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Best Practices

Oct 21, 2013
This section provides Best Practices for olive growers and olive oil processors, buyers and consumers. These Best Practices were developed with funding support from the United States Department of Agriculture and the California Department of Food and Agriculture.
  • Best Practices for Growers

    These Best Practices are based on California research conducted by UC Davis, UC Cooperative Extension (UCCE) and UC Agricultural and Natural Resources (ANR). They were prepared by the UC Davis Olive Center and G. Steven Sibbett, UCCE Farm Advisor Emeritus, Dr. Louise Ferguson, ANR Extension Specialist and Dr. Elizabeth Fichtner, UCCE Farm Advisor. We recommend that growers also review comprehensive research information available through ANR, including the Olive Production Manual, Organic Olive Production Manual and UC IPM Online.

    • Siting an Olive Orchard

      climate.jpg
      Know the climate
      Know the site’s climate. It is critical to assess climate before planting olives in a particular site:

      • Winter. Ideally, winter temperatures should fluctuate between 35 °F (2 °C) and 65 °F (18 °C). Temperatures below freezing cause progressively more tree damage, from small shoot and branch lesions that provide entry points for olive knot bacteria at 23 °F to 32 °F (-5 °C to 0 °C), greater tissue damage at 14 °F to 23 °F (-5 °C to -10 °C) and death of large limbs and entire trees at temperatures below 14 °F (-10 °C).
      • Spring. The bloom development period should be free of prolonged cold and wet or hot and dry weather. These conditions hinder flower development, pollination, fertilization and fruit set. Long or sudden cold spells particularly increase the negative impact.
      • Summer. Long, warm and dry summers promote good fruit development. Avoid areas with summer rainfall and high humidity, which promote fungal and bacterial diseases.
      • Fall. Temperatures below freezing often damage processing quality of fruit destined for either table or oil. Pay special attention to low-lying areas, which are especially vulnerable to colder temperatures. Fall rains improve size and value of fruits destined for table processing, but make fruit destined for oil processing more susceptible to damage, fermentation and mold and may contribute to emulsions that hinder oil extraction Rains at harvest can also hinder mechanical harvest equipment from accessing the orchard.

      sitehistoryverticilliumwilt.jpg
      Research the history
      Research the site history. Find out crop history from the previous landowner and, where relevant, the local agricultural commissioner’s office. Avoid soil previously planted with crops (such as cotton, cucurbits, eggplant, peppers, potato, or tomato) susceptible to the Verticillium wilt fungus, a soil-borne disease that kills olive trees. There are limited Verticillium wilt management strategies available to growers.

      soilprofile.jpg
      Analyze the soil profile
      Analyze the soil profile. Managed correctly, olives perform well in many soils, even those considered marginal in quality. Soil maps do not provide sufficient detail for specific orchard sites. Use a backhoe or augur and dig pits in representative places on the planting site. Examine the soil’s physical condition, including layers that are texturally different, to identify limitations on root and water penetration. Olives do not grow well in poorly drained soils. The best and most productive soils are those un-stratified, moderately fine-textured of at least 4 ft (1.2 m) in depth.

      soilsample.jpg
      Determine soil chemistry
      Determine the soil chemistry. Take a representative soil sample from the orchard site and submit it to a laboratory for analysis. The best soils are those moderately acid to moderately alkaline (pH between 6.5 to 8.5). Soil below pH 5.5 can have aluminum and manganese toxicity, while soil above pH 8.5 have poor structure and may have sodium toxicity. Avoid soils high in salinity (≥4 dS/m). To avoid water penetration problems due to poor soil structure, avoid soils with an exchangeable sodium percentage of > 4 or be prepared to amend such soils to leach excessive sodium.Avoid soils with excessive boron (≥2 ppm), and chloride (10-15 meq/l) as these conditions may reduce productivity unless corrected or managed with soil amendments requiring additional expense.

      Asses water availability
      Asses water availability
      Assess water availability. Although olive trees are drought tolerant, they will grow faster and produce more consistently in California with supplemental irrigation. Supplemental irrigation water can be available as irrigation district water (surface water) or by farm wells. Sites served only by irrigation districts are at risk of water shortage during drought years.Inadequate water during floral development can lead to poor fruit set especially if adverse weather occurs during or shortly after bloom. Inadequate water through the growing season can limit fruit size for table olive growers. Choose sites that can supply olive trees with approximately three acre-feet per year for table olives and two acre-feet per year for oil olives, although more water will be necessary if irrigation efficiency is compromised by conditions such as runoff or poor weed control.

      Evaluate water quality. Knowing the site’s water chemistry will help growers manage chemical hazards and avoid excessive fertilizer use that increases orchard maintenance cost, reduces productivity and potentially pollutes water sources. Excessive sodium in water supplies concentrate in soil, causing infiltration problems. High nitrogen levels produce excessive vegetative growth hindering fruit production, encourages pest development (e.g. black scale) and adds additional pruning expense. Take a water sample and request a qualified laboratory to conduct an analysis of the elements in this table.

      WATER ANALYSISLIMIT
      Acidity/alkalinity (pH) 6.5 – 8.5
      Electrical conductivity (ECw) < 3.0 dS/m
      Exchangeable sodium percentage (ESP) < 4
      Bicarbonate (HCO3-) < 3.5 meq/l
      Sodium absorption ratio (SAR) <6
      Chloride (Cl-) <3 meq/l
      Boron (B+) ≤ 1 - 2 mg/l
      Nitrate nitrogen (NO3-N) <5 ppm

      Assess infrastructure. Ensure essential supplies and services are within a reasonable distance from the orchard. An isolated orchard requires excessively high costs to extend transportation and water infrastructure, obtain essential supplies and services, access labor and deliver the crop.

    • Establishing a Hedgerow Olive Orchard

      • Introduction

        Traditional California olive orchards were large trees at planted at low densities; typically less than 85 trees/ac (205 trees/ha), hand-harvested and hand-pruned. Increasing harvest costs and uncertain labor availability have resulted in many California olive oil growers and a few table olive growers planting higher-density, hedgerow configured orchards. In hedgerow orchards, both the in-row and between-row spacing is tighter, ranging from “high-density” (HD) orchards of about 200 trees/ac (482 trees/ha) to “super-high-density” (SHD) orchards of about 650 trees/ac (1567/ha). Both HD and SHD orchards facilitate mechanical harvesting and pruning while also intercepting the optimal percentage of incident light to maximize yield.

        Most California olive oil acreage favors the SHD format, which requires clones of specific varieties developed for these orchards. Typically SHD oil olives are harvested with over-the-row, canopy-contact harvesters. A few California olive oil growers and table olive growers have adopted HD orchard densities, which can be harvested with trunk shakers for the first 15 years, and then possibly harvested with canopy-contact equipment when trunk-shaking efficiency declines. University of California (UC) researchers have developed specifications for an efficient canopy-contact harvester head for oil and table olive hedgerow orchards. UC has provided these specifications to commercial harvest equipment manufacturers.

        UC cost studies for establishing and producing table and oil olives in a hedgerow orchard are available at http://coststudies.ucdavis.edu/. UC cost studies are based on specific assumptions -- but not all practices, and particularly quoted prices, may be applicable to every grower’s situation. Growers should use these cost studies as beginning templates and modify them to a given situation and local costs. The grower then can use the ranging analyses in the studies to determine if table or oil olive production is feasible in a specific location.

        The following best practices for establishing hedgerow orchards were based on UC research. When UC data-based information was unavailable, the best practices were based on research outside of California as well as current predominant California industry practices. Except where indicated, the recommendations apply whether the orchard is intended for oil, table or dual varieties.

      • Variety Selection

        Nurseries may need a year’s notice to ensure selected varieties are available for spring planting. California’s “ripe” table olive processors primarily favor Manzanillo with Sevillano (Gordal) as a pollinizer, while Sicilian-style and Spanish-style processers prefer Sevillano (Gordal). Small table olive processors have used other varieties for these and other curing styles. Arbequina is California’s most widely planted oil variety, although California oil producers have marketed all varieties in the table below as single-varietal olive oils, even traditional table olive varieties such as Ascolano, Mission, Sevillano and Manzanillo.

        When selecting varieties, consider:

        • processor preferences
        • cold hardiness
        • disease resistance
        • vigor and yield
        • pollination requirements (most olive varieties perform better with an appropriate pollinator variety planted no more than 200 ft (61 m) away

        When choosing varieties for olive oil processing, also consider:

        • oil content
        • extraction efficiency
        • flavor characteristics
        • stability (which correlates with high polyphenol levels and high oleic acid content)

        When choosing varieties for table olive processing, in general, also consider:

        • high flesh-to-pit ratio
        • large fruit size (larger sizes typically receive a higher price than smaller sizes)
        • excellent flesh quality (such as resistance to bruising if the olives will be cured green, and desirable sensory characteristics for the anticipated curing method)

        No single olive variety has every desirable characteristic. Comparison of some common olive varieties are in the table below, primarily based on information from the World Catalogue of Olive Varieties, modified by other sources to include varieties not addressed in the catalogue.

        VARIETY

        USE

        OIL

        OLIVE FLY

        VERTICILLIUM WILT

        PEACOCK SPOT

        OLIVE

        KNOT

        COLD

        RIPENING

        VIGOR

        PRODUCTIVITY

        ARBEQUINA*

        Oil

        High

        Sensitive

        Sensitive

        Sensitive

        Medium

        Resistant

        Early-Mid

        Low

        High & constant

        ARBOSANA*

        Oil

        High

         

         

        Sensitive

        Sensitive

        Sensitive

        Early-Mid

        Low

        High & constant

        ASCOLANO

        Table

        Medium

        Sensitive

         

        Resistant

        Resistant

        Resistant

        Early

        High

        Med & constant

        CORATINA

        Oil

        High

         

         

         

         

        Resistant

        Late

        Medium

        High & constant

        FRANTOIO

        Oil

        Medium

        Sensitive

        Resistant

        Sensitive

        Sensitive

        Sensitive

        Late

        Medium

        High & constant

        HOJIBLANCA

        Dual

        Medium

        Medium

        Sensitive

        Sensitive

        Sensitive

        Resistant

        Late

        Med-High

        High & alternate

        KALAMON

        Dual

        Medium

        Resistant

        Sensitive

        Sensitive

        Resistant

        Medium

        Late

        High

        High & alternate

        KORONEIKI*

        Oil

        High

         

        Medium

        Resistant

        Sensitive

        Sensitive

        Early-Mid

        Medium

        High & constant

        MANZANILLO

        Table

        Medium

        Sensitive

        V.Sensitive

        Sensitive

        Sensitive

        Sensitive

        Early

        Low-Med

        High & alternate

        MISSION

        Dual

        High

         

        Sensitive

        Sensitive

        Resistant

        Resistant

        Late

        High

        Med & alternate

        PICHOLINE

        Dual

        Medium

        Medium

        Medium

        Resistant

         

        Medium

        Late

        Medium

        High & constant

        PICUAL

        Oil

        High

        Sensitive

        Sensitive

        Sensitive

        Resistant

        Resistant

        Early

        Medium

        High & constant

        SEVILLANO

        Table

        Low

        Sensitive

         

        Resistant

        Sensitive

        Resistant

        Early

        Med-High

        Low & alternate

        TAGGIASCA

        Oil

        High

        Sensitive

         

         

        Sensitive

        Sensitive

        Late

        High

        High & constant

        * IRTA considers the Arbequina SHD clone to be sensitive to peacock spot while the World Catalogue of Olive Varieties lists Arbequina as resistant to the disease. Arbosana SHD clone information is from California nurseries and California field observations. California field observations indicated Koroneiki SHD clones as high & alternate bearing rather than high & constant bearing as indicated by the World Catalogue of Olive Varieties.

      • Prepare soil

        Soils that do not have a minimum, un-stratified depth of 4 ft (1.2 m) will need to be deep-tilled to 3 - 5 ft (1 - 1.5 m) to ensure uniform water penetration. Use a slip plow to mix stratified soils and a ripper to break up cemented hard pans. The best time for deep tillage is when soils are dry.

        Till un-stratified sub-soils to 2.5 ft (0.7 m) by chiseling and shallow ripping to break up compacted plow pans, thereby improving drainage and facilitating root development. Till when soils are dry to avoid compacting soil.

        Super-high-density orchards in California have accommodated harvest equipment with grades as high as 15 percent, but grades above 6 percent can lead to severe erosion if not designed properly.

        Control weeds prior to planting as weeds will compete with trees for water, nutrients and sunlight, thereby delaying production. Control annual weeds by disking or applying pre- or post-emergent herbicides. Control most perennial weeds (e.g., bermudagrass, dallisgrass, and johnsongrass) by repeated disking and drying during summer. Control field bindweed by irrigating to produce a vigorous plant and then treating with glyphosate or 2,4-D, followed in 10 days by disking and drying the soil.

        Add soil amendments (such as gypsum, sulfur, sulfuric acid and lime) if necessary to correct sodic (alkali), acid (pH7) in reaction. A thorough soil analysis through the profile is essential to determining need for, type, and amount of chemical amendments prior to planting.

        Consider establishing berms, which are flat, raised strips of soil of about 1.5 ft (50 cm) high and 3.5 ft (1 m) wide located within the tree row on which orchard trees are planted. Berms can allow better moisture retention and facilitate drainage, but they can also limit irrigation hose placement and decrease trellis integrity. Berms may also decrease drainage thereby increasing the potential for root disease when the orchard slope is perpendicular to the berms. Berms are have been more useful in rainy Northern California orchards to promote drainage away from the tree but generally are not employed in drier Southern California orchards.

      • Determine orchard design

        High-Density (HD) hedgerow orchards in California have ranged from 200 trees/acre to 269 trees per acre, while Super-High-Density (SHD) hedgerow orchards, which are used exclusively for oil production, have ranged from 453 trees/acre to 908 trees/acre, with most SHD orchards planted at about 650 trees/ac (1567/ha).

        Tree spacing in hedgerow orchards should be dictated by harvest equipment. Most SHD olive oil growers use over-the-row harvesters while UC research has demonstrated trunk shakers and canopy-contact harvesters can be efficient for HD table olive harvesting. The SHD system works best with clones of specific varieties such as Arbequina, Arbosana and Koroneiki, while the HD system can accept many olive varieties.

        In general, SHD orchards are more expensive to establish than HD orchards, but SHD orchards will achieve maximum income sooner than HD orchards. Both orchards have similar maximum income and expenses over time based on data from the Australian olive oil industry.

        North-south oriented hedgerows will maximize sunlight exposure, decrease humidity and reduce wind resistance.

        Plant pollinizer trees or rows no more than every 200 feet (61 m) to ensure that wind-blown pollen is most effectively distributed.

      • Install trellis and stakes

        A trellis and tree stakes support trees, prevents misshapen trees due to wind and ensures a straight tree row to facilitate the over-the-row harvesters in SHD olive oil orchards. A trellis is essential in an SHD orchard but not essential or usually needed in HD orchards. Stakes, however, are necessary to develop a straight single trunk.

        Trellis and stakes. A standard SHD trellis uses 8 ft (2.4 m) treated round end posts, with 8 ft (2.4 m) metal T-posts placed at 55 ft (16.8 m) intervals and 12-gauge galvanized wire installed at 4.5 ft (1.4 m) and 6 ft (1.8 m), secured to the T-posts and bamboo tree stakes with wire clips. SHD growers in California are moving toward smaller trellises with 6 ft (2 m) end posts and 6 ft (2 m) T-posts driven 2 ft (0.6 m) into the ground, and a single wire placed at 3 ft (1 m). If one wants to use a trellis in a standard HD orchard, use 12 ft (3.7 m) treated-wood or iron posts that are round or 4 x 4 inches (10 x 10 cm) square, placed at the ends of rows and at 100 ft (30 m) intervals, with 12-gauge galvanized wire installed at 3, 6 and 9 ft (1, 2, and 3 m.) SHD and HD trellised orchards provide a 7 ft (2.1 m) bamboo stake at each tree and tie the central leader to the stake at 8 to 14 inch (20 to 35 cm) intervals as the leader grows.

        Stakes only. When using stakes without a trellis in an HD orchard located in windy areas, use treated wood stakes that are 2 x 2 inches (5 cm) square and 8 ft (1.5 to 2.5 m) in height. Tie the central leader to the stake at 2.5 ft (75 cm) intervals. Lighter bamboo stakes can be used in areas with little wind.

      • Select the irrigation system

        A micro-irrigation system such as drip, fan jet, or micro-sprinkler, provides higher efficiency (85-95%) than large sprinklers (75-85%) or furrow irrigation (65-75%) by minimizing water losses due to runoff and evaporation. The higher efficiency of micro-irrigation systems also reduces orchard humidity compared to larger sprinklers, reducing risks related to fungal diseases.

        Micro-irrigation systems are often designed to permit fertigation, the application of plant nutrients or water amendments in the irrigation water. Fertigation has the advantages of maintaining moisture in the wetted area, encouraging the development of new roots, extending the period of maximum root activity, improving plant nutrient absorption and providing a constant supply of nutrients based on the tree’s needs. The two objectives of fertigation are to maximize profit and reduce adverse environmental effects. Profit is maximized when fertilizer remains in the wetted zone where root density is greatest. Adverse environmental impacts are minimized by not allowing fertilizer to leach below the wetted root zone and pollute groundwater.

        Filtration is a significant cost in installing micro-irrigation systems and is essential to mitigate clogging due to bacterial growth. Chemigation valves are also required to prevent back flow of chemicals as well as chemical precipitation in the laterals and emitters.

        Maximizing benefits from drip and micro-irrigation systems requires the system to be designed properly, installed correctly and managed effectively. Neglecting these factors can lead to poor results.

        Install the irrigation system prior to planting. Irrigate the orchard prior to planting if soils are dry. Planting in dry soil will cause moisture to migrate from the root ball to the soil, resulting in root death in very young trees.

      • Train the new trees

        There are two objectives to tree training during the first three years: (1) developing a sturdy, well-spaced framework of uncongested scaffold branches to support heavy crops and mechanical harvesting, and (2) bringing the tree into bearing as quickly as possible. Pruning must be sufficient to achieve the first objective, but minimized to promote the second.

        Avoid training and pruning during dormancy. Such pruning requires heavier cutting and renders the tree more susceptible to freeze injury and disease.

        For HD orchards, remove shoots below a 2.5 ft (75 cm) height, and pinch the leader at 36 to 40 inches (1 m) to stimulate lateral growth if lateral shoots above 2.5 ft (75 cm) have not already begun in the nursery. Remove suckers and waterspouts (which are the angular, succulent herbaceous growth, often pale green in color, that shoot straight upward) as early as possible.

        For SHD orchards, remove shoots within the protective carton and 8 in (20 cm) above the carton to maintain a single leader. Remove competing limbs as the leader approaches the top wire. When the leader is 12-18 in (30-46 cm) above the top wire, prune a handful of shoots, and tip 10-20 shoots along the sides of the tree to promote dense foliage and more fruitwood.

        Further training of trees depends on the method of harvest:

        • Trunk shaker. Prune to direct the growth into stiff upright scaffolds that transmit the force from the trunk shaking. Remove branches below a 45o angle from the vertical as they shake less efficiently. Remove branches extending laterally into the row middle, which reduce harvester efficiency.
        • Canopy-contact and over-the-row harvesters. Canopy contact harvesters remove olives with two different mechanisms. Some compress and agitate the canopy with a series of horizontal bars called bow rods that agitate the canopy with a vertical motion. Some have a head with vertical rows of radiating tines that extend into the canopy. The horizontal whipping motion at the tips of these tines against the vertical branches removes the olives. Both removal methods remove the fruit on the outer canopy more efficiently than interior fruit. Train the tree into an upright narrow canopy, with primary scaffolds parallel to the tree row and shorter branches extending into the row. Such training, achieved by hand pruning, mechanical pruning or both, will facilitate production of a continuous flat fruiting wall. Remove branches that extend into the row middle. These branches will interfere with harvester efficiency, can damage harvest equipment, and will probably be broken by the harvester.
  • Best Practices for Oil Processors

    These Best Practices for Olive Oil Processors are based on information presented at the Master Milling Short Course held each October at the UC Davis Olive Center. Our thanks to course presenters Leandro Ravetti, technical director, and Pablo Canamasas, lead miller, of Boundary Bend Ltd., Australia, for assisting in the development of these Best Practices.

    • Prior to Processing

      Choose the right olive varieties for the right growing conditions. Olives grown under irrigation in warmer climates allow the fruit to fully develop, which often leads to sweeter, milder oils. Olives grown under deficit irrigation in cooler climates tend to produce oils that are more robust, with more bitterness and pungency. Generally, it is challenging to grow cool-climate varieties in a desert climate or to produce a sweet and mild oil in a cool climate. In general, increasing irrigation will reduce bitterness and pungency, as will harvesting later in the season.

      Harvest healthy fruit. The best quality olive oil comes from healthy trees, with fruit that has not been damaged by pests such as olive fruit fly, diseases such as olive knot, or adverse environmental conditions such as drought and frost. To produce high-quality extra virgin olive oil, do not harvest fruit from the ground.

      Time the harvest for maximum quality and extraction. To achieve an optimal balance between oil quality and extraction efficiency, harvest the orchard as soon as the oil content has reached its maximum weight, and preferably when fruit moisture is between 50 and 55 percent. Measure oil and moisture content either with a near-infrared (NIR) instrument or by drying olives in a dehydrator or an oven. Collect and weigh a 100-olive sample from the area to be harvested. If using an oven, dry for one hour at 266 °F (130 °C), then turn the samples over and dry in the oven for an additional hour. Let cool and then weigh the olives again. Compare this weight to the fresh sample weight to determine moisture content. Calculate oil content by performing the same steps weekly as harvest time approaches, and harvest when the dry sample weight no longer increases over the previous week’s weight.

      Use the maturity index to estimate flavor profile when evaluating harvest timing. The maturity index provides information that may be useful in evaluating harvest timing to achieve a consistent style of oil from year to year. Greener fruit usually offer oils with typical green-fruit character (such as fresh-cut grass, leafy, green fruit, and herbaceous flavors) as well as elevated bitterness and pungency. Riper fruit generally provides ripe-fruit character (such as nutty, buttery and tropical flavors) with reduced bitterness and pungency. A small difference in fruit maturity can have a great influence on the fruity component of the oil, but it does not reliably correlate with oil accumulation or polyphenol content in the fruit.

      Choose an efficient harvest method that preserves quality. Choose harvest equipment that will minimize the amount of time that it takes for the fruit to get to the processing plant and that minimizes fruit damage. Shakers do not perform at a high rate of removal with green fruit, so the shaker may also need some manual assistance with tree-beating or hand-harvesting, or with the use of a loosening agent. Many mechanical harvesters can deliver fruit in good condition, with the exception of when laborers are beating trees with rakes and stepping on fruit on the tarps. The more the fruit is damaged the more critical it is that the fruit be processed quickly to achieve a high quality olive oil.

      Minimize foreign material in harvest containers. Keep leaves, rocks, twigs and other “material other than olives” (MOO) below 2.5 percent in harvest containers. Too much MOO usually means that there are problems in the orchard such as the fans on the harvest equipment not working correctly or the use of excessive levels of fruit-loosening agent in the orchard. Although equipment at the processing plant usually will remove much of the MOO, MOO can have a negative impact on the quality of the oil and may damage processing equipment. While adding leaves to the crusher can temporarily increase the green color and polyphenols of olive oil, the leaves also add an unpleasant off-flavor and astringency to the oil.

      Transport fruit quickly using appropriate containers. Post-harvest concerns include fruit damage, transport time, and the ambient temperature, as it is extremely important to avoid fruit fermentations. These factors are not very important if the fruit is processed within about four hours of harvest, but become critical when processing lags beyond four hours. The longer it takes to process the olives the more critical it will be to have less fruit damage, smaller-sized and well-aerated containers, and lower outside temperatures. The worst containers for olive transport are those that do not allow proper ventilation, particularly bags.

      Ensure that the fruit is properly cleaned before crushing. The fruit needs to undergo a cleaning process to eliminate the MOO and presence of dust. Cleaning systems blow away leaves, dust and other MOO using a fan. The fruit can then be washed if required, but washing may also reduce oil extractability and the level of polyphenols of the oil.

    • Best Practices when Processing

      Evaluate the fruit condition to decide how to process. Prior to crushing, evaluate maturity, moisture and variety of the fruit to determine the most appropriate strategy for paste preparation. The fruit condition will also determine if the operator should use processing aids such as talcum powder and enzymes to improve oil extractability and decanter working-capacity.

      Choose the correct grid size for proper crushing degree. Low-maturity fruit will characteristically require a fine crushing degree, and therefore a small grid size in the crusher, to maximize oil extractability. Riper fruit with softer cell tissues, as well as high-moisture fruit, are best prepared with larger grid sizes (6 - 7mm) to maximize extraction efficiency. De-pitting the olives prior to crushing can modify the aromatic profile and phenolic composition of the oil, however, this practice also reduces extraction efficiency.

      Adequately adjust the malaxation parameters. Keep malaxation times within 75 minutes to allow for a steady kneading of the paste and a slow release of the oil. Lower malaxation temperatures tend to generate more aromatic and complex oils but also reduce extraction efficiency. Conversely, higher malaxation times maximize paste extractability but reduce the complexity of the oil. Temperatures of 80 – 86 °F (27 – 30 °C) represent a good compromise in achieving high oil quality and extraction efficiency. Frequently inspect the paste in the malaxer to look for the presence of free oil being released from the paste. Malaxation with nitrogen blanketing or under vacuum can marginally improve oil quality.

      Consider the use of processing aids when required. Talcum powder and pectinase enzymes can help in improving the physical condition of the paste for a better oil extractability. Plan to add talcum powder to the paste in the malaxer if the fruit that will be processed is excessively wet (moisture > 58%) or if the paste looks emulsified in the malaxer. Also consider adding pectinase enzymes to the paste when the fruit is of low maturity (green or turning-color). These products usually have a synergetic action when used together and can be added at the same time in the malaxer.

      Adjust the decanter speed and monitor oil losses in the pomace. When processing the paste, ensure that the oil emerging from the decanter is not too “dirty” with paste as this could mean that the paste feeding-speed is excessively high or that the decanter plates are excessively open. In the case of a two-phase decanter, consider injecting up to 5 - 6% of water to reduce the chances of losing oil in the waste. Check the waste regularly to determine the extent of oil losses, as well as whether paste-preparation decisions were correct and whether to slow down the feeding rate of paste into the decanter.

      Continually inspect the condition of the oil coming out from the vertical centrifuge. Check the oil coming out of the vertical centrifuge to ensure that it appears clean with a milky aspect. If the oil has a shiny aspect it may mean that there are excessive temperatures in the malaxer, or that excessively warm water was added into the decanter or the vertical centrifuge. Visually ensure that the vertical centrifuge has no oil coming out from the water outlet, or water from the oil outlet. It is safe to add to the centrifuge a small amount of water with a similar temperature to the oil, or 2 – 4 °F higher, to improve the cleaning operation.

      Let the oil settle before storing. Allow the oil to rest in settling tanks to separate the oil from fine water droplets and particles in suspension. The settling process will also help release most of the air bubbles contained in the oil. Ensure that the settling tanks are drained regularly to remove sediments and water. After a minimum of 16 hours of settling, take a sample of the oil and, if possible, carry out an in-house sensory analysis as well as testing of free fatty acids and peroxide value. Based on this sensory and chemical analysis, decide on the final destination of the oil in the tank storage facility.

      Store the oil properly to maximize the shelf life of the product. Utilize stainless steel tanks, nitrogen blanketing and temperature control in the storage room to minimize oxidation processes in the oil. The oil is best kept at temperatures ranging between 59 °F and 66 °F (16 °C – 19 °C.) Ensure that the storage tanks are drained regularly to remove water and sediments to minimize hydrolytic reactions in the oil. Once the oil has fully settled (approximately 45 days after processing depending on room temperature), move the oil to a new clean tank to remove the “mud” normally stuck to the bottom of the tank. Finally, send oil samples to a laboratory for chemical and sensory testing to ensure that the oil complies with trade standards.

  • Olive oil tips for consumers

    Value freshness.
    Find a truly fresh extra virgin olive oil and compare with the familiar “olivey” flavor often mislabeled as extra virgin. A quality extra virgin olive oil should smell and taste fresh, have fruity notes (descriptors might include grassy, apple, green banana, artichoke and herbaceous), and may have bitterness and spiciness (which are indicators of healthy antioxidants.)

    Value freshness

    Insist on a harvest date.
    Better producers will indicate on the container when the olives were harvested. Look for the most recent harvest, which is typically November – December in the Northern Hemisphere and May - June in the Southern Hemisphere. A “best by” date often is two years from the time the bottle was filled, not when the olives were processed, and therefore is an unreliable indicator of quality.

    Insist on a harvest date

    Choose a good container.
    Heat and light are the enemies of freshness. Containers are made from dark glass, tin, or even clear glass largely covered by a label or placed in a box.

    Look for a quality seal.
    Producer organizations such as the California Olive Oil Council and the Australian Olive Association require olive oil to meet quality standards that are stricter than the minimal USDA standards. Other seals may not offer such assurance.

    COOC-revised-seal-2014.jpg
    Look for a quality seal

    Keep cool and dark. Exposure to heat and light will diminish freshness and shorten the shelf life of olive oil.

    Use it up. To enjoy extra virgin olive oil at its best, buy in a container size that that can be finished in about six weeks or so. Freshness will diminish with time.

  • Olive oil tips for professional buyers

    know the process
    Know the process
    Know the process.
    Evaluate whether processors observe minimal best practices:

    • Fresh, undamaged olives are processed as soon as possible after harvest.
    • The processing facility is clean and the equipment thoroughly washed daily.
    • Oil is settled for 24 to 48 hours prior to transfer to temperature-controlled stainless steel tanks for racking, storage and possible filtration.
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    Taste before buying

    Taste before buying.
    Evaluate different olive oils and choose those that will meet customer needs. Retain samples of the oils selected and compare to the oils delivered.

    Raise specifications.
    UC Davis studies show that olive oils usually pass the common chemistry standards (FFA, UV, PV) even when the oils are old and defective. Require the supplier to deliver only oil from the most recent harvest, to meet better chemical standards that have a higher correlation with flavor quality and freshness (DAGs and PPP) and insist upon an independent sensory panel analysis.

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    Test regularly

    Test regularly.
    A supplier’s certificate of analysis may not reflect whether the olive oil is old and defective. Choose a laboratory to conduct sensory panel, DAGs, PPP, FFA, UV, and PV tests to get an independent assessment of quality. Test oil upon delivery or randomly throughout the year.

    Store cool.
    Ideal warehouse storage temperature is 59 °F to 64 °F (15 °C to 18 °C). Warmer storage conditions will accelerate the deterioration and shorten the shelf life of the olive oil.

When:

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In this Section

These best practices concisely summarize key factors in growing and processing olives as well as in the purchasing of extra virgin olive oil.

UC Davis Olive Center

The UC Davis Olive Center is a self-funded university/industry coalition that seeks to do for olives what UC Davis did for wine.

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