Outbreaks have occurred in the past from consuming food products made with raw milk. One of the potential pathogens in raw milk, "Listeria monocytogenes", can survive the pasteurization process and contaminate post-pasteurization environments. Milk and dairy products made with that milk then become recontaminated. Consistent contamination persists by bacteria survival in bio-films within the processing systems. One food item that has commonly used raw milk in its production in the past is cheese. Several different types of cheeses made with raw milk are consumed by a large portion of the United States population, including soft cheeses. Since Gouda cheese has a 60-day aging period prior to its consumption, it has previously been hypothesized that no bacteria would persist through that time. A review study published in the "Journal of Food Protection" showed that "E. coli" 0157:H7 has the ability to persist through the aging period of Gouda cheese. The study's evidence included three different outbreaks prior to 2013 associated with this specific strain of "E. coli" in Gouda cheese.