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Cheese Safety 101

Part 1: Don't fall off the ladder

Dr. Art Hill
Department of Food Science
University of Guelph,
Guelph, ON, N1G 2W1

Raw milk cheese was a major theme at the Annual Meeting of the Ontario Cheese Society in March 2006. Following that meeting it was agreed that a series of articles on cheese safety management in the OCS news letter would be helpful. It is my privilege to be the principal author of the series, but I will enlist the advice and help of colleagues. This first article sets the direction and tone of the series and introduces the concept of risk.

At the outset, let us be clear that this series is not about raw milk cheese; it's about cheese safety. Pasteurization is only one strategy of several equally important safety management tools that are available to the cheese maker. For example, a well known 1998 cross-Canada outbreak of salmonellosis was associated with Cheddar cheese in Schneider's Lunch Mates, a snack that was mainly consumed by children. Although the source of the infectious doses of Salmonella enteritidis in the cheese was never identified (Laura Eggertson, Toronto Star, April 3, 2023), it was evidently due to post-pasteurization contamination of the cheese milk or the cheese. In other words, proper pasteurization apparently occurred, but was not sufficient to prevent the outbreak.

It is my hope that Cheese Safety 101 will help cheesemakers understand and apply safety management tools to ensure production of safe cheese, regardless of whether the cheese is made from raw or pasteurized milk. Our focus will be on technological principles, which will help build a foundation for application of GMP (Good Manufacturing Practice) and HACCP (Hazard Analysis and Critical Control Points), but we will not discuss GMP and HACCP in particular.

Those technological principles or biochemical and physical 'tools', as I like to describe them, include temperature history, acidity (pH history), water activity, salt and certain additives. We'll get to those tools and how to apply them in subsequent news letters. Here, in Part 1 of Cheese Safety 101, we begin with a description of risk. Risk is the other side of the Food Safety coin ­ safer food is achieved by reducing the risk associated with contamination and growth of pathogenic microorganisms.

Eating, relative to other activities, such as riding in a car, is a low risk activity, at least with respect to acute injury and morbidity. Some nutritionists may argue that poor food choices (of course, with tongue-in-cheek I would say that cheese is never a poor choice), over the long term, constitute a high risk of injury and morbidity. However, our discussions in this series will focus on microbial safety, which in most cases is a short term risk. There are also chemical hazards associated with cheese (e.g., antibiotic residues), but these are quantitatively small relative to microbial hazards.

To say that eating is a low risk activity, is to correctly imply that there is some risk associated with eating. So, it becomes important to manage risk, and to manage it, we need to identify and quantify it. Risk can be described in quantitative terms as expressed in the following equation, where severity is an estimate of the potential negative consequences of a food incident, and probability is the probability that the incident will occur.

Risk = (severity of the event) x (probability of the event)

For example, consider the event of a painter falling off a ladder, which we will designate, Event A. The probability of Event A increases if the ladder is rickety. The severity of Event A increases with the height of the painter on the ladder. Severity also increases if the ladder is positioned over a shark tank! Some factors that determine the severity and probability of microbial food borne illness incidents are listed in Table 1.

The goal of risk management is to reduce the risk associated with a particular event to as close to zero as possible by reducing its severity or probability or both. In practice, the cheese maker should do both. That is, preventive measures should be taken to reduce the probability of cheese contamination with pathogenic organisms and to minimize their growth if contamination should occur. At the same time, recognizing that there is always some risk of contamination and growth, traceability and recall protocols should be in place to reduce the severity (limit the extent) of an outbreak should it occur.

Our discussions in this series will focus on the second term in the risk equation, namely, reduction of the incidence and growth of pathogenic organisms in cheese. As it turns out, the properties of milk and traditional cheese making procedures provide many 'built in' factors that the cheese maker can employ to enhance cheese safety articles.

Those parameters will be described in subsequent Cheese Safety 101 articles.

Next: I have seen the enemy and he speaks Latin. All you need to know about pathogenic organisms.