Dry processing environments are areas where food materials are concentrated and turned into dry particulates, or where existing dry or dried foods are processed further. It could be when a concentrated dairy formulation is spray dried and converted into a powdered infant formula or when mixing various dried spices to produce a ready-to-use spice mix. In general terms, it is the handling of low moisture foods or dry foods, such as animal feeds, cereals, dried meats, grains or seeds. These foods usually have a water activity (aw) of 0.85 or lower, which is an indication of the water that is available.
Even though microorganisms do not typically grow and multiply in the absence of moisture, they are able to survive and persist until water becomes available. Dry foods are considered a reservoir for foodborne pathogens, such as Bacillus cereus in rice cereal, Clostridium botulinum associated with milk powder, or C. perfringens in spices, amongst others. The aw necessary to prevent the growth of microorganisms is about 0.60 or less. However, food spoilage fungi and yeast can grow at a low aw of 0.60 to 0.70 even though mycotoxin production cannot occur lower than 0.80. Therefore, contaminated dry foods can enter a processing environment when robust monitoring procedures are not in place.
Other means of introducing microorganisms into the processing environment is through the air circulation system, with rodents, or through the clothing and shoes of personnel. Therefore, it is important to keep the dry processing environment dry, since the introduction of moisture could stimulate the growth of microorganisms. Consequently, the most trusted means of cleaning and disinfecting dry processing environments are ‘dry’ methods.
‘Dry’ cleaning will not give a completely clean surface but it has been demonstrated to be a strategy that prevents food safety hazards in these environments. ‘Dry’ cleaning can be performed by using brushes or scrapers, by wiping, using vacuum cleaner fittings and extraction tools, using dry ice cleaning or slightly blowing with pressurized air. Products such as cereals or grains, could also be drained naturally using gravity or can be removed using pigging. It is also important to disinfect the cleaning tools by using a disinfectant solution or using hot water, ovens or steam (> 80°C for bacteria and up to 120°C for spores). These tools should be dried thoroughly before being returned to the dry processing environment. However, ‘dry’ cleaning can only be used for non-hygroscopic and/or non-sticky products.
Since microorganisms can be introduced into the processing environment through various means, it also becomes important to regularly disinfect the food contact areas. ‘Dry’ disinfection is the method of choice, because ‘wet’ disinfection causes a loss in productivity as production can only commence once the surface has completely dried. ‘Dry’ disinfection can be achieved by wiping and/or spraying of alcohol-based disinfectants such as an isopropyl alcohol-quats mixture, applying dry heat or making use of gaseous antimicrobial agents, such as ethylene oxide, hydrogen peroxide vapour, ozone or chlorine dioxide. In some cases ‘wet’ disinfection will be necessary, but it should be seen as the very last resort or performed infrequently to prevent the introduction of moisture into the environment.
The take home message is that ‘dry needs to stay dry’. Dry cleaning and dry disinfection could reduce production downtime, while increasing water savings. If cleaning and disinfection is properly managed in dry processing environments, food safety risks can be low.
- Moerman, F. and Mager, K. (2016) Chapter 35 - Cleaning and Disinfection in Dry Food Processing Facilities, Editor(s): Huub Lelieveld, John Holah, Domagoj Gabrić, In Woodhead Publishing Series in Food Science, Technology and Nutrition, Handbook of Hygiene Control in the Food Industry (Second Edition), Woodhead Publishing, 2016, Pages 521-554, ISBN 9780081001554, https://doi.org/10.1016/B978-0-08-100155-4.00035-2.
- Beuchat, L., Komitopoulou, E., Betts, R., Beckers, H., Bourdichon, F., Joosten, H., Fanning, S., and ter Kuile, B. (2011). Persistence and survival of pathogens in dry foods and dry food processing environments. Report of an International Life Science Institute (ILSI) expert group. http://www.ilsi.org/Europe/Documents/Persistence%20and%20survival%20report.pdf