The olive may be decidedly trendy today. But most of us have no idea how it is transformed from a hard, bullet-like fruit to the jarred or tinned product that garnishes our cocktails and tops our pizzas.

“It’s a shame that the preparation of olives is such a mystery to most people as it’s not that different to how many people’s grandmas and aunts used to pickle cucumbers and cabbage,” says Nitzan Shatzkin, head grower for Halutza, one of Israel’s most internationally-renowned brands of olives and olive oil.

The reason that few outside the business understand the process is that olive preparation presents a challenge that preserving other crops does not — the olive is totally inedible when picked. It has the same overwhelmingly bitter taste as the chemical added to household products to stop children from drinking them. The effect is identical — it is physically impossible to swallow a raw olive.

“It is in getting rid of the bitterness that the main skill of olive preparation lies,” says Hilla Wenkert, an olive-lover who left the textile business two years ago to set up Olia, which produces olives and olive oil, and runs Israel’s first two olive “boutiques” in Tel Aviv.

Halutza manager Daniel Esses explains that his harvest only works smoothly because the vineyard is organised carefully by breed of tree, which is chosen depending on what they are destined for.

“Before the trees are planted it’s decided, as with grapes in a vineyard, which varieties to use,” he explains. Some breeds, such as the Barnea, are great for making oil but useless as table olives; vice-versa for others such as the Kalamata.

There are no “green breeds” and “black breeds” — different coloured olives come from the same trees. However, the longer they are left, the darker they get. Some olive firms take a short-cut to getting black olives — they dye green ones.

Once olives have been picked, they are placed in vats with holes in them so that they are well ventilated, taken to a processing plant, and run over a series of conveyer belts where leaves are blown off and undersized olives sieved through holes.

Some ways of removing the bitterness are fast and economical, others slow and labour-intensive — and there are no prizes for guessing which are popular in industrial processing.

You can actually often tell by looking at your olive how it lost its bitterness.

Most processing plants take caustic soda, the stuff used to unblock drains, mix it with water, and immerse the olives in it. This quickly draws out the bitter taste from the olive — it works within just 24 hours and therefore keeps factories running efficiently and with minimal labour. But it leads to some of the nutrients being lost and it discolours the olive — a dulled olive is a telltale sign that this method has been employed.

A gentler method involves drawing out the bitterness with water alone (or salt water) but this can take anything up to two months, and the water has to be changed twice a day. When you see olives that are cracked, they will have been processed using this method — the cracking helps the water to circulate.

Sometimes salt alone is used to draw out the moisture from the olives — taking the bitterness with it. This takes around six weeks, and salt must be changed regularly. If you are looking at a dry and wrinkled olive, usually black, often marketed as “Greek style”, this method will have been used.

Salt-treated olives are simply rinsed, sprinkled with a little oil, and packed. If one of the other methods is used, they are rinsed and placed for two months in the solution that will give them their flavour and soften them to make them edible.

This is generally water with 10 per cent salt content and possibly some spices — “you know it’s the right mix when a raw egg floats”, says Wenkert — though sometimes vinegar or wine is used. If they are to be pitted, and perhaps stuffed, this happens as they make their way into jars or tins in a less pungent solution, ready to begin their journey to our tables.