Why Are Olives Fermented?

An olive picked straight from the tree looks inviting enough. Bite into one, however, and you are unlikely to do it twice.

Fresh olives are intensely bitter because they contain a naturally occurring compound called oleuropein. Before we can eat them, that bitterness must be softened through curing or fermentation. Done slowly and naturally in brine, the process also develops the olive’s flavour, texture and character.

All our jarred olives, except the feta stuffed olives, are naturally fermented and left unpasteurised. It takes time, but good olives generally do.

In this article

• Why olives cannot usually be eaten from the tree
• How natural olive fermentation works
• How long olives take to ferment
• Whether fermented olives contain live cultures
• The difference between fermented and quickly processed olives
• Whether all Olives Et Al olives are unpasteurised

Why can’t you eat olives straight from the tree?

Olives are stone fruits, or drupes, just like cherries, peaches and plums. Unlike their sweeter relatives, however, olives contain very little sugar and a considerable amount of oleuropein.

Oleuropein forms part of the olive tree’s natural defence system. It helps protect the fruit from pests, but it also gives a freshly picked olive an extraordinarily bitter taste.

There are a few unusual varieties, including the Greek Throuba olive, that lose much of their bitterness as they ripen on the tree. Most olives, however, must be cured before they become pleasant to eat.

What does fermentation do to olives?

Natural fermentation gradually breaks down and removes much of the bitter oleuropein from the fruit.

The olives are submerged in a carefully controlled salt brine. Naturally occurring microorganisms, particularly lactic acid bacteria, begin converting the small amount of sugar within the fruit into lactic acid.

As the acidity increases, the pH of the brine falls. This creates an environment that preserves the olives while allowing their flavour to develop.

The result is something quite different from the raw fruit. The bitterness softens, the texture changes and the olive develops the savoury, fruity and sometimes gently wine like flavours we associate with properly fermented olives.

Rather like bread, cheese or wine, fermentation turns a simple raw ingredient into something altogether more complex.

How long does natural olive fermentation take?

There is no single fermentation time for every olive. The variety, ripeness, size, temperature and strength of the brine all make a difference.

Our green olives are generally fermented for around three to four months. Dark Kalamata olives can take approximately nine months.

That time is not incidental. It is part of making the olive taste as it should.

Once fermented, the olives can be pitted, stuffed or dressed with herbs, spices, citrus and extra virgin olive oil. The fermentation comes first. The recipe comes afterwards.

Do fermented olives contain live cultures?

Naturally fermented olives can carry communities of lactic acid bacteria created during fermentation. These are the live cultures associated with many traditionally fermented foods.

Whether those cultures remain in the finished product depends upon how the olives are subsequently treated. Pasteurisation uses heat to make a product more commercially stable, but the heat also destroys the living microorganisms produced during fermentation.

Because our jarred olives, apart from the feta stuffed olives, are naturally fermented and not pasteurised, their fermentation cultures have not been deliberately destroyed through heat treatment.

Research continues into the particular microorganisms found in fermented olives and their potential benefits. For that reason, we prefer the accurate description naturally fermented with live cultures rather than making sweeping probiotic or medical claims.

Are all olives fermented?

No.

Olives can be prepared in several ways. Some are slowly fermented in brine, while others are treated using faster methods to remove their bitterness. These can include lye treatment, repeated washing, artificial acidification and heat processing.

Some traditional olive styles use lye followed by fermentation, so the use of lye does not automatically mean an olive has not been fermented. What matters is the complete process and whether the finished olives are later pasteurised or sterilised.

Many inexpensive canned olives are processed for speed, uniformity and a very long shelf life. They may still contain fibre, fats and other nutrients, but they will not retain living fermentation cultures after heat treatment.

Natural brine fermentation takes longer and produces greater variation from one harvest to another. We consider that part of the pleasure.

Are Olives Et Al olives naturally fermented?

All our jarred olives, except the feta stuffed olives, are naturally fermented and unpasteurised.

We use cold brining to preserve their freshness or jar them swimming in Extra Virgin Olive Oil to maintain their flavour and texture without using heat to pasteurise them. This applies to our jarred brined, stuffed and flavoured olives, apart from the feta stuffed recipe.

The feta stuffed olives are the exception: they are pasteurised.

To try the slower method for yourself, shop our naturally fermented, cold brined olives. Every olive in our Olives in Extra Virgin Olive Oil range is also naturally fermented and unpasteurised.

Are green olives and black olives fermented differently?

Green and dark olives are not necessarily different varieties. Their colour usually reflects the point at which they were harvested.

Green olives are picked earlier. They tend to be firmer, more bitter and relatively high in polyphenols. They generally need several months in brine before their bitterness softens.

Dark olives are left on the tree for longer. As they ripen, their colour deepens, their texture softens and their oil content increases. Kalamata olives are a familiar example and can require a considerably longer fermentation.

Both can produce excellent table olives. They simply offer different textures and flavours.

Why we choose natural fermentation

There are quicker ways to prepare an olive, but speed is not the only consideration.

Natural fermentation gives the fruit time to lose its harshness gradually and develop the deep, rounded flavour that makes a good olive so satisfying. Leaving the finished olives unpasteurised also means that the cultures created during fermentation are not subsequently removed by heat.

It is a wonderfully simple process: olives, water, salt and time.

Simple, however, should never be mistaken for easy.

Giles Henschel
Founder, Olives Et Al