Jun 21, 2018

Food safety tactics key for hydroponic production

The number of small-scale, hydroponic producers is growing fast because of the demand for locally-grown food, but with 48 million cases of foodborne illness in the United States every year, even small producers must ensure their produce is safe.

“We all have a responsibility to ensure safe produce,” said Beth Scheckelhoff, Extension educator at Ohio State University based in Putnam County, Ohio. “The safety of your produce affects your relationship with your customers. It affects your bottom line. What if you are identified as the grower in a food illness outbreak?”

Scheckelhoff was a speaker at a recent hydroponic greenhouse workshop at the Ohio Agricultural and Research Development Center at Wooster, Ohio.

There are challenges with fresh produce. It’s frequently consumed raw. Bacteria can multiply quickly. Small doses of contaminant can make people sick.

“Once a contaminant is introduced, it is very difficult to remove it,” Scheckelhoff said. “As producers, we are trying to be proactive and not allow contamination in the first place.”

The USDA Good Agricultural Practices (GAP) program was initiated to address on-farm food safety hazards associated with fresh fruits and vegetables. The program is voluntary and market-driven. “A wholesaler may require you to be GAP-certified,” Scheckelhoff said.

The FDA’s Food Safety Modernization Act’s (FSMA) Produce Safety Rule requires growers to assess, correct and document the produce safety risks in their operations.

“Draw a map of your property,” Scheckelhoff said. “What is around you? What risks can you identify by mapping out your farm?” In rural areas, contamination risks could come from livestock on the farm or deer in nearby woods. In urban areas, risks could come from parking lot runoff or dumpsters behind nearby stores.

Contaminated water, be it used for irrigation, hand washing or postharvest handling, is a leading source of produce contamination.

“Different water sources have different risks,” Scheckelhoff said. Surface water has the greatest contamination risk because it’s exposed to the environment. “If you’re drawing from a river, there’s always the question of what’s been put in the water upstream,” Scheckelhoff said.

“Groundwater has less contamination risk than surface water. Municipal water sources are generally considered to have the least risk because they must have no contamination from E. coli.”

Generic E. coli is an indicator microorganism for evaluating water contamination. Tests for water quality must include an actual number of generic E. coli CFUs (colony forming units). Other types of tests don’t confirm the water is uncontaminated.

Postharvest water used for washing cleaning or packing equipment or other food contact areas must be potable water and have no detectable E. coli. “If you’re cooling with ice, the ice has to be made with potable water,” Scheckelhoff said. “When possible, we advise growers not to wash their produce. Washing has the potential to introduce another source of pathogens.”

If you must wash produce, use potable water, add a sanitizer and keep the water temperature 10˚ F warmer than the produce pulp. “Putting warm tomatoes into cool water can internalize contaminated water into fruit,” Scheckelhoff said. Give stem scars time to heal, too, before washing.

Use single use paper towels if drying fruit. Using rags or towels could spread contamination.

Food contact surfaces must be properly cleaned and sanitized. Cleaning is the act of washing a surface to remove foreign material. Sanitizing is the process of applying a disinfectant to the already cleaned surface. The sanitizer must be labeled for food-grade use.

“Cleaning is physically removing any dirt or debris,” Scheckelhoff said. “Sanitizing is a second step. You can’t sanitize a dirty surface.”

Reusing harvest containers is an issue. Wooden or cardboard containers cannot be cleaned thoroughly enough to reuse without risking contaminating the produce. Disposable, plastic liners in the containers is a good option.

The contamination risk of soil amendments depends on the type of material. Properly composted animal manure and plant material poses the least risk.

Composted teas pose a greater risk. Improperly composted manure poses a greater risk and raw animal manure the greater risk.

Both domestic animals and wildlife can carry human pathogens. Tracks, feces or damaged produce can all indicate wildlife intrusion into your produce fields. “Create a no-harvest zone around fecal contamination and tell your employees,” Scheckelhoff said. There is no size requirement for the no-harvest zone, but some recommendations call for a radius of five feet around the point of contamination. Document the intrusion and corrective action.

Noise makers, netting and decoys may deter animal intrusion, but vary the methods so the animals don’t get used to them.

Domestic animals are also a concern. Having cats in a facility for rodent control is a common practice, but that could introduce contaminates. “We must eliminate all animals from the produce area,” Scheckelhoff said.

Keep poison-baited, rodent traps outside of the building and only use live traps within a building. Baited traps generally have some kind of poison in them and can be a source of contamination.

“Workers are your best line of defense,” Scheckelhoff said. “Properly train your workers.”

All workers should wear clean clothes, maintain personal cleanliness, wash frequently and properly, and only eat, drink or use tobacco products in designated areas. “What are your policies? Do you have policies?” Scheckelhoff asked. “Every greenhouse should have a health and safety plan.”

Proper hand washing is the most important message to give workers. “Hand washing is your first line of defense,” Scheckelhoff said. “We don’t know what organisms are in the dirt, but we can wash our hands.”

Hand sanitizers are not a substitute for washing your hands with soap and water. Sanitizers are not effective when applied to visibly dirty hands. You can build your own hand-washing station as long as you have potable water, a catch basin, soap and single use paper towels.

Recognize the signs of workers being sick and send them home if seriously ill. Workers with minor illnesses may be able to do jobs that don’t involve handling produce or puts them in direct contact with other workers. Keep records of worker illnesses and injuries.

“Do workers know what to do when they’re sick?” Scheckelhoff asked.

Store produce that’s going to market in clean and sanitized containers. “Make sure your containers are off the ground,” Scheckelhoff said. “If you clean them, don’t put them back on the ground.”

Do not use vehicles to haul produce that have hauled animals or chemicals. Inspect all vehicles before loading and cover them after loading. “If you have a vehicle dedicated to transporting produce, that’s ideal,” Scheckelhoff said.

Consider developing a farm food safety plan that includes all of your farm policies and standard operating procedures. The plan should be able to tell everyone how to prevent or reduce food safety risks and should say what to do, who should do it, how to do it and what to do if something goes wrong.

– Dean Peterson, VGN Correspondent

Beth Scheckelhoff, Extension educator at Ohio State University, outlines food safety practices for hydroponic produce growers. Photo: Dean Peterson