Ensuring Food Safety in Microgreens Production

In 2011, food safety laws in the United States underwent significant reform. Known as the Food Safety Modernization Act (FSMA), the law's overall objective is to focus on the prevention of food safety issues. Further, the law seeks to prevent microbial contamination and reduce foodborne illness associated with fresh fruits and vegetables. Included within FSMA is the Produce Safety Rule (PSR), which includes science-based standards for growing, harvesting, packing, and holding produce for human consumption. In general, the PSR specifically covers produce that is consumed raw. Microgreens fall into that category.

Understanding Microgreens and Their Risks

Microgreens and sprouts are often confused, but they differ in growth stages, harvest methods, and associated risks. Sprouts are harvested earlier, with seeds and cotyledons still attached, and are often grown in water. These factors increase their vulnerability to bacterial contamination. Microgreens are grown until their first true leaves appear and are typically grown in soil or substrate, then harvested by cutting above the growing medium.

While microgreens have slightly lower risks than sprouts due to exposure to light, which can reduce bacteria, they share some challenges. Bacteria thrive in moist, warm environments, and these same conditions promote microgreen growth. Producers must implement stringent food safety practices to mitigate risks.

Key Areas of Risk in Microgreens Production

Worker Hygiene

Workers play a critical role in maintaining food safety. Poor hygiene can introduce pathogens to microgreens during planting, harvesting, and packaging. Worker hygiene guidelines under FSMA include mandatory handwashing and a strong emphasis on health and cleanliness.

To reduce risks:

• Train workers on proper handwashing techniques, emphasizing a minimum of 30 seconds with soap and water.
• Ensure employees wear clean clothing and footwear, especially when moving between outdoor and indoor environments.
• Prohibit sick workers from handling crops.
• Implement protocols for identifying and handling contaminated areas, such as those with bird or rodent droppings.

Water Quality

Water used in the production of microgreens is a potential source of contamination. For microgreen production, water must be free of E. coli for seed soaking, rinsing, irrigation, and post-harvest washing. If you use municipal water, you do not need to test your water, but you can request a copy of the test results to keep on file. If using a private water source such as a well or spring,  and water is found to have detectable E. coli, the grower must immediately discontinue its use. Before resuming use of the water, it must be treated with an in-line sanitizer, UV treatment, or other system that is consistently safe and adequately sanitary. Shocking the well is not a solution because it will not ensure consistent safety. Washing flats and trays is an important part of microgreen production. A standard operating procedure (SOP) should be written so that all workers know what is expected. Cleansers and sanitizers may be used. Be sure to follow the label directions when using these products.

Steps to ensure water safety include:

• Regular testing for generic E. coli, the primary indicator of contamination.
• Consider using UV light systems or approved sanitizers, such as chlorine or peroxyacetic acid, to treat water used for irrigation or washing.
• Minimize overhead irrigation, as water that directly contacts the edible portion of the crop increases risk.
• Prevent hoses and nozzles from dragging on the ground, where they can pick up contaminants.

Microgreens that are grown hydroponically often benefit from tighter water quality control, especially if pretreated with UV light or similar systems.

Cleaning and Sanitizing

Proper cleaning and sanitizing of all tools, surfaces, and equipment used in microgreens production is essential. Growers must:

• Physically clean surfaces with water and soap to remove visible dirt before applying sanitizers. Remember, "You can't sanitize dirt."
• Use food-safe sanitizers like chlorine solutions or peroxyacetic acid to eliminate microorganisms.
• Establish regular cleaning schedules for high-contact areas such as trays, clippers, and containers.
• Focus on non-food-contact surfaces, such as walls and floors
• Eliminate standing water or debris

For tools and food contact surfaces, employ a two-step process:

1. Clean - Use a soap or detergent to remove dirt, grease, and organic residues.
2. Sanitize - Apply a food-grade sanitizer to remove invisible microbial threats. Approved solutions, such as peroxyacetic acid or chlorine-based sanitizers, are commonly used by growers.

Regularly inspect and sanitize non-food-contact areas, including cooling units and equipment storage zones, to reduce pathogen buildup. If possible, expose trays and other surfaces to sunlight, which can naturally reduce bacterial loads.

Soil Media Concerns

The growing medium used for microgreens can harbor pathogens such as E. coli or Listeria. Producers should:

• Avoid potting mixes that contain biological soil amendments of animal origin, such as raw manure, which can introduce harmful bacteria.
• Source substrates like coco coir, hemp mats, or peat-based mixes from reputable suppliers. Verify they have undergone proper composting or heat treatment.
• Test soil media for generic E. coli when in doubt.
• Ensure the substrate doesn't come into direct contact with the edible parts of the microgreens during harvest.

Packaging and Handling

Always use clean containers for handling and shipping microgreens. Do not reuse any cardboard or paper packaging. Regularly inspect and clean storage areas for packaging supplies.

Compliance with FSMA and Best Practices

FSMA provides a framework for growers to improve food safety. For microgreens producers, compliance with FSMA includes:

• Regular testing of water for contamination.
• Cleaning schedules and sanitizing protocols for all harvesting and packaging tools.
• Proper training for workers on hygiene and contamination prevention.

Post-harvest washing is not recommended for microgreens unless absolutely necessary, as it can spread contamination. If washing is required, always use clean water treated to remove generic E. coli.

Proactive Risk Management

Food safety in microgreens production depends on understanding and managing the unique risks associated with this crop. By implementing effective hygiene, water quality testing, thorough cleaning, and careful selection of soil media, growers can minimize contamination risks.

Growers seeking FSMA training are encouraged to participate in upcoming webinars or reach out to local Extension offices for support. 

This work is supported by the Northeast Extension Risk Management project award no. 2023-70027-40447, from the U.S. Department of Agriculture's National Institute of Food and Agriculture.