by Sally Colby
Both consumers and regulations demand that fruit and vegetable production maintain a certain level of cleanliness, which begins with keeping the packing house and the equipment in it clean and sanitary.
Chris Callahan, Extension associate professor of ag engineering at the University of Vermont, focuses on the application of engineering practice to food systems. He said hygienic design is the basis for keeping food processing equipment clean and sanitized.
“Hygienic design is about intentionally creating more spaces or equipment so they can actually be cleaned and sanitized,” said Callahan. “At the root of the practice is the fact that microorganisms are super small, and pretty persistent. They can live in tiny spaces if we give them the right conditions.”
Callahan explained that hygienic design integrates design features and practices into equipment and buildings to minimize or eliminate “harborage” – places where water and pathogens can enter and are protected from cleaning, sanitizing and drying. Harborage can lead to cross-contamination between processing batches as well as premature corrosion and rot of equipment materials.
The first principle of hygienic design is maintaining visible and reachable surfaces. “If you can’t see it and can’t reach it, how are you going to clean or sanitize it?” said Callahan. “We have to be able to get at and reach what we’re trying to clean, and have to be able to see it to know we’ve done the job well.”
One piece of equipment that can be difficult to clean is a brush washer. The brushes can prevent the operator from determining whether every part of the equipment is clean. A rinse conveyer is more wide open and uses water pressure instead of brushes. However, water under pressure results in spray, so it’s important to examine all interior surfaces for food debris.
An important key design feature in equipment is an access panel that makes use of “tool-lessness” – when things can remain in place and be taken apart more easily if there are fasteners that don’t require a tool. Examples include threaded knobs or wingnuts instead of a half-inch bolt that requires a wrench. The goal is to make disassembly easier for routine maintenance or cleaning.
Callahan suggested establishing a good lockout/tagout system that ensures power is completely disconnected. The goal is no power – no batteries, capacitors or motors can possibly run while someone is working on the machine. Water should also be disconnected when working on machinery in favor of a secondary water source for cleaning.
All surfaces should be smooth and cleanable to enable efficient and complete cleaning as well as sanitizing and complete drying. Porous surfaces such as plywood are potential harborage areas that cannot be cleaned or dried completely. Brushes used to scrub outer surfaces of produce work well for that job, but tend to collect plant matter and can be difficult to clean.
Barrel washers, especially those constructed of wood staves, can be challenging to sanitize and dry. The gaps between the wood staves and round hoops tend to accumulate dirt and food debris. When water is introduced, it becomes a transmitter of anything that’s on one part of a machine and moves it to another part.
Callahan said barrel washers are often converted to stainless steel. However, the smooth stainless steel makes it difficult to tumble vegetables properly, so the grower sometimes adds carpet and wood planks to provide friction while tumbling the produce. The challenge becomes how to clean carpet in a way that you’d want to eat from it. Instead of carpet and wood, Callahan suggested using removable stainless steel L-channels or brackets to turn the product. “We need to be able to tumble the product,” he said, “but we also need to be able to get things out of the machine.”
The addition of carpet to an apple sorting table softens the impact of fruit on metal but can be difficult to clean. Callahan suggested using pool noodles that can be removed for thorough cleaning and sanitization. “The key point is to make sure surfaces on equipment are smooth and cleanable,” he said.
Avoiding collection or harborage points involves eliminating any areas where water or organic matter (soil, plant matter) may collect that can lead to pathogen growth. Look for niches, lap joints and sandwich joints that need extra scrutiny. Flat or concave horizontal surfaces should also be avoided. Callahan said intermittent welds in steel material can lead to harborage while a continuous weld that’s been ground smoothly helps deter accumulation of organic material.
A rotary sorting table is often placed at the end of a brush conveyer line to allow workers around the table to sort crops by size. Such tables come with adhesive foam, which Callahan said is often retrofitted with other material to suit the farm’s needs. The result is harborage points and material that’s difficult to clean. Callahan suggested using material that’s attached during use but removable for cleaning.
Floors are worth attention due to harborage potential. Coving and curving of floors and walls can eliminate sharp corners created where they meet. “This helps water intrusion into the frame wall,” said Callahan. “If you incorporate coving, the rounded transition between the vertical curve and the floor, it helps make sure you can thoroughly clean the joint where the two come together.”
Callahan often sees potential for harborage on sinks and tables where the edges may not be open. “Sometimes the edges curl back on themselves and leave a bit of a crimp underneath,” he said, “which makes it difficult to get them completely clean. If you can’t see it and can’t reach it, you probably aren’t going to clean it.”
Materials should be compatible with both the product being handled and the cleaning and sanitizing processes. Compatibility considerations include water, cleaners, detergents, sanitizers and cleaning tools. Stainless steel, coated materials, plastics and concrete are typically compatible materials. Callahan urged producers to look beyond food contact surfaces and consider areas with rubber seals, bearings and electrical housings.
Preventing contamination covers a broad range of potential issues, including issues around equipment and buildings. “Think about handling systems and buildings in such a way that we protect the product from contamination,” said Callahan. “This could include birds, rodents, pets, chipping paint or chemicals stored in the same place as the produce washing area.” Consider the path water takes after it’s used and determine how to prevent backflow. A narrow trench drain with a removable grate will help water drain properly.
“One way to avoid cross-contamination is to make sure things are always flowing in the direction we want them to,” said Callahan. “Make sure we’re avoiding interruptions, delays and bottlenecks, and planning for movement. It means thinking through how product comes in from the field, goes through a wash cycle, into a cooler and packed out. Ideally, this would be a straight, single-pass flow. Drains take wash water away; culls and seconds are taken out and go on a pathway away from the wash area. We’re always working to make sure things are moving from the field to the consumer, and also in the direction from most dirty to most clean. Make sure, as always, we’re separating product from waste, including drain water.”
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