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 (FDA) Avocado Surveillance Sampling Program.
- Foodborne illnesses associated with avocados are generally linked to processed avocados and avocado-containing products such as guacamole.
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
In recent years, multiple foodborne outbreaks and product recalls have been associated with avocados and avocado-containing products. Avocados are used in many different types of recipes with guacamole being an especially popular dish.
The Centers for Disease Control and Prevention (CDC) began conducting surveillance for foodborne disease outbreaks in 1973. However, it wasn’t until 1984 that a salsa or guacamole-associated (SGA) outbreak was reported. From 1984 to 1997, SGA outbreaks accounted for 1.5% of all food establishment outbreaks. This figure more than doubled to 3.9% from 1998 to 2008. Nearly one out of every 25 restaurant-associated foodborne outbreaks with identified food sources between 1998 and 2008 can be traced back to contaminated salsa or guacamole. According to the CDC Food Tool, from 1998 to 2014, there have been six outbreaks (94 illnesses) associated with avocados and 46 outbreaks (1,353 illnesses and 40 hospitalizations) associated with guacamole.
In 2014, 80 cases of whole avocados were recalled by Latin Specialties, Inc. of Houston, Texas due to positive test results for Salmonella. The producer of the avocados, Unity Groves Corp. of Homestead, Florida, initially sold the lot to Fresh King, which sold it to another entity that sold it to Latin Specialties, Inc. Routine testing of avocados by FDA identified the pathogen and no known lot codes were identified on the product. The source of contamination was unknown, due to improper chain of custody documentation.
In 2010, J. Hellman Frozen Foods Inc. of Los Angeles, California recalled 992 cases of Avocado Pulp that was distributed by Señor Mexicano. The recall involved 4,960 retail units distributed in California and Hawaii. A random sample of tests conducted by FDA was positive for Listeria monocytogenes. No illnesses were associated with this recall.
In 2011, two additional recalls were prompted due to positive Listeria monocytogenes results. Fine Mexican Food Products, Inc. of Ontario, Canada recalled 1,423 cases of Frozen Avocado Pulp and 1,820 cases of Avocado Halves. This recall was the result of multiple positive Listeria monocytogenes test results in the manufacturing facility in Peru. The second recall involved Fresh Food Concepts, Inc. of Buena Park, California. The company’s Layer Dip products contained avocado pulp that tested positive for Listeria monocytogenes as a result of the routine sampling program by the Food and Drug Administration (FDA). , Fresh Food Concepts, Inc. ceased the use of avocados from its supplier, which was not named. , No illnesses were associated with either of these recalls.
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 production and distribution of Avocados please visit the Produce Point of Origin Database.
Standard food safety practices should be followed when preparing avocados, including the “clean, separate, cook, and chill” guidelines recommended by the “Check Your Steps” campaign. Avocados that are used to make guacamole in a restaurant setting can pose a risk for foodborne illness for multiple reasons: the product may not be refrigerated appropriately and it is often made in large batches, so a small amount of contamination can affect many customers. Inappropriate storage times or temperatures were reported in 30% of SGA outbreaks in restaurants or delis, and food workers were reported as the source of contamination in 20% of the restaurant outbreaks from 1998 to 2008. In addition, fresh guacamole often contains diced raw produce that has previously been implicated in a foodborne illness outbreak, including hot peppers, tomatoes, and cilantro.
FDA Avocado Surveillance Sampling Program
Under the FDA Food Safety Modernization Act 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 in 2014. The goals of this surveillance program are to keep contaminated products from reaching consumers and to facilitate a greater understanding of hazards. FDA collected a statistically determined number of samples of targeted foods over a relatively short period of time. From May 2014 to May 2015, FDA focused on sprouts, whole fresh avocados, and raw milk cheese (ages 60 days), collected more than 800 samples total, and tested for Salmonella, Listeria monocytogenes, and E. coli O157:H7. Data from this sampling assignment has yet to be released.
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 information on how to keep avocados fresh and stored properly check out 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.