- Avocado trees are native to the humid, sub-tropical and tropical regions of central and northern South America. They never go dormant.
- Nearly 90% of avocado production in the United States takes place in California.
- Avocados are harvested by hand and start to ripen once they are picked from the tree.
- Commercial food safety practices for avocados have recently been strengthened due to the Food and Drug Administration’s (FDA) microbiological surveillance sampling of avocados and select avocado products.
- Between 1998 and 2017, at least 8 avocado-associated outbreaks were reported to CDC’s National Outbreak Reporting System (NORS), causing 156 illnesses, 7 hospitalizations, and no deaths.
- Pathogens associated with avocado outbreaks and recalls include Salmonella and Listeria monocytogenes.
The avocado tree (Persea americana) is a tropical evergreen tree with three horticultural races: Guatemalan, Mexican, and West Indian. Trees can reach up to 60 feet (18 meters) tall and grow throughout the year; they do not enter a dormant state. The timing and length for each crop cycle depends mostly on temperature so crop development dates vary by location and from year to year.
The avocado was first domesticated in the United States by Henry Perrine in 1833 in Florida. There are more than 56 types of Florida avocados which are classified into three categories: summer, fall, and winter. The summer fruit has a bright green, smooth, thin skin whereas the fall and winter varieties are also bright green but have thicker, rough textured skins. The Hass avocado was discovered in La Habra Heights, California in the 1920s by Rudolph Hass. At first, the Hass avocado was not widely accepted among consumers because of its dark skin color. However, it is now the most widely-consumed type of avocado produced in the U.S. In 1957, Hass avocados only comprised 15% of the total crop yield. By the end of the 2010-2011 crop years, Hass avocados comprised 94.5% of the avocados commercially grown in California.
Avocados come in a variety of shapes, sizes, and colors. They can be shaped like a ball, a teardrop, or a football. Depending on the variety, the interior flesh ranges from bright yellow to yellow-green to pale yellow. Although the shapes and colors vary, all avocados have a smooth, creamy flesh and a delicate nutty flavor.
Foodborne Outbreaks and Recalls
Between 1998 and 2017, at least 8 avocado-associated outbreaks were reported to CDC’s National Outbreak Reporting System (NORS), causing 156 illnesses, 7 hospitalizations, and no deaths. In outbreaks with known etiology, the most commonly implicated pathogens were Salmonella (50%) and norovirus (33%), but have also included Bacillus cereus (17%).
There have also been avocado and avocado product recalls without any reported illnesses. Such voluntary recalls have been due to potential contamination with Salmonella and Listeria.
Below are examples of outbreaks and recalls associated with avocados reflecting the diversity of vehicles, pathogens, and other circumstances:
In 2010, J. Hellman Frozen Foods Inc. of California voluntarily recalled their Mexicano brand Avocado Pulp after random testing by the FDA yielded Listeria monocytogenes. There were no reported illnesses.
In 2011, Fine Mexican Food Products of California voluntarily recalled their frozen avocado pulp and IQF avocado halves after avocado pulp that had been manufactured in the same facility in Peru tested positive for Listeria monocytogenes. There were no reported illnesses.
In 2011, Fresh Food Concepts, Inc. of California voluntarily recalled their Layer Dip products after testing by the FDA revealed that the imported avocado pulp used in the dips contained Listeria monocytogenes. There were no reported illnesses.
In 2014, Latin Specialties, Inc. of Houston voluntarily recalled their whole avocados after testing by the FDA yielded Salmonella. The avocados originated from Unity Groves Corp. of Florida, but had gone through multiple entities, including Fresh King, before receipt by Latin Specialties, Inc. There were no reported illnesses.
In 2019, Henry Avocado Corporation voluntarily recalled their California-grown conventional and organic whole avocados after environmental samples tested positive for Listeria monocytogenes during routine inspection. There were no reported illnesses.
In 2019, Nature’s Touch Frozen Foods (West) Inc. voluntarily recalled their Signature Select brand frozen avocado chunks after routine product sampling by the FDA yielded Listeria monocytogenes. There were no reported illnesses.
The United States is the second largest producer of avocados after Mexico. About 90% of avocado production in the United States takes place in California by more than 5,000 growers. The average grove size in California is about 13 acres. One avocado tree can produce from 200 to 500 avocados per year. About 400 million pounds of avocados are harvested each year in California alone. Florida and Hawaii produce most of the remaining 10% of avocados produced in the United States. In Florida, there are over 6,500 production acres in Miami-Dade County and a small amount of acreage in Collier County, where the climate is conducive to cultivating tropical fruits. Dooryard avocado trees make up an estimated 10% of the canopy in Miami-Dade County. The avocado industry in Florida is estimated to produce more than $55 million annually and supports over 1,000 full-time and part-time jobs.
Worldwide avocado production has dramatically increased from 4.6 billion pounds in 1994 to 6.8 billion pounds in 2004.
In Florida, the common practice is to plant 87 trees per acre (planted 20 feet apart), but newer orchards are increasing the density to 100 trees per acre (planted 18 feet apart). New orchards are usually planted on existing agricultural land that was previously used for agricultural production. The sandy and limestone soils can produce satisfactory yields, ranging between 11,000 and 19,500 pounds per acre.
Avocado trees do not require extensive pruning, especially in their younger years. Most pruning takes place every other year and involves removing dead branches from the top of the canopy and maintaining desired width. Trees are kept at or below 20 feet high so they do not topple over from high winds.
Avocado trees to do not search for water, as their roots are shallow in the soil. The top layers of the soil can dry out quickly, and trees do not tolerate flooding, so proper irrigation is a critical part of cultivation. Continuously wet or flooded conditions can result in decreased growth, decreased crop yield, nutrient deficiency, and root infection by Phytophthora fungi, and sometimes tree death.
The frequency of irrigation depends on weather, rainfall, variety planted, type of soil, and season of the year. High-volume irrigation with micro-sprinklers is the most common irrigation system in Florida because it serves as under-tree freeze protection. Regular irrigation is vital to fruit production and survival, specifically in California where the climate is semiarid. California groves are irrigated by sprinklers, micro-sprinklers, or drip systems. In Florida, a general rule of thumb is to irrigate one inch of water per week.
Avocado flowers (petals, stigmas, and anthers) are modified shoots and leaves. Flower buds begin to grow during late summer or fall and continue to develop through winter. Blossoming and fruit set occur from late winter through early summer, but most fruits that are harvested develop from flowers that were pollinated in spring. Avocado flowers are about 2/5 inch wide (1 cm) and occur in groups of about 4 to 10 inches. A mature avocado tree can yield thousands of flowers per year. The flower contains both female and male parts. Once matured, the female part opens first and the male parts open the following day. Due to the large number of flowers in a relatively small area, the avocado tree is prone to genetic variability. Domesticated honey bees (Apis mellifera) are the most economically important avocado pollinators; most growers usually keep honey bee hives in their avocado groves to increase pollination and fruit yield. From pollination to maturity, avocados take at least six to seven months to mature. Mature fruits can stay on the tree for months without ripening; avocados do not ripen until after they are picked from the tree.
In order for avocado trees to produce fruit, they require sugars, hormones, and mineral nutrients. The type and amount of fertilizer applied depends mainly on the type of soil and age of the tree. In Florida, a 6-6-6 formulation is applied six times a year during the first two years of establishment at a rate of one pound per tree. An 8-3-9 formulation is applied six times a year during the third to sixth years at a rate of two to three pounds per tree. The amount of fertilizer applied increases with the age of the trees. Soils in south Florida are very alkaline (pH above 6.5), which inhibits the absorption of micronutrients. The most common micro-nutrient applied every year in most avocado orchards is iron, which is applied once or twice a year in a chelated form. A multi-nutrient, micro-nutrient blend, such as Keyplex, is also applied as part of the annual fertilization plan.
Since fruit can stay on the tree for long periods of time without ripening, harvesting may easily overlap from year to year. Harvest can begin in the late fall or early winter and may continue until the following fall. Avocados are harvested by hand; pickers work from the ground, use ladders, or remove the fruit using a pole equipped with a pull-cord operated terminal blade and fruit catching bag. In Florida, avocados are harvested from late May through March. A professional picker can pluck about 3,600 avocados a day using the specially equipped pole. When the fruit is picked off the tree, it is not ripe. As soon as it is picked, the ripening process begins.
In advanced commercial processing plants, once avocados are transported from the field to the factory, they are brought up by conveyer belt where they are graded and sorted. There are three grades of avocado.
- “U.S. No. 1” consists of avocados of similar varietal characteristics which are mature but not overripe, well-formed, clean, well-colored, well-trimmed and which are free from decay, anthracnose, and freezing injury, and are free from damage caused by bruises, cuts or other skin breaks, pulled stems, russeting or similar discoloration, scars or scab, sunburn, sunscald or sprayburn, cercospora spot, other disease, insects, or other means. Since these fruits are visibly appealing, they are usually shipped to grocery stores and displayed on shelves.
- “U.S. No. 2” consists of avocados of similar varietal characteristics which are mature but not overripe, fairly well-formed, clean, fairly well-colored, well-trimmed and which are free from decay and freezing injury and are free from serious damage caused by anthracnose, bruises, cuts or other skin breaks, pulled stems, russeting or similar discoloration, scars or scab, sunburn, sunscald or sprayburn, cercospora spot, other disease, insects, or other means. These fruits are not as nice in appearance as U.S. No. 1 fruits, but still taste the same. They are usually shipped to food service establishments and other retail settings for ingredients in food products, such as guacamole.
- “U.S. No. 3” consists of avocados of similar varietal characteristics which are mature but not overripe, which are not badly misshapen, and which are free from decay and are free from serious damage caused by anthracnose and are free from very serious damage caused by freezing injury, bruises, cuts or other skin breaks, pulled stems, russeting or similar discoloration, scars or scab, sunburn, sunscald or sprayburn, cercospora spot, other disease, insects, dirt or other means. Sometimes the damage does not allow these fruits to ripen correctly, so they are often used as animal feed.
During peak production, processing facilities can produce about 500,000 pounds of avocado per day. Once the avocados are sorted, the U.S. No. 1s are shipped off to grocery stores and some restaurants while they slowly ripen on their journey.
Florida avocados ripen best at temperatures of 60° to 75°F (16° to 24°C). At higher temperatures, fruit ripen unevenly and develop off-flavors. The lowest safe storage temperatures before fruit ripen is 55°F (13°C) for West Indian and 40° F (4°C) for most other Florida varieties. Chilling injury is characterized by a browning or darkening of the skin and/or grayish-brown discoloration of the flesh. After fruit ripen, they may be stored in the refrigerator.
U.S. No. 2s will most likely be used to make guacamole, so they are flash-ripened before they are shipped to their final destination. Pressurized, forced-air ripening rooms are specifically designed to ripen avocados at a faster rate. The ambient temperature is increased and about 100 parts per million of ethylene is pumped into the room. Ethylene is a naturally occurring ripening hormone that is artificially used in avocado processing facilities to speed up the process. The avocados in the ripening chamber become ripe in three days as opposed to seven or eight days. When the process is complete, the room is circulated with cold air to shock the fruit and prevent further ripening. After this step, the fruit are checked to ensure that they are at the desired ripeness. They leave the ripening room on a conveyer belt and pass under a machine that shoots a blast of ultrasound waves through each avocado. The machine tells the computer how ripe each avocado is. Avocados that are over or under ripened are shot off the line. At full speed, each sensor can process up to six avocados per second. The avocados that are ready for shipment are packaged by hand and shipped off to their destination.
For more information regarding the movement of avocados in the U.S., please visit the Produce Point of Origin Database.
Avocados are favorable to the growth of bacteria, as they have a high lipid and moisture content, are low in carbohydrates, and have a non-acidic pH level. Additionally, avocados and avocado products are often consumed raw and without a ‘kill step’ prior to consumption. Fresh cut avocado products carry an additional risk, as piercing the avocado’s skin may allow for the spread and growth of any pathogens potentially present on the exterior. Particularly in restaurant settings, foods like guacamole may present a foodborne risk due to improper storage or food worker handling, the practice of preparing large batches, and inclusion of other raw ingredients previously implicated in foodborne outbreaks, such as cilantro, tomatoes, onions, and hot peppers. From 1984-2008, guacamole was the potential vehicle in 35 outbreaks reported to the Center for Disease Control and Prevention’s Foodborne Disease Outbreak Surveillance System. The most commonly reported pathogens were Salmonella, Shigella, and norovirus, but also included Clostridium perfringens, Escherichia coli, Bacillus cereus, Staphylococcus, Campylobacter, hepatitis A virus, and chemical agents.
Consumers should thoroughly wash avocados under running water before eating, cutting, or cooking, even if the skin will be removed prior to consumption. Promptly consuming fresh avocado after cutting and discarding the avocado skin may further reduce the risk of illness. Consumers should also follow the standard “clean, separate, cook, and chill” food safety practices.
Under the Food Safety Modernization Act (FSMA) and as a part of the FDA’s risk-based and preventative approach to food safety, the agency developed a new, more robust microbiological surveillance sampling approach. This approach aims to collect many samples of targeted foods over a short period of time to determine any common factors among positive microbiological findings. Avocados were selected for sampling in part due to a CDC study’s finding that Salmonella contaminated salsa or guacamole resulted in 26 outbreaks from 1973-2008. This study also found that contaminated salsa or guacamole accounted for nearly 1 in every 25 restaurant-associated outbreaks with an identified vehicle from 1998-2008, accounting for nearly 3.9% of all food establishment outbreaks.
From 2014-2016, the FDA collected and tested both imported and domestic whole fresh avocado samples to determine the prevalence of Salmonella and Listeria. Avocado pulp samples were also collected and tested for Listeria. The prevalence of Salmonella and Listeria on the skins of whole fresh avocados were 0.74% and 17.73%, respectively. The prevalence of Listeria in avocado pulp was 0.24%. From 2017-2019, the FDA collected and tested both imported and domestic processed avocados and guacamole samples to determine the prevalence of Salmonella and Listeria. Final results of this sampling are pending.
Avocado consumption in the United States has doubled over the past 10 years and is now about four times higher than consumption in the mid-1990s. Avocados have become more abundant in the U.S. due to a large increase in avocado imports. From 2012-2015, U.S. net production accounted for about 20% of U.S. consumption, compared to about 80% of U.S. consumption in the 1990s.
The Hass Avocado Board (HAB) is an agricultural promotion group established in 2002 to promote the consumption of Hass avocados in the U.S. A 12-member board representing domestic producers and importers of Hass Avocados directs HAB’s promotion, research, and information programs under the supervision of the United States Department of Agriculture (USDA). Funding for HAB comes from Hass avocado producers and importers in the U.S.
For more information on the shelf life of avocados, please visit the FoodKeeper App.
Avocados are considered a superfood. They are nutrient dense, contain relatively few calories, and provide a substantial amount of vitamins, minerals, and other nutrients. One-fifth of a medium-sized avocado (1 ounce) has 50 calories and nearly 20 vitamins, minerals, and phytonutrients, including 4% of the recommended Daily Value (DV) for vitamin E, 4% vitamin C, 6% folate, 8% fiber, 2% iron, 4% potassium, with 81 micrograms of lutein and 19 micrograms of beta-carotene. The 2010 Dietary Guidelines for Americans recommends that Americans increase their intake of dietary fiber and states that dietary fiber that occurs naturally in foods may help reduce the risk of cardiovascular disease, obesity, and type 2 diabetes, as well as help provide a feeling of fullness and promote healthy laxation. One-fifth of a medium California avocado (1 ounce) provides 8% of the Daily Value for fiber, while enjoying one-half of a medium California avocado provides 20% of the Daily Value for fiber. Avocados can act as a “nutrient booster” by enabling the body to absorb more fat-soluble nutrients, such as vitamins A, D, E, and K, in foods that are eaten with the fruit.
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