Ultimate Guide to Olive Oil

The craft of turning olives into oil has been honed in the Mediterranean region over thousands of years, and techniques have been passed down from generation to generation. The process is truly a regional art. The method used in Greece is different from the one used in Spain, and each individual grower might have a unique way of tending the trees and producing the tasty liquid gold.

Mediterranean olive trees must mature for several years before they produce olives. Careful pruning optimizes the number of olives a single tree will bear. A meticulous hand is necessary because it takes at least ten pounds of olives to produce one liter (about four cups) of olive oil.

Hundreds of olive varieties exist, but only several dozen are grown commercially around the world. Some varieties are bursting with health-promoting polyphenols, while others contain few. The type of olive used to make any particular bottle of oil is rarely listed on the label. However, for those labels that do have the information, the following table, which shows which olives are richest in beneficial polyphenols, will be helpful.

The time at which olives are harvested also plays a major role in flavor and polyphenol content. The peak time is a short period right as the olives ripen. Olives are at their prime for only about two or three weeks. Healthy compounds then rapidly diminish over the next two to five weeks.

Picking Particulars

It takes quite a bit of work to coax oil out of olives. Traditionally, trees were shaken or beaten with sticks to make the olives drop to the ground. Such tough treatment is not good for olives, however. Tumbling out of a tree and plopping onto the ground causes bruising.

Soft fruits, such as peaches and plums, wouldn't take kindly to this type of treatment; they would bruise, too, and we would never think of harvesting them this way. Olives are also soft fruits that should be treated delicately because once they bruise, the beneficial oils within start to degrade.

Some olive oil labels declare that their bottles' contents are made from handpicked olives. This typically denotes a better-quality oil. Some growers separate their olives into "ground" olives (those collected from the ground) and "tree" olives (those picked from the tree) and use them for different grades of oil. Many large-scale growers use a tree-shaking device and set up nets beneath the trees that catch the olives before they hit the ground.

Growers must be careful when transporting olives from the trees to the processing plant. Olives are best carried in shallow containers so they don't pile up too deeply and crush one another. Any damage to the olives can trigger oxidation and fermentation, which create an "off" flavor. Olives should be processed soon after harvest because storing them also diminishes their quality.

Press Time

After olives are picked, any leaves, twigs, and stems are removed, and the olives are washed. Then it's time for pressing. Back in the old days, processors used stone or granite wheels to crush the olives.

Today, stainless steel rollers crush the olives and pits and grind them into paste. The paste then undergoes malaxation, a process in which water is slowly stirred into the paste. Malaxation allows the tiny oil molecules to clump together and concentrate.

The mixture is stirred for 20 to 40 minutes. Longer mixing times increase oil production and give the oil a chance to pick up additional flavors from the olive paste. However, the mixing also exposes the oil to air, producing free radicals that poorly affect its quality.

Modern systems use closed mixing chambers filled with a harmless gas to prevent oxidation. This method increases yield and flavor and preserves quality. The mixture may be heated to about 82 degrees Fahrenheit, which further increases yield but does allow some oxidation. This temperature is low enough to be considered "cold pressed."

Next, the paste is put on mats and further pressed or sent through a centrifuge (a compartment that is rotated on a central axis at extreme speed to separate materials). When the centrifuge spins, the olive paste remnants are pushed to the sides of the compartment cylinder while water and oil are extracted from the center of the centrifuge. The oil and water are later separated.

The solid material that remains after the extraction of the oil is called pomace, and it contains residual oil. Some manufacturers will use steam, hexane, or other solvents to squeeze more oil out of the pomace. This low-quality oil must be labeled as pomace oil.

Oil may then be refined, bleached, and/or deodorized. Refining reduces acidity and any bitter taste. Bleaching removes chlorophyll and carotenoids (naturally occurring pigments that give plants their colors) and possibly pesticides, resulting in a light-colored oil with fewer nutrients. Deodorizing removes the fragrant aroma of the olive oil.

In the manufacturing plant, oil is stored in stainless steel containers at about 65 degrees Fahrenheit to prevent breakdown before it is bottled and shipped.

Lots of different types of olive oil come out of the presses. On the next page you'll learn what all the label terms mean and what's inside each of the bottles.

 

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Rich, beautiful, and fragrant, olive oil is much like wine -- taste is a matter of personal preference. The many variables that go into the production of olive oil yield dramatic differences in color, aroma, and flavor. And several names are used to differentiate all of these versions, which you'll learn about here.

The following factors impact the taste of olive oil:

Olive oils are graded by production method, acidity content, and flavor. The International Olive Oil Council (IOOC) sets quality standards that most olive-oil-producing countries use, but the United States does not legally recognize these benchmarks. Instead, the U.S. Department of Agriculture uses a different system that was set up before the IOOC existed. However, American olive growers and oil importers are encouraging the USDA to adopt standards similar to those of the IOOC.

Where in the World?

When buying olive oil, you'll see varieties from all over the globe. Most of the world's supply is produced from olives grown in Spain, Italy, and Greece, but other areas, including France and California, are in on the fun, too. Here's what you need to know about olive oil and geography:

Olives from different countries are often blended together to produce an oil variety. Or, olives from diverse areas of one country may be combined. These bulk-blended oils are the most economical but are still high quality. On the other hand, some producers only use olives that are grown in a specific area of a country. These regional oils are usually known for their unique flavors.

Estate olive oils are the cream of the crop. Estate oils are produced using olives from a single olive farm. These olives are usually handpicked, then pressed and bottled right at the estate. Expect to get the best flavor out of these varieties, but also expect to pay more.

Making the Grades

There are three basic grades of edible olive oil, and several types within each grade. Extra virgin includes "premium extra virgin" and "extra virgin"; virgin comprises "fine virgin," "virgin," and "semifine virgin"; and olive oil includes what used to be called "pure olive oil" and "refined oil."

All types of extra-virgin and virgin oils are made from the first pressing of the olives, which removes about 90 percent of the olives' juice. Chemicals and high heat are not allowed in the production of extra-virgin or virgin oils -- no further processing or refining occurs after the pressing process. Neither extra-virgin nor virgin oils are allowed to contain any refined olive oil.

Virgin olive oils

At the head of the olive oil class sit the extra-virgins, followed closely by the virgins. The difference between two oils and where they rank in the following hierarchy may be just half a percentage point of acidity. However, that is all it takes to distinguish between a very good oil and a great oil.

"Premium extra-virgin olive oil" is nature's finest, thanks to its extremely low acidity (possibly as low as 0.225 percent). It is best suited for using uncooked in dishes where you can appreciate its exquisite aroma and flavor. Try it in salads, as a dip for bread, or as a condiment.

"Extra-virgin olive oil" has a fruity taste and may be pale yellow to bright green in color. In general, the deeper the color, the more flavor it yields. IOOC regulations say extra-virgin olive oil must have a superior flavor and contain no more than 0.8 percent acidity, but other regulators set the acidity cut-off point at 1 percent. As with the premium version, it is best to use extra-virgin olive oil uncooked in order to appreciate its flavor.

"Fine virgin olive oil" must have a "good" taste (as judged by IOOC standards) and an acidity level of no more than 1.5 percent. Fine virgin olive oil is less expensive than extra-virgin oil but is close in quality and is good uncooked.

"Virgin olive oil" must have a "good" taste, and its acidity must be 2 percent or less. Like other virgin oils, it cannot contain any refined oil. Virgin olive oil is good for cooking, but it also has enough flavor to be enjoyed uncooked.

"Semifine virgin olive oil" must have an acidity no higher than 3.3 percent. It is good for cooking but doesn't have enough flavor to be enjoyed uncooked.

Lower-quality oils

Some olive oil is further refined after the first pressing. These three types of oils can no longer bear the title "virgin."

When virgin oils are not fit for human consumption (because of poor flavor, an acidity level greater than 3.3 percent, or an unpleasant aroma), they are sent to a processing plant where they become "refined olive oils." There they undergo processing with agents that might include heat, chemicals, and/or filtration.

These refined olive oils become clear, odorless, and flavorless and have an acidity level of 0.3 percent or less, which gives them a long shelf life (refined olive oils' only real advantage). They are typically blended with virgin oils, used in cooking, or used for foods that are labeled "packed in olive oil."

The current "olive oil" category used to be called "pure olive oil." Today, oils in this classification are a blend of refined olive oil and a virgin olive oil. The virgin oil lends a little aroma and flavor to the final product, which can have an acidity level of no more than 1.5 percent. In most cases, oils in this category contain about 85 percent refined oil and 15 percent virgin or extra-virgin oil. Oils of the "olive oil" grade withstand heat well.

"Olive pomace oil" is made from the olive paste that is left in the centrifuge after the olives are pressed and the oil-water mixture is extracted. Olive pomace oil can be treated with heat and chemicals to extract additional oil (about 10 percent of the original amount of oil in the olives). Its acidity cannot exceed 1.5 percent.

Virgin oil may be added to pomace oil for color and flavor. Olive pomace oil is edible, but it may not carry the name "olive oil." This oil is most often used commercially and is rarely seen on the grocer's shelf.

Other oils

Sometimes, cooks don't need the full flavor of olive oil, or they need a little extra taste added. Oil producers have responded to these needs by creating lite olive oil and flavored oils.

"Lite olive oil" is also called "light" or "mild" oil. These oils have undergone an extremely fine filtration process (without the use of heat or chemicals) to remove most of the natural color, aroma, and flavor. This makes them suitable for cooking or baking in recipes in which a fruity olive flavor isn't needed. The terms "lite," "light," and "mild" can be used along with "extra virgin olive oil," "virgin olive oil," and "olive oil."

In this case, "lite" or "light" do not refer to fat content. These oils contain the same amount of fat and calories as any other olive oil (about 13 grams of fat and 120 calories per tablespoon). The classifications instead refer to the oil's lighter color and flavor.

Do you want oil with more flavor rather than less? Some manufacturers make high-quality flavored olive oils by adding sweet or savory ingredients, such as spices, herbs, vegetables, or citrus peel, to extra-virgin oils during the pressing process. Lower-quality flavored oils have these ingredients added after pressing.

Commercially prepared flavored oils are usually safe to keep and use for a long period of time, but homemade ones are not. If you create your own homemade flavored oils, make only small amounts that you can use within several days, and always store them in the refrigerator to prevent the growth of potentially harmful bacteria. The oil itself does not support bacterial growth, but the moisture and nutrients in fresh herbs, garlic, dried tomatoes, or citrus peels do.

Color Considerations

Green olive oils come from unripe olives and impart a slightly bitter, pungent flavor. Emerald-tinged oils have fruity, grassy, and peppery flavors that dominate the foods in which you use them. These oils are great with neutral-flavored foods that allow their bold flavors to shine. You can pair green olive oils with strongly flavored foods as long as they complement the oils' pungent tastes.

Olive oils that glimmer with a golden color are made from ripe olives. Olives turn from green to bluish-purple to black as they ripen. Oils made from ripe olives have a milder, smoother, somewhat buttery taste without bitterness. These oils are perfect for foods with subtle flavors because the gentle taste of a ripe olive oil won't overshadow mildly flavored foods.

Organic Olive Oil

All plants have natural enemies, and olive trees are no different. Olives are susceptible to a pest known as the olive fly, which lives inside the olive and makes a feast of the fruit. Fungus is another adversary of olives, although olive flies are a bigger threat.

Growers use pesticides, fungicides, and herbicides to protect their crops when necessary. If you'd like to avoid these chemicals, buy organic olive oil.

In the United States there are strict guidelines governing the use of the term "organic" on labels. If the label says "USDA Certified Organic," the producer has proven to the U.S. Department of Agriculture that the oil is made with olives that were grown without chemicals, among other requirements. The regulations apply whether the olives are grown and bottled in the United States or imported from other countries.

When you pick the type you like, it can last for months properly stored. On the next page you'll learn how to prevent a breakdown of the nutrients in olive oil.

 

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Because of olive oil's high monounsaturated fat content, it can be stored longer than most other oils -- as long as it's stored properly. Oils are fragile and need to be treated gently to preserve their healthful properties and to keep them from becoming a health hazard full of free radicals.

When choosing your storage location, remember that heat, air, and light are the enemies of oil. These elements help create free radicals, which eventually lead to excessive oxidation and rancidity in the oil that will leave a bad taste in your mouth. Even worse, oxidation and free radicals contribute to heart disease and cancer.

Rancidity can set in long before you can taste it or smell it. Rotten oils harm cells and use up precious antioxidants. Even though rancid oil doesn't pose a food-safety type of health risk, the less you consume, the better.

The best storage containers for olive oil are made of either tinted glass (to keep out light) or a nonreactive metal, such as stainless steel. Avoid metal containers made of iron or copper because the chemical reactions between the olive oil and those metals create toxic compounds. Avoid most plastic, too; oil can absorb noxious substances such as polyvinyl chlorides (PVCs) out of the plastic. Containers also need a tight cap or lid to keep out unwanted air.

Keep It Cool

Temperature is also important in preventing degradation of olive oil. Experts recommend storing the oil at 57 degrees Fahrenheit, the temperature of a wine cellar. Aren't lucky enough to have a wine cellar? A room temperature of about 70 degrees Fahrenheit will be fine. If your kitchen is routinely warmer than that, you can refrigerate the oil.

In fact, refrigeration is best for long-term storage of all olive oils except premium extra-virgin ones. Consider keeping small amounts of olive oil in a sealed container at room temperature -- perhaps in a small, capped porcelain jug that keeps out air and light. This way, your olive oil is instantly ready to use. Keep the rest in the refrigerator, but remember that refrigerated olive oil will solidify and turn cloudy, making it difficult to use. Returning it to room temperature restores its fluidity and color.

Another option is to store olive oil in a wide-mouth glass jar in the refrigerator. Even though it solidifies, you can easily spoon out any amount you need. A clear jar is fine because it's dark inside the refrigerator most of the time.

If you don't want to refrigerate your olive oil, keep it in a dark, cool cupboard away from the stove or other heat-producing appliances. Olive oil connoisseurs recommend storing premium extra-virgin olive oils at room temperature. If refrigerated, condensation could develop and adversely affect their flavor. Refrigeration does not affect the quality or flavor of other olive oils.

Olive oil will keep well if stored in a sealed container in a cool, dark cupboard for about one year. If unopened, the oil may keep for as long as two years.

Older Isn't Better

Unlike wine, oil does not improve with age. As olive oil gets older, it gradually breaks down, more free oleic acid is formed, the acidity level rises, and flavor weakens. Extra-virgin oils keep better because they have a low acidity level to start with, but you should use lower-quality oils within months because they start out with higher acidity levels. As oil sits on your shelf, its acidity level rises daily, and soon it is not palatable.

You'll get the best quality and flavor from your olive oil if you use it within a year of pressing. Olive oil remains at its peak for about two or three months after pressing, but unfortunately, few labels carry bottling dates or "use by" dates, let alone pressing dates.

More is at issue than flavor, however. Research shows the nutrients in olive oil degrade over time.

In a study that appeared in the May 2004 issue of the Journal of Agriculture and Food Chemistry, Spanish researchers tested virgin olive oil that had been stored for 12 months under perfect conditions.

What they found was quite surprising: After 12 months, many of the oil's prime healing substances had practically vanished. All the vitamin E was gone, as much as 30 percent of the chlorophyll had deteriorated, and 40 percent of the beta-carotene had disintegrated. Phenol levels had dropped dramatically, too.

Instead of stashing your olive oil in the cabinet, why not unleash its flavor on your favorite foods? The next page has tons of tips for how to use olive oil.

 

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Olive oil helps carry the flavor of foods and spices, provides a pleasing feel in the mouth, and satisfies the appetite. Liberal use of it will enhance both savory and sweet dishes without guilt because of its wonderful health-boosting properties (although if you're trying to lose weight, you may not want to overdo it, because like all fats, it provides nine calories per gram).

Virgin and extra-virgin oils are best used uncooked or cooked at low to medium temperatures. Refined and olive oil grade oils are the choices for high-heat uses, such as frying.

An oil's smoke point is the temperature at which it smokes when heated. Any oil is ruined at its smoke point and is no longer good for you. If you heat an oil to its smoke point, carefully discard it and start over. Olive oil has a higher smoke point than most other oils (about 400 degrees Fahrenheit). Refined olive oils have a slightly higher smoke point (about 410 degrees Fahrenheit).

Tips for Cooking with Olive Oil

Although extra-virgin and virgin olive oils stand up to heat remarkably well, they do lose flavor as they're heated, so they are best for uncooked dishes. Use them to harmonize the spices in a dish, to enhance and build flavors, and to add body and depth.

Olive oil also balances the acidity in high-acid foods, such as tomatoes, vinegar, wine, and lemon juice. In general, treat your olive oils as you do your wines, carefully pairing their tastes with the flavors of the other ingredients in the dishes you are creating.

Here are some ways to use olive oil:

The Most Versatile Version

You can use multipurpose fine virgin olive oil in almost any recipe. It is moderately priced despite being close in flavor to more expensive extra-virgin olive oils. Plus, you can use it in high-heat applications, so feel free to grab fine virgin olive oil when you need to saute, panfry, or stir-fry.

Fine virgin olive oil is also the right choice when you want quality flavor but not that strong olive taste. Try these tips for fine virgin olive oil in your kitchen:

Baking with Olive Oil

Most people don't think of using olive oil when baking, but it's actually a great way to get more monounsaturated fat and polyphenolic compounds in your diet. Choose the lite, light, or mild type of olive oil for baking, especially savory breads and sweets such as cakes, cookies, and other desserts. Because of the filtration these types of oils have undergone, they withstand high-heat cooking methods.

Substituting olive oil for butter dramatically reduces the amount of fat -- especially saturated fat -- in your baked goods. And of course, olive oil does not contain any of butter's cholesterol. You'll also use less fat -- you can substitute three tablespoons of olive oil for a quarter-cup of butter. (Check your cookbook for substituting advice.)

The product still turns out as expected, but with 25 percent less fat, fewer calories, and more heart-healthy nutrients.

Olive oil can enhance the flavor of almost anything you eat. Now that you know how it gets to your table, you'll know how to get the most out of it.

 

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ABOUT THE AUTHOR

Gayle Povis Alleman is a registered dietitian with a bachelor's degree in traditional nutrition from Western Washington University and a master's degree in alternative nutrition from Bastyr University. This varied background allows her to bring together the best of both approaches to offer research-based, holistic information about wholesome foods, nutrition, and health. As a writer, educator, and speaker, she encourages people to achieve optimum health through food, nutrients, and physical activity.