If you drive through the interior of the Algarve in summer you will see, again and again, a tree with a dense dark crown, a twisted trunk and evergreen leaves, planted in stony ground with no irrigation and apparently without care. It is the carob, and it is the most important tree the region has.
Important in a very concrete sense: part of what it produces ends up in the global food industry, and its seed gave its name to the unit used to weigh diamonds.
01 A tree that needs nothing
To understand why this tree is where it is, look at the climate. In the Algarve 455.1 millimetres of rain fall a year, and in July and August, between them, less than half a rainy day. The soil of the barrocal is limestone, stony and shallow.
The carob is one of the few productive species that thrive in those conditions. It has a deep root, leathery leaves that lose little water and a drought tolerance that lets it fruit with no irrigation at all.
That is why it forms a trio with the almond and the fig in the district's traditional farming: three dry-land trees that yield where there is no water for anything else. Of the three, the carob has held up best.
It also has a botanical peculiarity visible at a glance: the flowers and pods sprout directly from the trunk and the old branches, not from the year's new shoots. It is called cauliflory and it is uncommon outside the tropics.
02 Two products in the same fruit
The carob pod is an elongated legume that on ripening turns brown, hard and sweet. And it contains two very different things that go to different markets.
The first is the pulp, which makes up around 90 per cent of the fruit's weight. It is milled and used in confectionery, in syrups and liqueurs, in bread and, in large quantities, as animal feed. It is the part you see in Algarve shops turned into flour, cakes and chocolates.
The second is the seed, which barely weighs a tenth of the fruit and is what rules the value. From its endosperm locust bean gum is extracted, and that is the product that explains why Portugal exports more than half its crop.
The pulp is ninety per cent of the weight and the seed a tenth: almost all the value travels in the tenth.
03 The gum in half your fridge
Locust bean gum appears on labels as E410, and you have probably eaten it this week without knowing. It is a plant-based thickener and stabiliser, very effective cold and with no flavour of its own.
Its most recognisable use is ice cream: it stops large ice crystals forming when the product thaws slightly and refreezes, which is what gives that gritty texture. Hence it is in almost any industrial ice cream.
But the list is long: sauces, fresh cheeses, dairy desserts, baby food, and outside food, cosmetics, pharmacy and the textile industry.
The result is a counterintuitive chain. A tree nobody waters, on stony ground in a dry district, produces an ingredient that travels to factories across half the world, while the visible part of the fruit stays in the district as flour and feed.
04 The carat, and the myth that comes with it
The tree's scientific name is Ceratonia siliqua, and the first word comes from the Greek kerátion, 'little horn', which described the curved shape of the pod. From there, by a direct route, comes the word carat.
The explanation that always accompanies the fact is that carob seeds all weigh almost exactly the same, and that this is why they served as a reference weight for very valuable materials. It is a good story, and it is false.
In 2006 a team tested it by measuring seeds from a collection of carob trees and published the result in Biology Letters. The coefficient of variation in weight was 23 per cent, practically identical to the 25 per cent average of the 63 species reviewed. The carob seed is no more uniform than others.
The same work points to a better explanation. In a perception experiment, observers could tell apart weight differences of around 5 per cent by eye. That is: the seeds used as weights were not naturally equal, they were hand-picked by whoever used them.
05 The state of the groves today
The less cheerful part of the matter is in the forest inventory. Thirty-seven per cent of Portugal's carob is listed in poor health, and that is the highest share among the country's main forest species.
The reasons are cumulative and unspectacular: very old trees with no replacement, plots abandoned when the crop stopped being profitable for decades, and pressure on land in a strip where the alternative is building.
What has changed the picture is price. Industrial demand for the gum revalued the crop, and with it came a new problem: theft of fruit from the fields, which the authorities have had to pursue with seizures measured in tonnes.
06 How to look at it when you are there
The first thing is knowing how to recognise it, which is easy once you know what to look for. A very dense dark crown, leaves made of rounded glossy leaflets, a thick twisted trunk, and pods or flowers coming straight out of the old wood.
The second is the calendar. The flower appears in late summer and autumn; the pod ripens and is collected in summer, usually between August and September, by beating the tree and gathering from the ground. If you go in those weeks, you will see the process under way.
And the third changes what you buy. The carob flour and sweets sold in the district are the part of the fruit that stays here; the part that leaves is invisible and is in your fridge at home. Both are worth trying, even if one of them you can only read as a number.
