Carrots

carrots
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Key Factsexternally-reviewed

  • Carrots are low-acid vegetables and therefore at higher risk of producing botulinum toxin when canned improperly.
  • Carrot producers should be familiar with the growing and harvesting processes that can expose carrots to contamination harmful to humans. These can include: land use history, fertilizer use, irrigation, field sanitation, field containers, and pesticide usage.
  • Carrots are grown in all 50 states, however California, Michigan, and Texas are the top commercial producers. Over 80% of all carrots produced in the United States are grown in California.
  • Per capita consumption of carrots has increased in the last 20 years, due in part to the popularity of ‘baby carrots.’
  • Proper washing, storage, and preservation methods are especially important with carrots since they are root vegetables with a neutral pH and relatively long shelf life.

Introduction

Carrots in a variety of colors.
Carrots in a variety of colors.

Carrots (Daucus carota) are root vegetables in the parsley family and relatives of poison hemlock. Coloration varies from yellow to purple, but the most common color is bright orange. This pigmentation is due to β-carotene, the provitamin form of vitamin A. In selecting for brighter color, the vitamin A content of common carrot varieties has increased over time. When ingested, β-carotene is converted to the active form of vitamin A, which is then bioavailable. Vitamin A is important for immune system functioning and healthy cell growth. Carrots are biennial, which means that the biological lifecycle is two years/seasons long. Flowers and seeds are produced in the second year. Originally, ‘baby-cut’ or cocktail carrots were made from imperfect larger carrots but now specially bred carrots are used which contain more sugar, and have a crispier texture and brighter coloration.

Foodborne Outbreaks

Several foodborne illness outbreaks have been associated with carrots. In 2004, an outbreak of Yersinia pseudotuberculosis O:1 was linked to raw carrots in Finland, affecting more than 400 school children. Symptoms of the illness are fever and acute abdominal pain, which can be similar to appendicitis pain.

Also in 2004, an outbreak of Shigella sonnei affected 47 air travelers who departed from Hawaii and raw carrots were identified as the likely vehicles of infection.

An international outbreak of botulism was attributed to carrot juice in 2008, likely caused by improper processing and refrigeration. Botulinum toxin A was found to be in both serum and stool samples of those infected. Carrots are low-acid vegetables so the juice is conducive to the production of botulism toxin.

Cyclosporiasis is another concern, and has resulted in several outbreaks. One case, in particular, was linked to a salad mix which contained carrots. Cyclosporaisis is an intestinal infection caused by a single-celled parasite, Cyclospora cayetanesis. It is essential to wash carrots and other produce because of any potential oocyte-containing matter left on the outside of the produce. Whole peeled and grated carrots were implicated in an outbreak of cryptosporidiosis in Denmark in 2005 affecting 99 people, Cryptosporidium hominis was identified as the cause of the outbreak.

There have also been outbreaks associated with improper canning of vegetables, including carrots. During 2008 and 2009, the most common cause of botulism outbreaks was home-canned vegetables. Between the years of 1999-2008, there were 116 outbreaks of foodborne botulism reported, and 38% were attributed to home-canned vegetables.

Production

Soil Preparation

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Carrots ready for harvest.

Carrots are most often grown in sandy loam or silt loam soil, to promote optimum water holding and drainage., Planting on raised beds can further aid in proper water drainage. Carrots need soil with adequate air and water drainage, since wet and compacted soils can cause deformed growth. Soil temperature, three inches below the surface, should be 50° F or lower. Carrots tend to thrive in light, sandy soil with neutral pH and full sun exposure, as opposed to very clay-like or wet, chalky soil. Carrots are a hardy crop that can withstand pH levels ranging from 5.5 to 8.0, but prefer soil that is overall more neutral. Before seeding, the soil should be tilled to loosen up compacted ground. For optimum root development and growth, carrots should have approximately 18-24 inches of well tilled soil that drains well. The presence of pebbles and stones in the soil can cause forked or misshapen carrots roots that are unmarketable.   Other factors that can cause stubbed or forked roots include pythium root dieback, nematodes, and exposure to frost.

Since carrots are a deep rooting crop, they are able to effectively extract nutrients from the soil. Soil tests should be utilized before planting and throughout crop development to measure soil nutrients such as nitrogen, phosphorous, magnesium, sulfur, boron, manganese, and potassium. If needed, nutrients can be applied prior to seeding and during crop maturation using sidedressing or broadcasting.  Carrots are sprinkler irrigated, so most materials including fungicides, fertilizers, etc are chemigated through sprinkler systems. It is important to be conservative when adding supplemental amounts of nitrogen. Excessive soil nitrogen can result in root cracking during harvest. Adding fresh manure to the soil is not recommended, due to food safety concerns and high nitrogen content.

Planting and Irrigation

In nature, carrots are biennial plants and require two growing seasons to complete their life cycle culminating in seed production. However, for mature root production, commercial carrots are grown as an annual crop yield. Carrot crops grow optimally in environments with moderately cool days (60-75° F) and colder night (45-50° F). Too high of temperatures can cause bolting, discoloration, and woodiness, making the carrot yield less marketable. Carrots are always direct seeded and can be planted in both the spring and summer.  The pounds per acre seeding rate varies between raw and coated seeds. High density seedings are often utilized in carrot production.  One potential benefit of high density seeding is an overall higher yield. However, the decrease in airflow and soil space can negatively impact the size of the carrots and increase the risk of crop disease. The planting density of carrots is dependent on the crop use.  Fresh market carrots are planted at 900,000 seeds per acre, whereas baby carrots are planted at 1.5-1.9 million seeds to acre.  Processing carrots are planted at a fraction of that seed density. The ideal seeding depth is 1/8 “– 1/4”, but should not exceed 1/2”.,

Maintaining soil moisture is most critical during germination due to the fact the seed is planted so shallow. Moisture stress can result in a higher percentage of cull carrots that are too twisted, knobby, or bent to process or sell in the fresh market. Moisture stress can also hinder sugar set and negatively affect the overall taste. Although average watering volumes differ across the United States, approximately 24”-30” of water is consumed by the crop during the growing season.  Sprinkler systems should be able to deliver at least an inch of water within a couple hours, but should be slow enough in delivery to aid in absorption and prevent run-off. Efficient sprinkler systems can also be used to apply fertilizer when necessary. In addition to watering, weeding is crucial to the proper health and development of carrot crops. Weeds not only compete for light, water, soil nutrients, and growth space, but can also harbor insects, pathogens, and diseases that are harmful to carrot crops.

Pests of Concern:

Carrots are resistant to pests and diseases that affect other crops. Cavity Spot and nematodes are the main pests of concern. In addition, flea beetles, Aster Yellow Disease, and wireworms can cause problems, but are minor in relation to Cavity Spot and nematodes. Several strategies may be employed to avoid flea beetles, including delaying planting by a few weeks in the spring, tilling the garden in the fall to bring them to the surface, and utilizing homemade sprays made from rubbing alcohol, water, and liquid soap.

To protect against Aster Yellow Disease, weeds need to be controlled. Regarding wireworms, soil should be tested in the fall, prior to the first frost. Prevention of wireworms is important since no insecticide is currently available to control wireworms once the crop is planted.

Carrots with Aster Yellow Disease
Carrots with Aster Yellow Disease

Harvesting and Handling

Carrots are ready for harvest anywhere between 85-135 days after planting. The prime harvesting period for processed carrots is from September 15-October 15. Fresh market carrot harvest can occur from late July to September, or late into October. Ideally, carrots should be harvested before reaching full maturity. Commercially grown carrots are harvested mechanically using self-propelled multi-row harvesters. Carrot have their tops removed in the field, are loaded into trucks, and transported to sheds for washing, grading, sizing, and packing. Chlorine concentrations of 100-200 ppm have been recommended for washing carrots in commercial operations with subsequent potable water rinsing to remove any excess chlorine before being packaged or prepared for markets. Many farmers selling locally at farmers’ markets are reluctant to use such high levels of chlorine and may only rinse with tap water.

For commercial holding/storage, carrots should be held at 32°F in 98-100% humidity with good airflow., Carrots in these conditions can be stored for up to 7 months. Proper storage is necessary to reduce the risk of postharvest decay such as gray mold rot, watery soft rot, Rhizopus rot, bacterial soft rot, and sour rot. Carrots can be stored with a variety of vegetable products, however, they should not be stored with crops that produce ethylene (ie – bananas, apples, melons, peaches, and other fruits). Carrot sizing and grading determines whether carrots are sold in fresh market, for processing, or as culls.

Food Safety

Food safety for carrot crops from field to fork is extremely important, especially since a large portion of carrots are consumed raw.  The UGA Extension, Commercial Production and Management of Carrots handbook notes that, “carrot quality and safety are often perceived by consumers to mean the same thing“. Although high quality carrots might have good physical appearance and taste, the potential pathogens and toxins on its surface can go unnoticed. There are a variety of steps in carrot crop growth and production that can expose the vegetable to contamination.  Some of these include:

  • Land Use History: Growing carrot crops on or near land where animals had been grazing where pathogenic bacteria in the soil can be transferred to humans.
  • Fertilizer Use: Fertilizers that have been composted improperly can contain pathogenic bacteria.
  • Irrigation: When using natural surface water from ponds, lakes, etc., it is possible that the water source can be contaminated and harbor pathogenic bacteria.
  • Hand Harvesting: Harvesting by hand can increase the risk of transferring fecal and bacterial contamination from field workers to the crop.
  • Field Containers: The containers used to hold carrots after harvesting should be non-toxic, free of dangerous materials (wood, nails, splinters, etc), and able to be cleaned and sanitized.  Containers can be sanitized using a strong sodium hypochlorite solution applied from a high-pressure sprayer.
  • Pesticide Use: Use of illegal pesticides or improper application of pesticides can cause harmful residue contamination on the crop.

Carrots should be stored at refrigerator temperatures, generally between 32-35°F, but certainly at 40°F or below. Storage in a closed plastic bag will help limit moisture lost and maximize preservation. It is also important to refrigerate carrot juice to protect against the production of botulism toxin. Proper home canning procedures are critical since carrots are a low acid vegetable. Before use, carrots should always be washed well and scrubbed with a vegetable brush. Peeling followed by rinsing is recommended for removing possible surface contamination. Following proper handling methods is imperative with home food preservation of carrots. The process should begin with washing, peeling, and then rewashing the carrots.  Recommended pressure levels and processing times must always be followed when canning carrots.

Consumer handling recommendations include washing carrots under running water and scrubbing with a clean vegetable brush.  Peeling carrots can help in removing the tough to clean outer layer.

Home canned carrots.
Home canned carrots.

Consumption

In 2010, Americans consumed an average of 9.8 pounds of carrots per person. Of the total weight consumed, 7.6 pounds were fresh carrots and 2.2 pounds were processed (canned, frozen, etc). In the 2006-2007 Population Survey Atlas of Exposures, 52.4% of the survey cohort reported eating mini-carrots from a sealed bag within the past 7 days. In contrast, only 29.9% of the survey cohort reported consuming full size loose or bagged carrots within the past 7 days.

Reports by the USDA Economic Research Service have noted different carrot consumption patterns across regions in the United States.  In the West, Central, and Eastern regions of the United States, they did not find significant differences between fresh, at-home carrot consumption. However, in the Southern region they found that consumers, on average, ate 2 pounds less than consumers in the other three regions. Furthermore, the 1998-2003 ACNielsen panel data showed that Non-Hispanic Whites and Asians had the highest at-home carrot consumption. Due to changes and growth in the population, updates to the ACNielsen panel data would be beneficial to represent current demographics and consumer trends in the United States.

Nutrition

Carrots are a versatile vegetable readily available fresh, frozen, or canned. In fact, they were the first vegetable to be canned commercially. They are one of the richest sources of vitamin A and an excellent source of antioxidants. Carrots are fat free, low in sodium, cholesterol free, a good source of vitamin C, and low in calories.

References

Externally Reviewed by: Joe Nunez, MS
Affiliation: UC Cooperative Extension Farm Advisor
Reviewed on: 28 August 2015

Externally Reviewed by: Mike Bartolo, PhD
Affiliation: CSU Department of Horticulture and Landscape Architecture, Vegetable Crop      Senior Research Scientist and Extension Specialist
Reviewed on: 3 November 2015

Authors

Hannah Pensack-Rinehart

Hannah Pensack-Rinehart

Hannah Pensack-Rinehart, Colorado School of Public Health MPH student

Marisa Bunning

Marisa Bunning