob is the larva of the carob moth (Myelois ceratoniae Z.), which can cause extensive postharvest damage.
Cadra calidella attack carob crops before harvest and infest products in stores. This moth, prevalent in Cyprus, will often infest the country’s carob stores. Research has been conducted to understand the physiology of the moth, in order to gain insight on how to monitor moth reproduction and lower their survival rates, such as through temperature control, pheromone traps, or parasitoid traps.
III. Uses and Benefits
- Food
Carob products consumed by humans come from the dried, sometimes roasted, pod, which has two main parts: the pulp accounts for 90% and the seeds 10% by weight. Carob pulp is sold either as flour or “chunks”. The flour of the carob embryo (seed) can also be used for human and animal nutrition, but the seed is often separated before making carob powder (see section on locust bean gum below).
Carob pods are mildly sweet on their own (being roughly one third to one half sugar by dry weight), so they are used in powdered, chip or syrup form as an ingredient in cakes and cookies, sometimes as a substitute for chocolate in recipes because of the color, texture, and taste of carob. In Malta, a traditional sweet called karamelli tal-harrub and eaten during the Christian holidays of Lent and Good Friday is made from carob pods. Dried carob fruit is traditionally eaten on the Jewish holiday of Tu Bishvat.
Carob powder
Carob powder (carob pulp flour) is made of roasted, then finely ground, carob pod pulp.
Locust bean gum
Locust bean gum is produced from the endosperm, which accounts for 42–46% of the carob seed, and is rich in galactomannans (88% of endosperm dry mass). Galactomannans are hydrophilic and swell in water. If galactomannans are mixed with other gelling substances, such as carrageenan, they can be used to effectively thicken the liquid part of food. This is used extensively in canned food for animals in order to get the “jellied” texture.
Animal feed
While chocolate contains the chemical compound theobromine in levels that are toxic to some mammals, carob contains none, and it also has no caffeine, so it is sometimes used to make chocolate-like treats for dogs. Carob pod meal is also used as an energy-rich feed for livestock, particularly for ruminants, though its high tannin content may limit this use.
Historically, carob pods were mainly used for animal fodder in the Maltese islands, apart from times of famine or war, when they formed part of the diet of many Maltese people. On the Iberian Peninsula, carob pods were historically fed to donkeys.
Maltese carob liqueur
The pulp of a carob pod is about 48–56% sugars and 18% cellulose and hemicellulose. Some differences in sugar (sucrose) content are seen between wild and cultivated carob trees: ~531 g/kg dry weight in cultivated varieties and ~437 g/kg in wild varieties. Fructose and glucose levels do not differ between cultivated and wild carob. The embryo (20-25% of seed weight) is rich in proteins (50%). The testa, or seed coat (30–33% of seed weight), contains cellulose, lignins, and tannins.
- Syrup and drinks
Carob pods are about 1/3 to 1/2 sugar by weight, and this sugar can be extracted into a syrup. In Malta, a carob syrup (ġulepp tal-ħarrub) is made out of the pods. Carob syrup is also used in Crete, and Cyprus exports it.
In Palestine, crushed pods are heated to caramelize their sugar, then water is added and boiled for some time. The result is a cold beverage, also called kharrub, which is sold by juice shops and street vendors, especially in summer.
In Lebanon the molasse is called debs el kharrub (literally: molasse of the carob), but people generally shorten it to debs. The molasse has a sweet, chocolate-like flavor. It is commonly mixed with tahini (typically 75% kharrub molasses and 25% tahini). The resulting mixture is called debs bi tahini and is eaten raw or with bread. The molasse is also used in certain cakes. The region of Iqlim al-Kharrub, which translates to the region of the carob, produces a significant amount of carob.
In Cyprus, the dried and milled carob pods are left to soak in water, before being transferred into special containers out of which the carob juice gradually seeps out of and is collected. The juice is then boiled with constant stirring yielding a thick syrup known as haroupomelo. Although this syrup is frequently sold and eaten as is, haroupomelo is also used as a base for a local toffee-like sweet snack known as pasteli. Constant stirring of the carob syrup causes it to form into a black, amorphous mass which is then left to cool. The mass is then kneaded, stretched and pulled until the fair, golden color and toffee-like texture of pasteli is obtained.
Carob is used for compote, liqueur, and syrup in Turkey, Malta, Portugal, Spain, and Sicily. In Libya, carob syrup (called rub) is used as a complement to asida (made from wheat flour). The so-called “carob syrup” made in Peru is actually from the fruit of the Prosopis nigra tree. Because of its strong taste, carob syrup is sometimes flavored with orange or chocolate. In Yemen, carob tree is playing a role in controlling diabetes mellitus according to Yemeni folk medicine, and diabetics consume carob pods as a juice to lower their blood sugar levels.
- Ornamental
The carob tree is widely cultivated in the horticultural nursery industry as an ornamental plant for Mediterranean climates and other temperate regions around the world, being especially popular in California and Hawaii. The plant develops a sculpted trunk and the form of an ornamental tree after being “limbed up” as it matures, otherwise it is used as a dense and large screening hedge. The plant is very drought tolerant as long as one does not care about the size of the fruit harvest, so can be used in xeriscape landscape design for gardens, parks, and public municipal and commercial landscapes.
- Timber
In some areas of Greece, viz. Crete, carob wood is often used as a firewood. As it makes such excellent fuel, it is sometimes even preferred over oak or olive wood.
Because the much fluted stem usually shows heart rot, carob wood is rarely used for construction timber. However, it is sometimes sought for ornamental work–particularly for furniture design, as the natural shape of the trunk is well-suited to the task. Additionally, the extremely wavy grain of the wood gives carob wood exceptional resistance to splitting; thus, sections of Carob bole are suitable for chopping blocks for splitting wood.
IV. Harvesting and Storage
The most labour-intensive part of carob cultivation is harvesting, which is often done by knocking the fruit down with a long stick and gathering them together with the help of laid-out nets. This is a delicate task because the trees are flowering at the same time and care has to be taken not to damage the flowers and the next year’s crop. The literature recommends research to get the fruit to ripen more uniformly or also for cultivars which can be mechanically harvested (by shaking).
After harvest, carob pods have a moisture content of 10–20% and should be dried down to a moisture content of 8% so the pods do not rot. Further processing separates the kernels (seeds) from the pulp. This process is called kibbling and results in seeds and pieces of carob pods (kibbles). Processing of the pulp includes grinding for animal feed production or roasting and milling for human food industry. The seeds have to be peeled which happens with acid or through roasting. Then the endosperm and the embryo are separated for different uses.
