It’s hard to avoid olive trees in Spain. As soon as you leave the cities and get into the hills, they are everywhere: any vaguely horizontal patch of land has a tree, almost the only things on the landscape for hundreds of miles. I’m used to seeing apple orchards and corn fields like that, but knew nothing about this particular plant. Time to fix that!
The olive tree, Olea europaea, is an evergreen tree native to the Mediterranean, Asia, and Africa. It is an ancient plant: it’s been cultivated for at least 5000-6000 years, first in Syria, Israel, and Crete. In addition, the trees themselves live for centuries, and some have been shown to live even 2000 years, producing fruit the whole time if they’re well cared for. They’re very vulnerable to cold, but if the tree itself is damaged, the rootstock can survive and produce new shoots, effectively regenerating itself.
Olive trees like hot weather with no shade, and well-drained soil, and they don’t mind dealing with drought. It’s no surprise, then, that Spain is the world’s top producer of olives. Out of the close to 20 million tons of olives produced worldwide, almost 8 million tons are produced in Spain. The next largest producers are Italy, Greece, and Turkey. All this production takes a lot of land: in 2011 9.6 million hectares were planted with olive trees. That’s more than twice the amount of land devoted to apples or bananas; only coconut trees and oil palms take up more space.
Part of the reason olive cultivation takes up so much land is that the trees are traditionally planted very far apart – up to 30 feet away – to allow each tree to get the water it needs. Approximately 40 trees per acre can be planted this way, which means farmers need a lot of land. However, new planting systems are being tested called high-density orchard systems, which can fit between 600-700 trees in an acre. The objective of this new method is to reduce the cost of harvesting the trees, which with traditional methods can be up to half the total production cost.
Olive trees require little in the way of water or other maintenance, except for regular pruning. Proper pruning is essential to keep the trees producing fruit regularly, and to keep the height reasonable for harvesting. Since the branches need to be exposed to light in order to fruit, pruning reduces the density of the foliage, so light can filter through. Finally, olive trees bear fruit on wood grown the year before, which means they tend to produce alternating heavy and light crops. Pruning can help even out the variation in crop sizes.
Pruning is a big deal amongst olive growers – one might think they were talking about the creation of bonsai. For example, one farmer muses:
The production of olive oil is a mystery. Unlike vines where teams of pickers or large machines bring in the vintage, the picking of olives is an inconspicuous operation. Pruning is the same. Vines are transformed from a tangled mass of twigs to neat pared rows of almost identical vines. One rarely sees the olive pruner at work. Perhaps there is a ladder propped against a tree and one sees some prunings on the ground before they are burnt or mulched. It would be a mistake to be fooled into believing that this is a nighttime operation carried out by elves. In fact the classic olive grove is the result of care and attention over many years. The olive trees in Umbria and Tuscany are not by any stretch of the imagination a natural landscape. The untended olive is an untidy bush and it is only through pruning that it has form. Source
Various methods exist to tell you how much to prune. Folklore states that the tree should be open enough for a bird to fly through it, though that isn’t a very precise measurement. On the other hand, apparently scientists have studied this too, and state that the optimal density is such that the leaf area index should be three or four. Leaf area index is the ratio of the area of the leaves on the tree, compared to the area of ground covered by the tree. Again, this isn’t very practical advice, and if you spend all your time counting leaves, you’ll never get your trees pruned. Perhaps it is best to learn from the experts.
Olives are harvested in autumn or winter, depending on the desired end product. Green olives come from fruits harvested early in their ripening period, before they have matured. Black olives are harvested later, after they have matured and the fruit has oxidized and darkened. To harvest the fruit, the boughs of the trees – or the whole tree – can be shaken. However, olives harvested this way result in poor quality oil, and can’t be used as table olives at all, since the fruit is damaged when it hits the ground. Nets can be wrapped around the trunk and opened up to form a catcher for the falling fruit, cushioning it as it lands. Or, in areas where the terrain is too mountainous for machines, the harvest has to be performed by hand, which presumably requires farmers to recruit the entire population of nearby towns to help…
After the fruit is harvested, it has to be processed quickly to prevent it spoiling. Almost all olives are very bitter when fresh, and they have to be cured and fermented before they can be eaten. This process removes oleuropein and other phenolic compounds from the olive and makes them edible (and tasty!). Green olives are first soaked in lye to remove the bitter taste, then washed and lactic acid fermented in brine. Black olives are immediately packed in brine. Some modern methods only use lye to cure the olives, and the process only takes a few days, whereas brine fermentation takes several months. The benefit of the lactic acid fermentation, which uses the natural microflora on the fruit, is that lactic acid is a natural preservative. It lowers the pH of the olives to make the final product more stable against microbe growth and enabling the olives to be stored without refrigeration. Oilves produced by other methods need to be acid-corrected to make them shelf stable.
Making olive oil does not require fermentation: the olives are washed and ground to a paste, with the pits still inside. Next the paste is stirred slowly in a warmed tank, to combine the oil droplets into larger drops. Next, the solids and fruit water are separated from the fruit oil. The traditional method involved squeezing the mass through stacks of grass mats, while modern methods use centrifuges. Finally, the liquid is kept in a settling tank to allow the oil and water to separate, and the oil is bottled. The longevity of the oil depends on the polyphenol (antioxidant) content. The earlier the harvest, the higher the polyphenol content. On the other hand, an early harvest means a lower yield of oil, so there is a tradeoff to be made.
There’s a lot of history behind this delicious fruit (side note: intelligence is knowing an olive is a fruit; wisdom is knowing not to put it in a fruit salad)! It was impossible to avoid olives when we were wandering around Spain – several times we ordered them on accident! I’m happy to know more about where they come from. So: did I miss anything? What else would you like to know about olives? Do tell!
P.S. Fun fact! The Spanish word for olive oil (aceite) came from the Arabic al-zat, or “olive juice”.