Mould contamination in production of semi-hard cheese

Air, equipment, plastic film, brine and milk were sampled from four cheese factories in Norway during the period September 1997 to May 1999 in order to identify the critical points for mould contamination in the production process. Altogether, 672 samples were collected. Penicillium brevicompactum was the most frequently isolated species from three of the factories, while Geotrichum candidum was the most frequently isolated species from the fourth. P. commune, P. palitans, P. solitum and P. roqueforti ss. roqueforti, all common contaminants on cheese, were found in samples of air and equipment, and the former was also isolated from plastic film. The results in the present study showed that the mould levels in the cheese factories varied between the different control points. The mould levels at some of the air control points had high mould counts while the mould levels in milk and brine, on equipment and on plastic film, generally were low. The fungi at the control points with high mould levels consisted of common cheese contaminants as well as species not commonly isolated from cheese. The statistical analysis showed that air was the major source of the important cheese contaminants P. commune and P. palitans during the production process. High quality air with low number of cheese contaminants in production rooms, especially the wrapping room, is important in order to reduce mould contamination.