Analysis of Air Impingement for Removal of Nonfat Dry Milk Deposits from Stainless Steel Surface

Veeramani Karuppuchamy
Graduate (PhD)
Dr. Dennis R. Heldman
Food Science and Technology

Cleaning and sanitization are critical components of manufacturing operations for dry food products and have direct impact on control of cross-contamination involving microbial pathogen populations. Recent foodborne outbreaks and recalls associated with low-moisture foods emphasize the importance of these control measures. Although water is most often used for cleaning and sanitization, the potential for completing these processes during dry methods deserve serious consideration. The overall objective of this study was to evaluate effectiveness of air impingement technique as a cleaning method without water.
Nonfat dry milk (NFDM) was used as model food system for evaluation of the effectiveness of air impingement for removal of dry food deposit. A 0.4 mm layer of NFDM was uniformly applied on stainless steel (SS) coupon with 32 micro inch surface finish. The samples were equilibrated to water activities of 0.33, 0.44, 0.576, and 0.76. Then, the samples were conditioned by holding for 1 to 7 days after reaching equilibrium at a given water activity (also referred as conditioning time). Air impingement with maximum wall shear stress of 4.17 to 9.48 Pa was used to remove NFDM deposits at a distance of 32 mm from nozzle. The rate of removal from the coupon surfaces was measured and a relationship between the rate of removal and wall shear stress was established for deposits at each water activity.  

The NFDM deposits with water activity of 0.33 was removed most effectively. As the water activity of deposits increased, the rate of removal reduced. In addition, the rate of removal decreased as the conditioning time increased. Finally, the relationships describing the increase in rate of removal with increased maximum wall shear stress have been established for each water activity and conditioning time. The removal efficiency varied from 6% to 100% based on the change in mass removal from the surfaces. 

The application of air impingement provides a method for removal of low and intermediate moisture foods from surfaces within manufacturing operations. This approach provides a viable alternative to the use of cleaning and sanitization with liquids. Further studies are needed to validate the effectiveness of removal with air impingement.