There is something rather magical about olives.
Perhaps it’s because I love them, but I don’t think I’m alone in finding a bowl of good olives almost impossible to resist.
Green, purple, deep black, wrinkled, plump, stuffed, marinated, briny.
There are so many varieties and so many ways of preparing them that it’s easy to forget something quite extraordinary.
An olive picked straight from the tree is not something you would want to eat.
In fact, it can be intensely bitter.
So how did humans turn this bitter little fruit into one of the most beloved foods of the Mediterranean and Middle East?
The answer is a beautiful combination of observation, patience, preservation and fermentation.
An Olive Is a Fruit
Before we get into what happens to an olive after it is picked, there’s something worth remembering.
Olives are fruit.
They grow on the olive tree, Olea europaea, which has been cultivated around the Mediterranean for thousands of years.
The olive tree is remarkably well suited to Mediterranean conditions. It can tolerate dry climates and relatively poor soils, and its fruit became an important part of traditional food cultures throughout the region.
Olives were not simply something to snack on.
They became part of meals, hospitality, agriculture, trade and daily life.
And of course, the fruit also gave us olive oil.
But the table olive tells a different story.
Why Can’t We Eat Olives Straight From the Tree?
If you’ve never experienced this, you might assume that you could pick a ripe olive, wash it and eat it.
Not so much. The problem is oleuropein.
Oleuropein is a naturally occurring phenolic compound found in olives and is particularly abundant in unprocessed fruit. It contributes significantly to the raw olive’s intense bitterness. And I mean bitter.
The sort of bitter that makes you immediately wonder why anybody ever thought eating an olive was a good idea. But our ancestors didn’t stop there. They found ways to transform the fruit. And that is where the really interesting part begins.
From Harvest to Table
Olives can be harvested at different stages of ripeness. Green olives are harvested earlier. As they mature, their colour changes through shades of green, yellow, purple and eventually black.
The ideal stage depends on the variety and the type of olive being produced. Harvesting itself has traditionally been done in different ways. Olives can be picked by hand, combed from the branches or allowed to fall onto nets placed beneath the trees.
Once harvested, the fruit needs to be sorted and cleaned. Then comes the process that makes the olive edible. Curing.
There Isn’t Just One Way to Cure an Olive
This is one of the things I think is important to understand.
When we say “fermented olives”, we’re actually talking about a variety of traditional processing methods.
Not every cured olive is fermented in the same way.
And some commercial olives aren’t naturally fermented at all.
Water curing
Some olives are treated with repeated changes of water.
The water draws out bitter compounds over time.
This can take considerable patience, and the process may be followed by brining or fermentation depending on the traditional method.
Dry-salt curing
Some ripe olives are cured using dry salt.
The salt draws moisture from the fruit, producing a very different texture and concentrated flavour.
These olives can become beautifully wrinkled and intensely savoury.
Natural brine fermentation
This is the method that is particularly interesting from a fermentation perspective.
The olives are placed directly into a salt brine without first being treated with lye.
Naturally occurring microorganisms then participate in the fermentation.
Lactic acid bacteria and yeasts can play important roles, while salt concentration, temperature, pH and the characteristics of the particular olive all influence what happens.
Natural-style fermentation can take many months.
And this is where traditional food preparation becomes fascinating.
The microorganisms aren’t simply “added”.
They’re already part of the environment surrounding the food.
The process depends on creating conditions in which desirable microorganisms can thrive while less desirable organisms are inhibited.
What Happens During Fermentation?
The raw olive contains sugars and bitter phenolic compounds.
During processing, compounds move between the olive and the brine, while microorganisms transform various components.
In natural fermentation, the microbial activity contributes to acid production and helps change the characteristics of the fruit.
Oleuropein is gradually broken down, reducing the bitterness that makes fresh olives so unpleasant to eat.
The result? A completely different food. Softer, saltier, more complex, and delicious.
What About Lye-Cured Olives?
You may have noticed that I haven’t simply said that all olives are fermented.
That’s because some traditional commercial methods use an alkaline treatment with sodium hydroxide, commonly called lye, to remove bitterness before the olives are placed into brine.
This is known as the Spanish-style method.
The lye breaks down oleuropein and is subsequently washed away before further processing and brining.
It’s a fascinating traditional processing technique, but it’s not the same thing as natural fermentation.
And I wouldn’t recommend experimenting with lye at home unless someone has a very good understanding of the method and the relevant food-safety procedures.
For the purposes of this Spotlight, I’m much more interested in the traditional natural-brine approach.
The Nutritional Story
Now let’s get to the part I think many people will be interested in.
Why are olives such a valued food?
First, olives contain a significant amount of monounsaturated fat, particularly oleic acid.
They also provide vitamin E, fibre and a range of plant compounds, including phenolic compounds such as hydroxytyrosol and tyrosol. The exact nutritional profile varies considerably depending on the olive variety, stage of ripeness and processing method.
And this is where I think it’s important to avoid the modern habit of turning every traditional food into a “superfood”.
Olives don’t need that.
They’re simply a nutrient-dense traditional food that has been enjoyed as part of complete dietary patterns for thousands of years.
The Mediterranean diet is a perfect example.
Olives weren’t traditionally eaten in isolation while somebody ignored everything else they were eating.
They appeared alongside fish, meat, cheese, vegetables, herbs, bread, fruit and other locally available foods.
That whole pattern matters.
What Happens to the Polyphenols?
Here’s where things get particularly interesting.
People sometimes assume that fermentation automatically makes every food more nutritious. It isn’t quite that simple. Processing changes the composition of olives. Some phenolic compounds move into the brine. Others are broken down or transformed. The amount retained in the final olive depends on the variety and processing method.
Research on table olives shows considerable differences between naturally fermented, lye-treated and other commercially processed olives. So rather than saying, “Fermentation increases all the antioxidants”, the more accurate statement is: Fermentation and curing transform the olive’s chemical composition. And some of those transformed compounds are themselves biologically interesting.
That’s much more fascinating than a simplistic health claim.
And What About the Microbiome?
Naturally fermented olives can contain microorganisms associated with the fermentation process, including lactic acid bacteria and yeasts.
But here’s an important distinction. A fermented food isn’t automatically a probiotic food. The microorganisms present depend on how the olives were produced and how they were subsequently processed, packaged and stored.
Some commercially produced olives are pasteurised or otherwise treated after fermentation. So if you’re specifically looking for live cultures, it’s worth knowing how the olives were produced rather than assuming that every jar contains them.
Still, traditional fermented olives have a fascinating place within the broader world of fermented foods. And I think variety is more interesting than chasing one particular “best” fermented food.
Sauerkraut. Kefir. Yoghurt. Kimchi. Kombucha. Water kefir. Beet kvass. Sourdough. And now olives. Different foods. Different microorganisms. Different traditions. Different ways of preparing and enjoying them.
How to Enjoy Olives
Fortunately, this is the easy part.
Olives don’t need much. A good bowl of olives alongside cheese and sourdough can be a meal in itself. You can add them to a salad. Serve them alongside grilled fish. Add them to slow-cooked lamb or chicken.
Mix them into a Middle Eastern mezze. Serve them with eggs. Or simply put a little bowl on the table and let everyone help themselves. And that’s perhaps where olives have always belonged.
At the table. Not hidden away inside a supplement. Not turned into a complicated health product. Simply enjoyed as part of a nourishing meal.
A Food That Connects Us to Place
There is something deeply beautiful about the olive tree.
It grows slowly. It can live for centuries. It survives harsh conditions. And generation after generation of people have harvested its fruit. The methods used to prepare those fruits have travelled through families and communities. Some traditions have changed. Others have remained remarkably similar.
But the basic idea remains: Take something bitter and inedible. Work with nature. Give it time. Transform it. And turn it into something worth sharing.
Perhaps that’s why I find fermented olives such a wonderful addition to this Spotlight series.
They’re not just another fermented food. They’re a little piece of Mediterranean and Middle Eastern history sitting in a bowl on your table. And if you happen to love olives as much as I do, that’s a rather delicious piece of history.
Download the free Microbiome Food Spotlight #9: Fermented Olives for a quick-reference guide to traditional curing, fermentation, serving ideas and microbiome wisdom.
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Disclaimer: The content of this blog post is for informational purposes only and is not intended as medical advice. While I strive to provide accurate, well-researched, and up-to-date information, I am not a licensed medical professional. The insights shared here are based on personal research and experience. I encourage you to conduct your own research and consult a qualified healthcare provider before making any health-related decisions. Your well-being is important, and any actions taken based on the information in this blog are solely at your own discretion and risk.