Developing an air impingement dry cleaning device and investigating the factors affecting nonfat dry milk residue removal from stainless steel surfaces

Dry cleaning has been identified as one method for controlling allergen cross-contact or pathogen cross-contamination in low-moisture food (LMF) environments without introducing moisture. Therefore, an air impingement cleaning device was custom-designed and explored as a dry cleaning method to remove nonfat dry milk (NFDM) residue on stainless steel (SS) surfaces. We investigated the effects of water activity (a_w) of NFDM, residue thickness (THK), nozzle diameter (ND), ratio of nozzle height (NH) from the SS surface to the ND (NH/ND), and air pressure (AP) on the NFDM residue removal. During dry cleaning, the maximum wall shear stress (WSS) induced by airflow on SS surfaces was measured using the oil film interferometry method. The experimental results showed significant effects of all investigated factors on the removal time of NFDM residue and maximum WSS. The time to remove NFDM residue from SS surfaces increased with the increases of a_w, ND, and NH/ND, and decreased with increasing AP. The maximum WSS decreased with the increases of ND and NH/ND and increased with increasing AP. The developed air impingement device and obtained experimental results could help facilitate the practical application of dry cleaning technology to prevent cross-contact and cross-contamination in dry food manufacturing environments and improve LMF safety.