Olives are too bitter to be eaten right off the tree and must be cured to reduce their intrinsic bitterness. Processing methods vary with the olive variety, region where they are cultivated, and the desired taste, texture and color. Some olives are picked unripe, while others are allowed to fully ripen on the tree. The color of an olive is not necessarily related to its state of maturity. Many olives start off green and turn black when fully ripe. However, some olives start off green and remain green when fully ripe, while others start of black and remain black. In the United States, where most olives come from California, olives are typically green in color, picked in an unripe state, lye-cured, and then exposed to air as a way of triggering oxidation and conversion to a black outer color. Water curing, brine curing, and lye curing are the most common treatment processes for olives, and each of these treatments can affect the color and composition of the olives.
What’s New and Beneficial About Olives
- Dozens of health-protective nutrients have been identified in olives, and recent studies have taken a very close look at olive varieties, olive processing, and changes that take place in olive nutrients. The overall conclusion from these studies is exciting for anyone who loves olives of all varieties. Greek-style black olives, Spanish-style green olives, Kalamata-style olives, and many different methods of olive preparation provide us with valuable amounts of many different antioxidant and anti-inflammatory nutrients. While there are trade-offs that occur during olive ripening and olive curing—for example, decreased oleuropein with advanced stages of ripening yet increased amounts of anthocyanins—it’s impossible to rule out any single type of olive as being unworthy of consideration as a uniquely health-supportive food, particularly in terms of antioxidant and anti-inflammatory benefits.
- Hydroxytyrosol, an olive phytonutrient that has long been linked to cancer prevention, is now regarded as having the potential to help us prevent bone loss as well. Several recent laboratory animal studies have found increased depositing of calcium in bone and decreased loss of total bone mass following consumption of this olive phytonutrient (as well as oleuropein, another key phytonutrient found in olives). These findings are fascinating, since consumption of a Mediterranean Diet has long been associated with decreased risk of osteoporosis, and olives often find themselves on center stage in Mediterranean Diet studies.
- In traditional herbal medicine practices, preparations from olives and olive leaves have often been used in treatment of inflammatory problems, including allergy-related inflammation. New research may help explain how olives work to provide us with anti-inflammatory benefits, especially during circumstances involving allergy. Olive extracts have now been shown to function as anti-histamines at a cellular level. By blocking special histamine receptors (called H1 receptors), unique components in olive extracts may help to lessen a cell’s histamine response. Because histamine is a molecule that can get overproduced in allergy-related conditions and can be a key player in the inflammatory process, it’s likely that the anti-inflammatory benefits we get from olives involve this anti-histamine pathway. It’s also possible that olives may have a special role to play as part of an overall anti-allergenic diet.
GI: very low
This chart graphically details the %DV that a serving of Olives provides for each of the nutrients of which it is a good, very good, or excellent source according to our Food Rating System. Additional information about the amount of these nutrients provided by Olives can be found in the Food Rating System Chart. A link that takes you to the In-Depth Nutritional Profile for Olives, featuring information over 80 nutrients, can be found under the Food Rating System Chart.
- Health Benefits
- How to Select and Store
- Tips for Preparing and Cooking
- How to Enjoy
- Individual Concerns
- Nutritional Profile
While commonly recognized as a high-fat food (about 80-85% of the calories in olives come from fat), olives are not always appreciated for the type of fat they contain. Olives are unusual in their fat quality, because they provide almost three-quarters of their fat as oleic acid, a monounsaturated fatty acid. (In addition they provide a small amount of the essential fatty acid called linoleic acid, and a very small amount of alpha-linolenic acid, an omega-3 fatty acid.) The high monounsaturated fat content of olives has been associated with reduced risk of cardiovascular disease. When diets low in monounsaturated fat are altered to increase the monounsaturated fat content (without becoming too high in total fat), research study participants typically experience a decrease in their blood cholesterol, LDL cholesterol, and LDL:HDL ratio. All of these changes lower our risk of heart disease.
Recent research studies have also shown that the monounsaturated fat found in olives (and olive oil) can help to decrease blood pressure. The oleic acid found in olives—once absorbed up into the body and transported to our cells—can change signaling patterns at a cell membrane level (specifically, altering G-protein associated cascades). These changes at a cell membrane level result in decreased blood pressure.
In terms of their phytonutrient content, olives are nothing short of astounding. Few high-fat foods offer such a diverse range of antioxidant and anti-inflammatory nutrients—some of which are unique to olives themselves. The list below shows some key phytonutrients in olives, organized by their chemical category:
- Simple Phenols
- Terpenes (including secoiridoids and triterpenes)
- oleanolic acid
- elenoic acid
- Hydroxycinnamic acids
- caffeic acid
- cinnamic acid
- ferulic acid
- coumaric acid
- Hydroxybenzoic acids
- gallic acid
- protocatechuic acid
- vanillic acid
- syringic acid
- Hydroxyphenylacetic acids
- homovanillic acid
- homveratric acid
Given this phytonutrient richness, it’s not surprising that olives have documented health benefits that extend to most of our body systems. Olive benefits have been demonstrated for the cardiovascular system, respiratory system, nervous system, musculoskeletal system, immune system, inflammatory system, and digestive system. We believe that many of these diverse systems benefits are actually related to two underlying health-support aspects of olives, namely, their unusual antioxidant and anti-inflammatory nutrients. In this Health Benefits section, we will focus on those antioxidant and anti-inflammatory properties of olives, as well as some anti-cancer benefits that seem especially important with respect to this food.
The vast majority of olive phytonutrients listed at the beginning of this section function as antioxidants and help us avoid unwanted problems due to oxidative stress. “Oxidative stress” is a situation in which our cells are insufficiently protected from potential oxygen damage, and oxidative stress can often be related to an insufficient supply of antioxidant nutrients. Olives are a good source of the antioxidant vitamin E, and they also contain small amounts of antioxidant minerals like selenium and zinc. However, it’s the phytonutrient content of olives that makes them unique as an antioxidant-rich food.
Perhaps the best-studied antioxidant phytonutrient found in olives is oleuropein. Oleuropein is found exclusively in olives, and it’s been shown to function as an antioxidant nutrient in a variety of ways. Intake of oleuropein has been shown to decrease oxidation of LDL cholesterol; to scavenge nitric oxide (a reactive oxygen-containing molecule); to lower several markers of oxidative stress; and to help protect nerve cells from oxygen-related damage.
One recent study that caught our attention has shown the ability of olives to increase blood levels of glutathione (one of the body’s premier antioxidant nutrients). In a very interesting research twist, study participants were not given fresh olives to eat but rather the pulpy residue from olives that had been previously milled to produce olive oil. Consumption of this olive pulp was associated with significantly increased glutathione levels in the blood of the participants, and improvement in their antioxidant capacity.
Interestingly, there may be common trade-offs made in the levels of different olive antioxidants during the maturation of olives on the tree. For example, the vitamin E content of olives may increase during early ripening when the total phenolic antioxidants in olives are slightly decreasing. Later on in the maturation process, these trends may be reversed.
In addition to their function as antioxidants, many of the phytonutrients found in olives have well-documented anti-inflammatory properties. Extracts from whole olives have been shown to function as anti-histamines at a cellular level. By blocking special histamine receptors (called H1 receptors), unique components in whole olive extracts help to provide us with anti-inflammatory benefits. In addition to their antihistamine properties, whole olive extracts have also been shown to lower risk of unwanted inflammation by lowering levels of leukotriene B4 (LTB4), a very common pro-inflammatory messaging molecule. Oleuropein—one of the unique phytonutrients found in olives—has been shown to decrease the activity of inducible nitric oxide synthase (iNOS). iNOS is an enzyme whose overactivity has been associated with unwanted inflammation. Taken as a group, these research findings point to olives as a uniquely anti-inflammatory food.
The anti-inflammatory benefits of olives have been given special attention in the area of cardiovascular health. In heart patients, olive polyphenols have been determined to lower blood levels of C-reactive protein (CRP). CRP is a widely used blood measurement for assessing the likelihood of unwanted inflammation. Olive polyphenols have also been found to reduce activity in a metabolic pathway called the arachidonic acid pathway, which is central for mobilizing inflammatory processes.
The antioxidant and anti-inflammatory properties of olives make them a natural for protection against cancer because chronic oxidative stress and chronic inflammation can be key factors in the development of cancer. If our cells get overwhelmed by oxidative stress (damage to cell structure and cell function by overly reactive oxygen-containing molecules) and chronic excessive inflammation, our risk of cell cancer is increased. By providing us with rich supplies of antioxidant and anti-inflammatory nutrients, olives can help us avoid this dangerous combination of chronic oxidative stress and chronic inflammation.
Research on whole olives and cancer has often focused on two cancer types: breast cancer and stomach (gastric) cancer. In the case of breast cancer, special attention has been paid to the triterpene phytonutrients in olives, including erythrodiol, uvaol and oleanolic acid. These olive phytonutrients have been shown to help interrupt the life cycle of breast cancer cells. Interruption of cell cycles has also been shown in the case of gastric cancer, but with this second type of cancer, the exact olive phytonutrients involved are less clear.
One of the mechanisms linking olive intake to cancer protection may involve our genes. Antioxidant phytonutrients in olives may have a special ability to protect DNA (deoxyribonucleic acids)—the key chemical component of genetic material in our cells—from oxygen damage. DNA protection from unwanted oxidative stress means better cell function in wide variety of ways and provides cells with decreased risk of cancer development.
From a botanical standpoint, olives belong to a very special group of fruits called drupes. Drupes are fruits that have a pit or stone at their core, and this pit is surrounded by a larger fleshy portion called the pericarp. Other drupes commonly found in diets worldwide include mango, cherry, peach, plum, apricot, nectarine, almond, and pistachio.
There are literally hundreds of varieties of olive trees, but all of them belong in the same scientific category of Olea europea. “Olea” is the Latin word for “oil,” and reflects the high oil content of this food. Olive trees are native to the Mediterranean, as well as different parts of Asia and Africa. Their Mediterranean origins are highlighted in their species name, europea, since countries bordering the north shore of the Mediterranean Sea are typically considered as parts of southern Europe. Olive trees can have remarkable longevity. Most live to an age of several hundred years, and in at least one case, a carbon-dated world record for an olive tree stands at 2,000 years! Although olive trees may produce more olives in lowland terrain, they are comfortable growing in mountainous, rocky conditions and often thrive along the hillsides of Spain, Italy and Greece.
Olives come in many different varieties. In the United States, five varieties account for most commercial production. These varieties are Manzanillo, Sevillano, Mission, Ascolano and Barouni, and all are grown almost exclusively in California. Picholine and Rubra are two additional varieties produced in California in smaller amounts.
Kalamata olives are one olive variety that deserves special mention. Authentic Kalamata olives come from Kalamon olive trees in southern Greece and get their name from Kalamata, their city of origin. European Union (EU) law provides Kalamata olives with Protected Geographical Status and Protected Designation of Origin and does not allow product labeling as “Kalamata” unless the olives have come from this specific area. However, outside of the European Union countries, there are no binding legal standards for labeling of Kalamata olives. In the U.S., many canned and jarred olives are referred to as “Kalamata-style” or “Kalamata-type” olives and these olives are not authentic Kalamata olives grown in the Kalamata area of southern Greece. Genuine Kalamata olives are usually allowed to ripe fully before harvest. Different methods of curing can be used during production of Kalamata olives. Some Greek producers use dry-curing as a method of choice. In dry-curing, olives are covered directly in salt rather than soaked in brine (a concentrated salt liquid). Dry-curing is often used for olives that will be stored for longer periods of time, and Kalamata olives that have been dry-cured can often be identified by their wrinkly skin. Dry-cured Kalamata olives are eventually packaged in olive oil or olive oil/vinegar combinations to which other seasonings are sometimes added. Kalamata olives can also be cured in a salt brine or in water, and in both cases, red wine vinegar and/or red wine are typically used to give the olives their delicious flavors. Most “Kalamata-style” and “Kalamata-type” olives have been cured in this way. Authentic Kalamata olives from southern Greece that have been cured using red wine and/or red wine vinegar are available in many groceries, especially those groceries that stock specialty foods. Genuine Kalamata olives will almost always be labeled as “imported” and may also be labeled as “PDO Kalamata” to reflect their compliance with European Union regulations.
Kalamata are only one among many Mediterranean olive varieties. The list below contains some of the better-known varieties of Mediterranean olives:
- Lecin de Sevilla
- Santa Cateria
- Gordal Sevillana
When freshly picked from the tree, olives often (but not always) have a bitter flavor. This bitterness is related to their phytonutrient content, and especially to their concentration of oleuropein (a secoirodoid terpene). In order to help offset their bitter taste, olives are typically cured. (Curing is also sometimes referred to as “pickling.”) There are three basic types of curing widely used to lower the bitterness in olives. There types are:
Water-curing of olives—just like the name suggests—involves submersion of the olives in water for a period of several weeks or longer. Water-cured olives typically remain slightly bitter because water-curing removes less oleuropein from the olives than other curing methods.
Brine-curing involves the submersion of olives in a concentrated salt solution. Greek style olives in brine and Sicilian style olives in brine are examples of brine-cured olives. Brine-curing can take many months, and olives often undergo fermentation during the brine-curing process. (Fermentation means that the sugars found in olives will often get broken down into lactic or acetic acid, and oleuropein will be freed to migrate into the brine.) Many changes in flavor and phytonutrient composition can take place during the brine-curing process.
Lye-curing involves the submersion of olives in a strong alkali solutions containing either sodium hydroxide (NaOH) or potassium hydroxide (KOH). Lye-curing usually occurs in a series of sequential steps. A first lye bath will cure the skin and outermost portion of the olives. This first solution is then drained from the olives and discarded and the olives are submerged in a second lye solution which begins to cure the next layer of fleshy pulp inside the olive. Up to five lye solutions may be required to cure the entire olive, all the way down to the pit. Dark style ripe olives and green olives are examples of olives that have typically been lye-cured.
During the last stage of lye-curing, oxygen gas is often bubbled up through the lye solution to help darken the olives. In the United States, canned California black olives are typically lye-cured and oxygen-darkened.
Curing is not the only factor that can influence the color of an olive, and it’s worth pointing out that olive color does not automatically indicate anything about the curing process. Many olives start off green and turn black on the tree when fully ripe. Other olives start off green on the tree, remain green when fully ripe, and can only be darkened by curing and/or air exposure. Still other olives start of black on the tree and remain black at full maturity.
Olives have been cultivated in parts of the Mediterranean—including Crete and Syria—for at least 5,000 years. In addition, there is carbon-dating evidence of olive tree presence in Spain as many as 6,000–8,000 years ago. This ancient and legendary tree was also native to parts of Asia and Africa.
It’s not clear exactly how olive trees arrived in the U.S., but it’s clear that the time frame was much later, during the 1500-1700’s. Spanish colonizers of North America definitely brought olive trees across the Atlantic Ocean during the 1500-1700’s, and while some may have been brought directly to the region which is now California, olive trees may also have been brought to the region from Mexico, where cultivation by the Spanish was already underway.
Olives constitute one of the world’s largest fruit crops, with more than 25 million acres of olive trees planted worldwide. (On a worldwide basis, olives are produced in greater amounts than either grapes, apples, or oranges.) Spain is the largest single producer of olives at approximately 6 million tons per year. Italy is second at approximately 3.5 million tons, followed by Greece at 2.5 million. Turkey and Syria are the next major olive producers. Mediterranean production of olives currently involves approximately 800 million trees. 90% of all Mediterranean olives are crushed for the production of olive oil, with the remaining 10% kept in whole food form for eating. In the United States, California’s Central Valley is the site of most olive production, on approximately 27,000 acres.
How to Select and Store
While olives have been traditionally sold in jars and cans, many stores are now offering them in bulk in large barrels or bins (often called an “olive bar”). Buying bulk olives will allow you to experiment with many different types with which you may be unfamiliar and to purchase only as many as you need at one time.
While whole olives are very common, you may also find ones that have been pitted, as well as olives that have been stuffed with either peppers, garlic or almonds. If you purchase olives in bulk, make sure that the store has a good turnover and keeps their olives immersed in brine for freshness and to retain moistness.
When selecting olives from an olive bar, you’ll often be faced with a wide variety of color options and textures. It’s not uncommon to find color varieties of olives that include green, yellow-green, green-gray, rose, red-brown, dark red, purplish-black and black. It’s also not uncommon to find several different textures, including shiny, wilted, or cracked. The size of olives may range from fairly small to fairly large or jumbo. Each of these options among olive varieties can provide you with valuable health benefits. In general, regardless of the variety you choose, select olives that still display a reasonable about of firmness and are not overly soft or mushy.
If you are purchasing olives in a can and don’t use them immediately after opening, they can usually be safely stored in sealed container in your refrigerator for one to two weeks. Whether brine-based, acid-based, or water-based, you can transfer the canning fluid along with the olives into your sealed refrigerator container. Glass jars of olives can be stored directly in the refrigerator for the same period of time, and in the case of some brine-cured olives, for up to one to two months.
When selecting olives, beware of the label description, “hand-picked.” This description does not necessarily tell you anything helpful about the olive harvesting. Many olives are hand-picked, even though the product label makes no mention of this fact. Conversely, olives with have been mechanically harvested with a hand-held pneumatic rake are sometimes labeled as “hand-picked.”