Food Source Information Collard Greens

Collard greens are a popular leafy green used today in various cuisines across the globe. They are a broad-leafed, easy-to-grow biennial and are an Acephala (meaning without a head) variety of the Brassica family. The name “collard” originates from the Anglo Saxon term “colewort,” meaning wild cabbage or cabbage plant. The cultivated collard greens of today are related to wild, primitive cabbages dating back over 2000 years to the Mediterranean and the Asia Minor regions. Collards made their way to the Americas through various trade routes and have since become a staple food product in the southern United States where they are commonly associated with regional culture. The cooking methods used for many collard dishes are connected to African customs dating back to the time of slavery in the U.S. Traditionally, collards were served with leftover foods, like ham hocks, and eaten with the cooked-down juices, also known as “potlikker.” Collard green recipes have been passed down through generations of southerners, along with the superstitious belief that eating collard greens on New Year’s Day will ensure financial prosperity throughout the year (the green leaves represent money).

The major varieties of collard greens include Champion, Georgia Southern, Morris Heading, Vates, and Ole Timey Blue. Collards can be identified by their medium green hues and their fibrous, oval-shaped leaves. They have a mild flavor that can be enjoyed in the tough, raw form or that can be cooked down until the leaves become tender. Like other leafy greens, this cool-season crop is adaptable and nutritious, making it an important vegetable to incorporate into healthy diets.

As with all leafy greens, collard greens are 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 collard greens. Between 2000 and 2020, at least 3 collard green-associated outbreaks were reported to CDC’s National Outbreak Reporting System (NORS), causing 45 illnesses, and no hospitalizations or deaths.

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 were no known illnesses.

In 2017, CC Kitchens in Ohio recalled slaw and salad kits after environmental testing at the facility produced a positive result for potential contamination with the pathogen Listeria. The company quickly issued a recall between May 31 and June 5, and no illnesses were reported.

In 2015, Inventure Foods Inc. issued a voluntary recall of its Fresh Frozen IQF brand collard greens after Listeria was found in its Jefferson, Georgia facility. The frozen collards had been distributed to retail outlets, supermarkets, and mass-merchandise stores across 23 states. There were no known illnesses.

The southern states are primarily responsible for the bulk of production of collard greens in the United States. In fact, South Carolina chose collard greens as its state vegetable and Georgia is the second top producing state for collard greens.

There are two major types of growers of collard greens: fresh-market growers and processing-market growers. Fresh market growers may be categorized as either large-scale or small-scale, depending on the size of their operations. Most collard green production takes place on small-scale operations, but there are a few large-scale commercial operations. Processing-market greens are eventually sold as canned and frozen products. While visual attractiveness of the greens is not nearly as important to the processing market, collards produced for fresh-market sellers must be fresh and attractive in appearance.

Pre-Harvest

Collard greens thrive best in the spring or fall seasons due to the cooler conditions. Collards planted in fall are often favored because the leaves are believed to taste sweeter after the first frost. Although they do well in most types of soil, heavier soil loams help to produce higher yields in fall, and well-drained sandy soils are best in the spring season. The plant needs average temperatures of 60 °F to 65 °F, but can withstand the light freezes and frosts which accompany the cooler season. Collard greens are often direct seeded and thinned or transplanted for production. The plant takes anywhere from six to eight weeks to be ready for transplanting and generally requires 12 to 18 inches of spacing. Collard greens, like other leafy greens, have shallow roots, requiring less water than other crops. However, it is important during germination and crop maturation to continuously provide adequate moisture to aid in the plant’s growth.

Harvest

Collard plants are often cut by hand, field-packed, and cooled before being shipped to market. However, harvesting methods depend on the market and scale of the operation. The leaves of the collard plant grow from its main stalk and can be harvested once they have grown to about 10 to 12 inches long. Removing the outer leaves first allows the plant to continue to produce throughout the season.

After being harvested, trimmed, and cleaned, the leaves are bunched together, bulk loaded, and packed 12 to 24 bunches per box. Boxed greens are then topped with ice for transport to ensure temperatures of 40 ℉ or less are maintained. Approximately 2.2 pounds of ice are required for every four pounds of collards. Collard greens have a two-week shelf life if they are stored at 32 °F to 36 °F to prevent moisture loss and to ensure crisp leaves.

Post-Harvest

Collard greens are No.1 U.S. grade when they are fresh, clean, well-trimmed, and of a color specific to the variety. The greens must not have coarse stems and should be free of discoloration, decay, or damage resulting from freezing, foreign material, disease, insects, mechanical, or any other means. The tolerances for collard grades are based on the product weight of the container, which can be no more than 10% by weight of the units of any lot.

More information on kale production provided by the United States Department of Agriculture can be found at Produce Point of Origin Database.

The popularity of collard greens 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 collard greens, 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 collard greens 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.

Collard greens are typically minimally processed and can be marketed as a raw agricultural commodity, such as raw uncut, or fresh-cut produce, such as pre-cut, prepackaged, or ready-to-eat mixes. As collard greens are frequently 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 collard greens 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 collard greens 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 collard greens 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 collard greens 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.

Collard greens have been eaten for hundreds of years and have become a staple crop for the southern United States. Although collards are traditionally served cooked, it is increasingly common to see them served raw in salads and slaws. They can be purchased fresh, frozen, or canned, and are often added to soups, casseroles, stir-fry dishes, and even smoothies. They are also popular in slow-cooking recipes, as the leaves stand up better than more fragile greens like chard or arugula. The leaves can also be used for stuffed rolls and are even pureed into pesto, sauces, and dips.

Collard greens fall under the term “soul food,” with the roots of many dishes coming from African cultures. The greens are often slow-cooked, to make them tender, and then eaten with the potlikker juices. Collard greens are fibrous and tough and benefit from slow braising or steaming, which also helps produce a milder taste. They are often prepared with other similar green-leaf vegetables, such as spinach, kale, turnip greens, and mustard greens, in a cooked southern dish called “mixed greens”. Collard leaves can also be sliced thin and made into a type of fermented sauerkraut called “collard kraut” which is typically served with fried chicken, pork chops, or flat dumplings. This is the traditional style of preparation in North Carolina, where families still gather each year to prepare their collard kraut using recipes passed down for generations. The greens are salted, packed into a container, and covered with brine. The container is then covered with a kitchen towel or loose lid and the kraut is allowed to ferment, away from direct sunlight, for about one to two weeks. After it has sufficiently fermented, it is transferred to the refrigerator.

While collards have been popular in the south for years, they are consumed in northern states as well. In 2011, the Economic Research Service of the U.S. Department of Agriculture found that collard greens were cheaper than other cruciferous vegetables in regards to the average price per edible cup, making them a nutritious alternative to more expensive vegetables. They have also become popular as a “microgreen” produce item.

The best collard greens are a deep, green color with no yellow or brown on the leaves. Smaller leaves will generally be more tender. It is good practice to wash off any remaining soil under cool water and remove the stems before consumption. Collard greens are often found on the grocery store shelves next to kale.

Collard greens are a good choice for obtaining essential vitamins and minerals. They are a rich source of dietary fibers, iron, and vitamins A, B, C, and K. Vitamin K and the antioxidants found in collard greens provide anti-inflammatory properties and Vitamin C and E contain cancer fighting properties. Collards contain a good amount of fiber which, along with Vitamins K and B, support digestion and help regulate the blood supply and blood sugar levels in the body.

1. Affairs, Office of Regulatory. Recalls, Market Withdrawals, & Safety Alerts – CRF Frozen Foods Expands Voluntary Recall to Include All Frozen Vegetable and Fruit Products Due To Possible Health Risk [Internet].
2. Beach C. UPDATED: Secret outbreak investigation targeted packaged salads in April | Food Safety News [Internet]. [cited 2017 Jul 31].
3. Brandenberger, Lynn S James, Rebek, Eric D John, others. Cool Season Greens Production (Spinach, Collard, Kale, Mustard, Turnip, Leaf Lettuce). 2016 [cited 2017 Jul 31];
4. Centers for Disease Control and Prevention. Multistate Outbreak of Shiga Toxin-producing Escherichia coli O157:H7 Infections Linked to Organic Spinach and Spring Mix Blend (Final Update) | Multistate Outbreak Linked to Organic Spinach and Spring Mix Blend | E. coli | CDC [Internet]. [cited 2017 Jul 27].
5. Clemson Cooperative Extension. Collards [Internet]. Home and Garden Information Center. [cited 2017 Aug 15].
6. Cornell University. Explore Cornell – Home Gardening – Vegetable Growing Guides – Growing Guide [Internet]. [cited 2017 Jul 31].
7. Davidson, Gordon R. B Annemarie L, Ryser, Elliot T. Efficacy of Commercial Produce Sanitizers against Nontoxigenic Escherichia coli O157:H7 during Processing of Iceberg Lettuce in a Pilot-Scale Leafy Green Processing Line. Journal of Food Protection. 2013 Nov;76(11):1838–45.
8. Department of Health and Human Services. Standards for the Growing, Harvesting, Packing, and Holding of Produce for Human Consumption. Department of Health and Human Services; 2015 Nov p. 74353–74672. (Food Safety Modernization Act). Report No.: FDA–2011–N–0921.
9. Food and Drug Administration. Program Information Manual Retail Food Protection: Recommendations for the Temperature Control of Cut Leafy Greens during Storage and Display in Retail Food Establishments [Internet]. 2010.
10. Food and Drug Administration. Inventure Foods, Inc. Issues Voluntary Recall of Its Fresh Frozen Vegetables and Select Jamba “At Home” Smoothie Kits Because of Possible Health Risk [Internet]. [cited 2017 Aug 10].
11. Food and Drug Administration. Outbreaks > FDA Investigated Multistate Outbreak of Listeria in Dole Leafy Greens Products Produced in the Dole Facility in Springfield, Ohio [Internet]. [cited 2017 Jul 31].
12. Food and Drug Administration. Recalls, Market Withdrawals, & Safety Alerts > CC Kitchens Announces Recall of Limited Number of Salad and Slaw Kits Containing Leafy Greens Due to Possible Health Risk [Internet]. [cited 2017 Jul 31].
13. Food and Drug Administration. Recalls, Market Withdrawals, & Safety Alerts > Osage Gardens Inc. Recalls Osage Gardens Organic 2oz Micro Greens Because of Possible Health Risk [Internet]. [cited 2017 Aug 3].
14. Gil, Maria I. S Maria V, Suslow, Trevor J Liesbeth, Uyttendaele, Mieke A Ana. Pre- and Postharvest Preventive Measures and Intervention Strategies to Control Microbial Food Safety Hazards of Fresh Leafy Vegetables. Critical Reviews in Food Science and Nutrition. 2015 Mar 21;55(4):453–68.
15. Leonard J. Collards [Internet]. NC State Extension Publications. [cited 2017 Aug 10].
16. Mishra, Abhinav G Miao, Buchanan, Robert L. S Donald W, Pradhan, Abani K. Development of growth and survival models for Salmonella and Listeria monocytogenes during non-isothermal time-temperature profiles in leafy greens. Food Control. 2017 Jan;71:32–41.
17. Mishra, Abhinav G Miao, Buchanan, Robert L. S Donald W, Pradhan, Abani K. Prediction of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes Growth in Leafy Greens without Temperature Control. Journal of Food Protection. 2017 Jan;80(1):68–73.
18. Texas A&M AgriLife Extension. Greeks and Romans Grew Kale and Collards | Archives | Aggie Horticulture [Internet]. [cited 2017 Aug 9].
19. The George Mateljan Foundation. Collard greens [Internet]. The World’s Healthiest Foods. [cited 2017 Aug 9].
20. U.S. Department of Agriculture. Kale and Greens (Beet, Broccoli, Collard, Dandelion, Mustard, and Turnip) Shipping Point and Market Inspection Instructions| United States Department of Agriculture [Internet]. 2008.
21. U.S. Department of Agriculture. Collard Greens or Broccoli Greens Grades and Standards [Internet]. Agricultural Marketing Service. [cited 2017 Aug 10].
22. U.S. Department of Agriculture. USDA ERS – The California Leafy Greens Industry Provides an Example of an Established Food Safety System [Internet]. [cited 2017 Jul 27].
23. UGA Cooperative Extension. Commercial Production and Management of Cabbage and Leafy Greens [Internet]. [cited 2017 Jul 31].
24. UGA Cooperative Extension. Commercial Production and Management of Cabbage and Leafy Greens | UGA Cooperative Extension [Internet]. [cited 2017 Jul 31].
25. UM Extension. Vegetable Profiles: Leafy Greens | University of Maryland Extension [Internet]. [cited 2017 Jul 31].
26. University of Illinois at Chicago. Collard Greens (Brassica Oleracea) [Internet]. Heritage Garden. [cited 2017 Aug 10].
27. University of Illinois Extension. Collard Greens [Internet]. Nutrition and Cancer Survivorship Lab. A
28. University of Illinois Extension. Collards [Internet]. Vegetable Directory. [cited 2017 Aug 15].
29. Zimet, David J. H TD, Smith, J. L. Growing collard greens for the fresh and processing markets. University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS; 2000.
30. Collard Greens – Nutrition Facts and Health Guide [Internet]. Veggies Info. [cited 2017 Aug 16].
31. Collard Greens Information, Recipes and Facts [Internet]. Specialty Produce. [cited 2017 Aug 9].
32. Collard Greens State Vegetable [Internet]. State Symbols USA. [cited 2017 Aug 10].
33. History of Dark-Leafy Greens [Internet]. Cookin’ Greens. [cited 2017 Aug 9].
34. Leafy Greens [Internet]. EatFresh. [cited 2017 Jul 27].
35. Leafy Greens & Mixed Greens [Internet]. Colorado Farm To Market. [cited 2017 Jul 31].
36. The Collard and the Kale [Internet]. Harvesting History. [cited 2017 Jul 31].