Editors’ note: This is part 1 of a two-part series on dry cleaning. Part 1 looks at the rationale for dry cleaning, and the challenges that can accompany the process. Part 2, which will publish in the October/November 2021 issue of Food Quality & Safety, will focus on solutions to these challenges.
We tend to think of dry cleaning in the food industry as being related only to those food plants that undertake dry/low water activity (aw) food and ingredient processing. But, dry cleaning and sanitization can be a valuable option in the control of microbial hazards for any processing plant. In this series of articles, we look at the rationale, challenges, and solutions related to microbial control through controlled use of water, dry cleaning, and other sanitization techniques.
The production of dehydrated foods and food ingredients with low aw, such as cereals, chocolate, cocoa powder, dried fruits and vegetables, dried meats, egg powder, herbs, spices, condiments, milk powder, whey protein powders, pasta, powdered infant formula (PIF), grains, and seeds is popular, due to their long shelf life and less stringent holding and storage condition requirements.
Low-moisture and low aw foods also have advantages in that they are less prone to spoilage. Although low aw foods seem to have clear advantages with respect to controlling the growth of microorganisms, there are, nevertheless, major concerns regarding the survival of pathogenic microorganisms, and outbreaks linked to low aw foods and dry ingredients have been reported. Major foodborne pathogens of concern include Salmonella spp., Bacillus cereus, Cronobacter sakazakii, Clostridium spp., E. coli O157:H7, and Staphylococcus aureus.
Many food processors and consumers mistakenly believe that dried foods are sterile or that microorganisms do not survive in dried food due to their low moisture content. However, many microorganisms, including pathogens, are able to survive drying processes and, while they may not grow, vegetative cells and spores may remain viable for several months or even years. Microorganisms are known to persist longer in dried foods and dry food processing environments than in foods and environments with higher moisture content and low aw. It’s also important to note that foodborne pathogens in low aw foods and environments may have an increased tolerance to heat and other treatments that are lethal to cells in high aw environments, making them very difficult to eliminate in many dry foods or dry food ingredients without compromising the quality of the food product.
Potential sources of microbial contamination in dried foods include incoming raw materials and ingredients, the external environment (surroundings, water, air, pests), inadequate cleaning and sanitation, inadequate processing, and post-processing contamination, mainly through the food plant environment. Primary strategies for reducing microbial pathogens include:
- Supplying specifications segregating hygiene areas to separate dry and wet processing areas;
- Controlling human and material movement in the plant to avoid cross-contamination,
- Implementing effective dry-cleaning and wet-cleaning practices; and
- Employing an effective environmental pathogen monitoring program, particularly in a facility producing ready-to-eat (RTE) foods.
The Food Safety Modernization Act (FSMA), signed into law in January 2011, represents a paradigm shift from reaction-based systems to prevention-based systems and clearly places the burden of assuring food safety on the food manufacturer. The “Current Good Manufacturing Practice Hazard Analysis and Risk-Based Preventive Controls for Human Food,” or the Preventive Controls for Human Food (PCHF) rule, requires food processors to identify “known or foreseeable” hazards in foods, using a risk-based hazard analysis, and identify preventive control(s) to mitigate the hazard identified. In addition, management components such as monitoring; procedures for corrective action, verification, and record keeping; supply chain programs; and recall plans are also required. The FSMA PCHF is based on the modified cGMPs and includes sanitation controls. The PCHF regulation emphasizes environmental monitoring programs, as well as targeted sampling and testing, as appropriate ways to control microbial hazards in RTE foods.
Other FSMA regulations, including Foreign Supplier Verification Programs for Importers of Food for Humans and Animals (FSVP) and the Sanitary Food Transportation Act (SFTA) may also apply to dry food manufacturers.
Controlling the potential for dry/low aw food contamination with foodborne pathogens should therefore focus on preventing this problem through implementation of efficient cleaning and sanitation procedures in the food processing environment. Food processing environments in which dried foods are handled must be maintained at low humidity and kept dry, a requirement that gives rise to the need for specific cleaning and sanitizing procedures. The challenges of cleaning and sanitation in dry food plants and specific approaches to accomplishing efficient and effective sanitation and hygiene are discussed below.
Dry cleaning is hard work. Let’s face it: Cleaning with water is easy, fast, and effective. There also seems to be something in our psyche that makes us enjoy using water. By contrast, dry cleaning is hard work, tedious, and awkward. It often takes considerably longer to do than cleaning with water and adds pressure on an already beleaguered hygiene team to minimize cleaning windows in favor of production.
So, why should we dry clean? Well unfortunately, for all of its benefits, water also comes with some serious downsides, especially when it comes to its use in the food industry.
Water promotes microbial growth and spread. We know that some microbes can survive in dry environments, but most require five things to grow: nutrients, water, the right temperature, the right atmosphere, and time. Once established, microbes can spread throughout an environment via vectors, namely on surfaces (hands, equipment, packaging), through the air (particles), and via water (droplets, aerosols, splashes, standing water). The presence of water significantly increases the risk of both microbial growth and spread.
In a food factory, access to nutrients will rarely be a problem. Similarly, working temperatures and atmospheres must be kept at levels people can tolerate—levels that tend to also favor most microbes. Consequently, within a dry/low aw food factory, there are generally only two things we can control—time and water. We deal with time through the use of cleaning windows that remove contamination at a frequency that limits microbial growth. But how do we clean without water?
Water spreads contamination. We know from various studies that water, in the form of droplets, aerosols, and standing water, can significantly aid the spread of contamination. Research conducted at Campden BRI demonstrated that “contamination” on a wet boot can be transferred over 24 m on a dry floor. However, if that floor is wet, the transfer distance increases to more than 35 m. If the boot is contaminated with microbes, a few can be detected on a dry floor for up to four steps, but they can be found for more than 15 steps on a wet floor.
Unfortunately, some of the measures we take to reduce the spread of contamination may actually increase it. Take handwashing, for example, which forms a fundamental part of any food production site’s personal hygiene policy. This action is aimed at the removal of contamination from peoples’ hands and, consequently, minimizing the risk of contamination transfer to the food product. However, the act of handwashing itself can lead to the spread of contamination.
Studies conducted by Campden BRI have demonstrated that a significant number of water droplets (circled in pen in Figure 1), many of them carrying microbial contamination (as indicated by the number of colony-forming units developed on agar plates arranged on the floor around the handwash sink in Figure 2), fall onto the surrounding floor during handwashing. Imagine the amount of water and contamination that could accumulate in this area at the start of a shift and, subsequently, be transferred by footwear into the production area.
It’s not just the floor that can become contaminated during handwashing. Campden BRI studies have shown that the protective clothing worn by food production area workers can also be affected.
Additionally, if a worker’s hands are dried using high velocity air, the risk of cross-contamination from water droplets to both the floor and the protective clothing worn can be increased and, if they are not dried thoroughly after washing, any microbes remaining on the hands are more easily transferred to any surface subsequently touched.
Even in a wet-cleaned food production area, the use of some wet-cleaning activities can significantly increase the risk of contamination spread. The model in Figure 3 illustrates the spread of water droplets generated when a high-pressure hose is used to clean a slot drain. In this case, the droplets spread a minimum distance of 7 m and at a height of up to 3.5 m, meaning that they could potentially settle on food contact surfaces.
Consequently, the way we use water for cleaning, even in wet food production environments, needs to be considered carefully.
In part 2 of this article, we’ll look at the solutions to these challenges, including ways in which we can reduce the risk of microbial growth and spread through use of modified personnel hygiene and entry systems. We’ll also cover dry cleaning and sanitization techniques.
Smith is global hygiene specialist at Vikan Ltd. Reach her at [email protected]. Dr. Vasavada is professor emeritus of food science at the University of Wisconsin-River Falls and co-industry editor of Food Quality & Safety. Reach him at [email protected].