- Kale is a member of the Brassica family, which includes mustards, turnips, and cabbage. It is considered a leafy green, along with lettuce, swiss chard, and spinach.
- Kale is related to primitive cabbage dating back thousands of years to the Mediterranean and Asia Minor regions; its leaves tend to be narrow and curly in appearance.
- Kale is a cool-season crop that thrives in the spring and fall and is capable of tolerating frosts and light freezes. These greens contain a wide variety of nutrients, with a single cup of kale delivering over 500% of the daily value of vitamin K.
- Between 1998 and 2018, at least 4 kale-associated outbreaks were reported to CDC’s National Outbreak Reporting System (NORS), causing 19 illnesses, 5 hospitalizations, and 0 death, which gave these types of crops a reputation as risky food choices.
- The leading pathogens for leafy greens are Listeria monocytogenes, Shiga-toxin producing Escherichia coli, and Salmonella.
The cultivated kale of today is related to wild, primitive cabbages dating back over 2000 years to the Mediterranean and the Asia Minor regions. It arrived in Europe and the Americas through various trade routes. It is from the Acephala (meaning without a head) variety of the Brassica family and is derived from borecole. Kale is a Scottish word that comes from “cole” or “caulis” meaning whole cabbage plant. It is a biennial crop that is easy to grow.
Kale is a popular vegetable found on many grocery store shelves, either bunched or prepackaged for the consumer. Until recently, kale has been used primarily as a garnish, but today it is a major nutrition staple used in salad mixes or as a standalone ingredient. It ranges in color from dark green to purple. There are three major varieties of kale: Curly, (also known as Scotch), Toscono, and Siberian. Curly kale is the most widely sold and consumed variety and has dark, green leaves with frilly edges and a coarse texture. Toscano kale, also known as dinosaur kale, is an heirloom variety with a dark, blackish color and is popular with many direct market outlets. Siberian kale has tender, blue-green leaves with ruffled edges. It has the mildest flavor of the three varieties. Although kale is predominately grown in California and Georgia, it thrives in almost any environment where there is a cool fall growing season. In fact, a light frost has been known to enhance the sweetness of this green. Kale is an easy vegetable to incorporate into the local food system because of its versatility, popularity, and health benefits.
Food Outbreaks and Recalls
As with all leafy greens, kale is susceptible to contamination by foodborne pathogens and has been associated with outbreaks of Listeria monocytogenes and Salmonella species. Most of the outbreaks and subsequent recalls thus far have involved prepackaged salad or vegetable mixes, which often include kale.
In 2015, Dole Fresh Vegetables, Inc.’s prepackaged salad mixes sickened 19 individuals with Listeria monocytogenes across 9 states, causing 19 hospitalizations and no deaths. Routine product sampling of Dole brand Field Greens packaged salad obtained from a retail location in Ohio yielded a Listeria isolate genetically similar to patient isolates and prompted a halt of production and voluntary recall of all packaged salads produced at Dole’s processing facility in Springfield, Ohio. Implicated packaged salads, including President’s Choice brand Baby Kale, Dole brand Kale Caesar Salad Kits, Dole brand Sweet Kale Salad Kits, and various mixes, were packaged under multiple brand names and distributed throughout the U.S. and five provinces in eastern Canada. The Public Health Agency of Canada also reported illnesses.
In 2016, Pacific Coast Fruit Company’s Taylor Farms brand Organic Kale Medley Power Greens Mix sickened 6 individuals in Minnesota with Salmonella enteritidis, causing one hospitalization and no deaths. The implicated product was purchased from Sam’s Club retailers located in Minnesota and the product was promptly removed from shelves. Pacific Coast Fruit company also issued a voluntary recall. World Class Distribution Kitchen, LLC also voluntarily recalled Trader Joe’s brand Kale & Edamame Salad sold throughout the Midwest as a precautionary measure, due to possible Salmonella contamination
In 2016, Osage Gardens Inc.’s Organic 2-ounce Micro Greens were voluntarily recalled as a precautionary measure due to potential Salmonella contamination. Routine FDA testing of finished product yielded Salmonella and prompted the recall and temporary production cessation. Implicated products were distributed to Whole Foods stores in Colorado and Kansas. The Micro Greens product includes a mixture of kales, collards, mustards, beets, amaranth, herbs, and other greens. No illnesses were reported.
In 2016, CRF Frozen Foods’ frozen vegetable and fruit products sickened 9 individuals with Listeria monocytogenes across 4 states, causing 9 hospitalizations and 3 deaths. CRF issued a voluntary recall, which was later expanded, of frozen vegetable and fruit products produced at its processing facility in Pasco, Washington. The recall included more than 350 products sold under 42 brand names, as well as at least 100 other products prepared by other companies using CRF ingredients. Implicated products, including Bybee’s brand Organic Chopped Kale, Organic by Nature brand Organic Chopped Kale, O Organics brand Chopped Kale, and Wild Oats brand Organic Chopped Kale, were distributed throughout the U.S. and in Canada.
In 2017, CC Kitchens salad and slaw kits were voluntarily recalled as a precautionary measure after environmental testing at a leafy greens processor yielded Listeria monocytogenes. No contamination of product or illnesses were reported.
In 2017, Mann Packing’s minimally processed vegetable products were recalled as a precautionary measure after random sampling of product yielded Listeria monocytogenes. Potentially contaminated products were distributed to multiple retailers and produce companies that distribute products under multiple brand names throughout the U.S. and Canada. Some recalled products included Mann brand Kale Beet Blend, Mann brand Nourish Bowls Butternut Kale Risotto, Western Family brand Spicy Southwestern Kale Kits, Western Family brand Kale Salad Kits, and Western Family brand Kale Caesar Salad Kits. No illnesses were reported.
The majority of kale is grown domestically in California and Georgia, and a large portion of kale production is certified organic. From 2007 to 2012, the number of farms reporting growing kale more than doubled from 1,000 to 2,500, with 1,680 acres having been harvested in California. Kale is an easy crop to grow and integrate into a farming system due to its resistance to most pests (it is susceptible to a few common pests, such as black diamond moth) and diseases, as well as its ability to thrive in cool environments. Farmers’ markets also play a role in the success of kale and other leafy greens due to season-extending techniques such as cultivation using hoop houses (also known as polytunnels), which create a longer market season.
Please find more information on kale production on the Produce Point of Origin Database.
Kale prefers the cooler temperatures typical during the spring and fall months. Kale flavor is enhanced by cool temperatures because sugar content increases, improving the taste of the leaves.
Kale grows best in a fertile, well-drained loam soil with a deep, fine to medium texture. A pH between 6.0 and 7.5 is ideal for a thriving kale plant. Leafy greens like kale tend to have shallow roots, which helps them grow faster and produce continuously throughout the season. Kale can be direct seeded in a farming system at a depth of 0.25 inches and later spaced from 1 to 2 inches for optimal growth. Alternately, it can be transplanted. Removing outer leaves throughout the crop’s lifespan is important to continue to encourage leaf growth. Germination for this crop generally occurs seven to ten days after being planted. Once the plants have grown three inches, be thin, if needed, to ensure a ten-inch space in between. Kale generally requires 12 to 14 inches of water during the growing season. It is important for the health of the plant that irrigating procedures are performed uniformly. Kale does not do well if the plant is over watered, but it does need consistent moisture from regular watering.
Kale is ready to harvest between 50 to 90 days after growth, depending on whether it was transplanted, and typically yielding five to six tons (350 or 400 cartons) of product in the first harvest. The best way to tell if kale is ready for harvest is by checking the leaf color: a rich, green leaf a with firm texture is a good sign. Kale can be harvested by hand or by machine, although this machine technology is rarely affordable. Hand-harvested kale is bunched with three to five stalks, washed and then packed into bushel buckets. Kale harvested by machine is bulk loaded before being sent out for shipment. If going to a prepackaged mix, kale can be packed as a whole plant, bunched, or stripped. After being harvested, kale tends to be stored for a short period of time in a cold, moist condition of between 35 to 58 °F. Kale is a highly perishable crop with a high respiration rate and a shelf life of only 10 to 14 days. It is often topped with ice to create an ideal transit condition.
Kale is graded either No. 1 U.S. grade or U.S. commercial grade and is typically shipped in wire-bound crates and waxed fiberboard cartons. The No. 1 kale grade includes bunched kale that are well trimmed, not stunted, free of discolored or wilting leaves and free from decay or damage caused by bud burn, freezing, dirt, disease, insects or mechanical damage. The U.S. commercial grade includes kale which meets the No. 1 requirements, except when leaf edges are bronze or slightly yellowish in color.
The popularity of kale and other leafy greens has recently risen due to the health benefits and convenience of prepackaged products but has also been coupled with an increase in foodborne illnesses associated with these items. Raw and fresh-cut leafy greens, such as kale, can serve as vehicles for pathogens that cause foodborne illness, such as Salmonella, Shiga-toxin producing Escherichia coli (STEC), Cyclospora, and Listeria monocytogenes. Listeria has more recently become a pathogen of concern with raw produce because of its ability to grow under refrigerated conditions and persist in processing facilities and equipment. Human infection occurs via the fecal-oral route and contamination of kale can occur through human handling, domesticated or wild animal feces, harvesting or processing equipment, soil, or water. Contamination and cross-contamination can occur anywhere along the farm-to-fork continuum, including growing fields; cooling, storage, packaging, and processing facilities; transportation; retail establishments; and homes.
Kale is typically minimally processed and can be marketed as a raw agricultural commodity, such as raw uncut kale, or fresh-cut produce, such as pre-cut, prepackaged, or ready-to-eat mixes. As kale is generally consumed uncooked or raw, it is especially important to employ food safety risk management practices during all steps of production and processing. Appropriate and clear labeling of kale products is also vital, as consumers may be unable to differentiate between products that should be washed before consumption and ready-to-eat products that do not require washing. Human pathogens that may be present on the surface of kale may not be completely eliminated by washing, as these microorganisms adhere to produce surfaces and may be present in areas where water cannot penetrate. Microorganisms also more strongly adhere to cut produce surfaces than uncut ones. Due to the difficulty of removing microbial contamination, methods that prevent contamination are preferred over elimination methods. Consumers should store kale and other leafy greens at 35 to 40°F, wash hands before handling, use clean cutting boards and other utensils for preparing, wash products that are not ready-to-eat, and observe “use by” dates on prepackaged products or otherwise consume produce within one week of purchase. Following the preventative measures included in Good Agricultural Practices (GAPs), Good Manufacturing Practices (GMPs), Good Handling Practices (GHPs), and Sanitation Standard Operating Procedures (SSOPs) during production, postharvest handling, and processing are crucial for preventing microbial contamination of kale and other leafy greens. Education and training of growers and handlers throughout the farm-to-fork continuum is also important.
The Produce Safety rule went into effect on January 26, 2016 as part of the U.S. FDA Food Safety Modernization Act (FSMA) and establishes science-based minimum standards for the safe growing, harvesting, packing, and holding of fruits and vegetables intended for human consumption. The U.S. FDA has also developed the “Draft Guidance for Industry: Guide to Minimize Microbial Food Safety Hazards of Leafy Greens” that contains recommended best practices to minimize microbial food safety hazards of products throughout the leafy greens supply chain. In response to the 2006 outbreak of E. coli associated with California-grown spinach, the California leafy greens industry also developed a new food safety program known as the California Leafy Greens Products Handler Marketing Agreement, or Leafy Greens Marketing Agreement (LGMA). This voluntary agreement went into effect in 2007 and is the first commodity-specific food safety program to address microbial contamination in the produce industry. To participate, firms must implement minimum standard field-level food safety practices that are audited by a third-party. Kale is included under the LGMA, as is arugula, baby leaf lettuce, spring mix, butter lettuce, cabbage, chard, endive, escarole, green leaf lettuce, iceberg lettuce, red leaf lettuce, romaine lettuce, and spinach.
Kale has made major headway since its early days as a garnish for salad bars. It is now being incorporated into its own prepackaged mixes. The consumer demand for kale has caused prices to increase by twenty cents per pound. It has been labeled a superfood and is now marketed as kale chips, salad, and is used in smoothies. It can also be enjoyed by removing the leaves from the stem and cooking them down like spinach or collard greens. Together, kale and cabbage are consumed at a rate of 7.1 pounds per person as of 2014. Kale is the 10th most consumed fresh product in the United States. Kale is sold throughout the year; however, production peaks between November and May, which is the best time to purchase the crop. The top three markets for kale are Atlanta, Boston, and Los Angeles. The high demand for kale has resulted in farmers producing 60% more crop in 2012 than they did in 2007. The perceived benefits and versatility of the leafy green makes kale an important commodity in the market.
The benefits of eating leafy greens are numerous and kale is no exception. Kale, like the majority of leafy greens, is filled with nutrients, making it worthy of its reputation as a superfood. Kale is a good source of vitamins A, C, and K and contains iron, calcium, and phytonutrients, which are known for their anti-cancer properties. The nutrients in kale each provide excellent health benefits: vitamin A supports good vision and cell growth, vitamin C promotes a healthy immune system, vitamin K aids in healing, iron is important for the red blood cells, calcium is good for bone health, and phytonutrients are good for protection against cell damage. Kale also contains omega-3 fatty acids which are known to help reduce inflammation. Kale is nutritionally jam-packed, making it an essential part of a healthy diet.
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