Olea europaea



The eastern Mediterranean area between Turkey and Syria. Evidence of human use dates back to 9000BC.


The olive grows well in a Mediterranean-type climate such as Perth, with cool winters and long hot dry summers. Worldwide cultivation is mainly within latitudes 30-45 degrees at less than 900m elevation.  All varieties need sufficient winter chilling (<7°C) to induce flowering, but heavy frosts/freezes (-10°C) will kill trees.  Optimum temperatures for shoot growth and flowering are 18-22°C.  Water requirements are 500-800mm pa during the critical growth periods.

They are not adapted to humid climates.

Plant Description

It is a hardy long-lived shrub or small tree, 4-8m high.  The evergreen leaves which persist for 2-3 years are simple rigid entire decussate lanceolate-elliptic with smooth margins, 3-9 X 1-2cm, and well-adapted to xerophytic climates. Upper and lower surfaces are dark green and silvery-grey respectively.  Depth and spread of the root system with cutting-grown plants depends on soil, moisture and aeration.


Oleaceae Family. Olea europaea is divided into 6 subspecies so that the cultivated olive has the complete botanical designation  O. europaea subsp. europaea var. europaea.  The olive is the only species in the family cultivated for its fruit.


Undemanding if they’re well-drained, including alkaline soils (pH up to 8.5).  Overly fertile soils favour vegetative growth rather than flowering.


Most varieties are propagated by taking 30-40 cm cuttings from one-year-old wood, with better results from material towards the base of the tree.  There are roughly equal proportions of cultivars with high, medium or low rooting ability.

Kalamata is one that is routinely grafted as cuttings are difficult.  Seedlings should only be used as a source of rootstocks.


There are over 1000 varieties worldwide, but many of these are just different names in different regions.  Particular cvs usually are better for oil production or pickling, but some are dual purpose.  Table varieties are usually larger than those for oil.  Manzanilla, Kalamata and Mission/New Norcia are some which can be used either way.  Others that can be easily sourced in WA are Verdale, Sevillano, UC13A6 and Barouni. Care should be taken in selection of varieties that cross-pollination and chill hour requirements are met; regularity of bearing and flesh/seed ratio are also important considerations.

Flowering and Pollination

Paniculate inflorescences that form in leaf axils of 1-year-old wood contain 10-40 small flowers in groups of 3-5.  Olives are andromonoecious.  In staminate flowers the pistil is absent or non-functional and the proportion of these is governed by cultivar and environment, reaching 50% in adverse conditions.  In hermaphrodite flowers there is a green persistent calyx, 4 white yellowish-white petals, 2 stamens and a single pistil with a 2-lobed stigma and superior ovary containing 2 locules that each have 2 ovules.  Flowering occurs in spring after winter chill hours have been met, remaining receptive for 3-4 days.  Fruit set may be 5% through wind pollination but occasionally also by insects.  Only one of the 4 ovules is typically fertilized.  Olives can be self-fertile, partially self-fertile or self-infertile, so cross-pollination becomes an important issue with some cvs.


They should be planted in full sun.  Although mature trees will survive through lengthy drought periods, yield will be reduced without appropriate watering.  The trees are not nutrient hungry, but yields increase with a balanced fertilizer program where the main application is given in April followed by smaller amounts in September and January.

Wind Tolerance

Olives are reasonably tolerant to wind and storms.


Training the young plant to form a vase system will limit height, maximise light penetration, minimise disease load, and increase aeration and ease of hand harvesting.  Most olive cvs have a tendency to alternate bearing, but pruning in heavy (‘on’) years can reduce this somewhat. Fruit is borne on one-year-old wood.

The Fruit

This drupaceous fruit is round-ellipsoid, 1-4 X 0.5-2cm, green throughout development and turns dark purple or black at maturity. The edible flesh has 20-30% oil, 3-6% sugars, 2-6 % fibre and good levels of Ca and Fe.  Most of the oil is the healthy monounsaturated type.  There is a single hard stone (pit).

Fruit Production and Harvesting

Juvenility for seedlings can last 10 years, 4-6 for those vegetatively propagated.  Fruit mature over 6-7 months following fertilization.  Table olives are then hand-picked from late February to July in Perth when they’re mature green, at colour change or black depending on variety, desired pickling style and product. Kalamata are picked black.

Fruit Uses

Worldwide commercial production of olives is predominantly for oil production (>90%).  In Perth home gardens, table (pickling) varieties are mainly used for culinary purposes but must first be debittered. This normally involves soaking in a 10% salt solution for a few months; a faster process is to use a lye solution.  Usually, black olives are less bitter than green and need less processing to become edible.  Green or black fruit can be stored in the same salt solution for many years if desired, which is a positive feature given olives are frequently irregular bearers. A few weeks before use, thoroughly rinse out the brine solution from fruit and place into olive oil, plus herbs and spices, if desired.

Pests and Diseases

The major pests are scale insects such as black scale and olive scale. The olive lace bug is a new pest. Parrots may cause some damage.


Commercial orchards range from Geraldton to Albany, with the main area in Gingin. Olives grow and fruit well in Perth home gardens; they are also hardy ornamentals and can serve as a good windbreak.   Well-managed mature trees can produce thousands of fruit per year, 40-50 kg in good years.  Alternate bearing behaviour may mean irregular yearly cropping. A commercial proprietary firm in Perth will process for oil, but needs a minimum of about 50kg fruit. Olives can be de-bittered by drying.

More Information

De-bittering olives by drying – a fast & healthy technique

Very few olives can be eaten straight off the tree because of the presence of the bitter phenolic glucoside oleuropein in the flesh. This has to be degraded to produce edible fruit. Traditional approaches have been to use salt or lye (sodium hydroxide) solutions. This has the disadvantage of possibly adding significant levels of sodium to the diet in a culture where most people are already consuming much more than required and recommended by the Australian National Medical Research Council, the Heart Foundation and other similar bodies worldwide. Consumers can attempt to rinse out this sodium before use, or another alternative is to use the very much slower de-bittering technique of repeatedly soaking and rinsing in water.

The present approach avoids these issues solely through application of heat, with progressive drying of the fruit until the bitter flavour is no longer present. Generally the larger the fruit the better the return in terms of edible flesh compared to the pip; this consideration is less important when the intent is to produce oil. There is usually a successive decrease in bitterness as fruit progress from mature green to turning colour to fully ripe black on the tree, so it’s the latter that are preferred as they’re easier and quicker to process. The goal is to ensure the bitterness is suitably reduced with minimal heat/duration exposure by periodic sampling. Fruit can be dried to the texture level preferred, ie chewy, flexible or with more drying time, crisp and breakable. Most people prefer to stop well before the crisp stage, but at these earlier times there will be more moisture remaining in the flesh and this reduces storage life. So you can decide on a ‘sweet spot’ that balances your palate preference with how long you’d like to keep a batch before mould growth will develop.


  1. After picking, wash the fruit and remove any non-fruit material such as twigs and leaves.
  2. Olive fruits have a thick waxy cuticle on the skin that helps minimize the chances of desiccation while developing  on the tree. Fruit can be dried with this layer intact, but the rate of loss of moisture in the drying process will be  slower. If the cuticle is cut or compromised by 30 seconds of blanching, the drying proceeds faster. Unless you have  a special pitting machine, there is no need to remove the pit as typically a home-grower might collect buckets full of  fruit at harvest and pitting one by one with the simple hand-operated devices available would take forever.  Similarly, cutting individual fruits one at a time with a knife is very slow. One way to speed up cutting the cuticle  is by using a common kitchen vegetable chopper. Normal use of these is to place pieces of veges under the rim and  then by pushing down a plunger connected to a zig-zag series of cutters you can manually chop up the material very  quickly. Same approach with olives – put several at a time under the rim, a couple of pushes and presto, you have  cuts randomly made throughout the fruits. Several kilos of fruit can be done quickly By severing the flesh you  finish up with a more appealing product that hasn’t bee universally flattened, such as occurs traditionally in some  societies if you just squash the fruit using (say) the bottom of an empty bottle. You obtain even less obvious fruit  disruption with blanching. Most people decide not to to bother with any of this & simply dry fruits whole.
  3. The cleaned fruit are spread out, single-layered, on the tray of a dehydrator and heated at 60°C for sufficient  time to enable the de-bittering. Unfortunately, many dryers available at the retail level don’t allow precise  temperature control – there might be just 1-3 levels. If you have one of these types you’ll have to experiment to find  the best setting. Plus the air flow is often from one tray to the next, so moisture is not directly vented but flows over  other fruit, slowing down drying. Horizontal air flow where vapour from each tray is directly vented is preferred.
  4. Taste periodically to finesse your run time, minimising heat exposure. With an efficient dehydrator & fully ripe olives, you can de-bitter in <24hrs – all done.
  5. If product is not dried to very low levels, you can store for longer under olive oil but this is adding to a product that  has already had its own oil content enhanced through drying, and adds to cost & total calories. Storing in brine goes  back to the original concern of sodium, sodium everywhere in Western diets. The best strategy is to pickle – this  allows fruit to be stored at ambient temperature for several months, especially if double strength vinegar is used.
  6. After drying, spices can be added & mixed through if you wish to add to flavour. Wash out the vinegar thoroughly  before consumption.
Olives and olive oil – how good are they nutritionally?

The olive tree (Olea europaea) has been grown from ancient times for its fruits. It’s a very hardy species that thrives in a Mediterranean climate and consequently was extensively incorporated into the national cuisines of southern European countries. In more recent times it has gained a valued reputation as one of the important components of the healthy Mediterranean Diet (MD) that has been demonstrably effective in reducing the incidence of chronic diseases so prevalent throughout developed countries and increasingly elsewhere. Most fruit production worldwide (about 90%) is used to make olive oil for garnishing and cooking. High consumption is the norm in southern European countries. For example, in Greece, adults consume an average of 80g/d and in Spain, as a result of high olive oil intake, fats may represent over 40% of dietary calories. The following commentary is focussed only on the nutritional aspects of plant-based oils; their comparative organoleptic properties are quite subjective and strongly dependent on historical and national traditions and will not be considered here.

Although established as a revered and proven component of the MD, are there other plant-based oils that are equally beneficial for long term well-being or maybe even better? Does the attention given to distinctions between various virgin oils and other cheaper refined oils have any nutritional basis? Or is it more a case of olive oil users supporting what is a long-cherished culinary tradition in the Mediterranean basin based on availability in earlier times when globalised sourcing of foods was less feasible and there was little scientific knowledge comparing the relative merits of others?

Healthy diets recommended by world authorities should have 20-35% of total daily calories contributed by fats. It’s common knowledge that not all fats are equal. Trans fats should be avoided altogether or at least kept below 1%, and saturated fats which predominate in animal-based foods should be restricted to less than 7% of energy intake. The value of plant-based fats is that they have low saturated fats (apart from palm and coconut) and consist mainly of mono- and poly-unsaturated fatty acids (MUFA and PUFA respectively). Only two fat types are essential for humans – the polyunsaturated omega-6 and omega-3 oils (n-6 and n-3 resp) as we can synthesize all the rest from other nutrients. The problem in Western diets is to ensure sufficient n-3 intake to avoid deficiency symptoms and also contribute to long-term well-being, with 1-3 g/d commonly recommended (of which 10% can be the long chain n-3 marine oil types) as n-6 consumption is usually far in excess of needs; the preferable limit for these is less than 10% energy intake. Total fat intake in a healthy diet should be more than the 3g/d contributed by essential fats to enable, for example, absorption of fat-soluble vitamins and other phytonutrients from the gut food matrix. For many years it was thought that the main contribution of olive oil to the MD was the high concentration of MUFA (73%), principally as oleic acid. But more recently it has been found that non-fatty acid phytochemicals (polyphenols/ antioxidants) also have an important role, maybe even the dominant one. This is a nutritional basis for distinguishing between virgin and more refined olive oils as the former have much higher antioxidant levels than the latter.

Oils with high levels of PUFA including the n-6 and n-3 fatty acids are much more prone to degradation/oxidation (rancidity) than MUFA. Given the main use of olive oil is in producing cooked foods, it has the relative advantage with high MUFA of increased thermal stability but the disadvantage of low PUFA, meaning it is low in essential oils (9.8% n-6 and 0.8% n-3). Canola oil is an alternative to olive oil (19% n-6 and 9.1% n-3). Although it only became available in1979 following successful Canadian research and consequently has not benefited from the many centuries of use that olive oil has enjoyed in Europe, it currently far exceeds it in world production and consumption. Epidemiological and clinical trial evidence for its positive effects in humans versus onset of chronic diseases is as impressive as olive oil. At a more basic level it has roughly equivalent MUFA content (63% vs 73%) conferring cooking stability, but more importantly a much better content and balance of the n-3 essential fatty acids. The following paper (Exp Biol Med (2008) 233:674–688) makes the case for lowering the ratio of omega-6/omega-3 oils in Western diets.

Several sources of information suggest that human beings evolved on a diet with a ratio of omega-6 to omega-3 essential fatty acids (EFA) of about 1 whereas in Western diets the ratio is 15/1– 16.7/1. Western diets are deficient in omega-3 fatty acids and have excessive amounts of omega-6 fatty acids compared with the diet on which human beings evolved and their genetic patterns were established. Excessive amounts of omega-6 polyunsaturated fatty acids (PUFA) and a very high omega-6/omega-3 ratio, as is found in today’s Western diets, promote the pathogenesis of many diseases, including cardiovascular disease, cancer, and inflammatory and autoimmune diseases, whereas increased levels of omega-3 PUFA (a lower omega-6/omega-3 ratio) exert suppressive effects. In the secondary prevention of cardiovascular disease, a ratio of 4/1 was associated with a 70% decrease in total mortality. A ratio of 2.5/1 reduced rectal cell proliferation in patients with colorectal cancer, whereas a ratio of 4/1 with the same amount of omega-3 PUFA had no effect. The lower omega-6/ omega-3 ratio in women with breast cancer was associated with decreased risk. A ratio of 2–3/1 suppressed inflammation in patients with rheumatoid arthritis, and a ratio of 5/1 had beneficial effect on patients with asthma, whereas a ratio of 10/1 had adverse consequences. These studies indicate that the optimal ratio may vary with the disease under consideration. This is consistent with the fact that chronic diseases are multi-genic and multi-factorial. Therefore, it is quite possible that the therapeutic dose of omega-3 fatty acids will depend on the degree of severity of disease resulting from the genetic predisposition. A lower ratio of omega-6/omega-3 fatty acids is more desirable in reducing the risk of many of the chronic diseases of high prevalence in Western societies, as well as in the developing countries.

The n-6/n-3 ratio for olive oil is about 12.2/1 and for normal canola it is 2.1/1 with enhanced n-3 forms having an even lower ratio. With comparable impressive evidence for their health conferring properties over animal-based fats, it may thus be possible to achieve further improvements in the MD by substituting canola oil for olive oil. Additional considerations are that canola has approximately half the saturated fat content as olive oil (7.4 vs 14%) and it’s cheaper than the various speciality virgin olive oils. But realistically, traditional customs are very resistant to change.

So if individuals choose to keep olive oil as a part of the MD it is important to realise that the whole fruit, de-bittered by the Spanish brining technique, has the same oil with more healthy fibre, lower calories with 50% contained water, and for black olives, about 20 times (!) the antioxidant level as extra virgin olive oil. Such a large difference in nutrient content between different parts of a food (eg after peeling, de-seeding, juicing or oil expression) is unusual but some differences are the norm and should always be considered when deciding on the nutritional merit of a given processing technique.

Two obvious factors contributing to such a disparate outcome in this instance are that water soluble nutrients will not be included in separated oil, and other phytonutrients that are extensively membrane-bound will also be left behind with oil expression. So committed MD olive oil consumers might expect enhanced health outcomes by substituting or supplementing part of their oil intake with table olives. If olive oil was to be the sole source of n-6/n-3 fatty acids in the diet, then for men, they would have to consume about 210g /d to meet recommended n-3 levels versus 16g/d for canola which also provides a superior n-6/n-3 ratio.

Both olive and canola oils are valuable foods, but when used at elevated temperatures for frying, they are nevertheless still subject to finite chemical degradation to a number of unhealthy substances that occur more extensively above 150°C. This is why food outlets such as fish and chip shops have to totally replace their oil periodically (apart from straining out particulates) when deterioration has progressed beyond certain levels. Production of these substances is minimal when the oil is used only once for cooking a given meal, provided the temperature/time is not excessive.

However with the higher temperatures/rapid cooking used in popular Asian stir frying techniques (oil taken to the smoke point and beyond) more dangerous carcinogens are formed, some volatile. As a result, a several-fold higher incidence of lung cancer is seen in cooks frequently using this technique, especially where there may be poor or ineffective ventilation. Also, with higher temperature/cooking frying time combinations, the degradation of valuable phytochemicals can be profound. This may be made even worse when water-based boiling follows the frying.