The growth and survival of the psychrotroph Penicillium spinulosum in paperboard was studied along with the wicking characteristics of ultra-pasteurized milk to understand sporadic fungal contamination of ultra-pasteurized, extended shelf life milk products. Previous research has indicated paperboard packaging as a potential source for the fungal contamination. Migration from paperboard to ultra-pasteurized skim milk during a 60-day shelf life, was investigated by inoculating condia (spores) into sterilized paperboard squares (57.2 by 57.2 mm) made from ultra-pasteurized milk cartons. Test-squares were sealed on three sides and inoculated at 3.2, 6.4, 9.5 and 12.7 mm from the uncoated (unskived) edge. The surrounding milk was tested for the presence of the fungus. Penicillium spinulosum was detected in 84% of samples at 3.2, 72% at 6.4, 50% at 9.5, and 28% at 12.7 mm from the uncoated edge. Survival in paperboard was investigated in sealed paperboard test-squares incubated in ultra-pasteurized skim milk at 7°C every 10 days up to 60 days. Penicillium spinulosum survived in the interior of paperboard for the entire incubation period. Survival was also measured on all test-squares for which P. spinulosum was not detected in the surrounding milk in the migration study. Penicillium spinulosum was detected in 94.4% of all negative samples. The wicking characteristics of ultra-pasteurized skim and whole milk were measured in four boards from gable-top cartons for ultra-pasteurized milk products. Test-squares were sealed on 3 sides and incubated in ultra-pasteurized skim or whole milk at 7°C. Wicking distances were measured every 10 days up to 60 days. A significant interaction was seen between the types of paperboard and milk. It is most likely that P. spinulosum at all inoculation distances had access to milk as a source of nutrition by day 40 in the migration study. / Master of Science