Cheese Safety

21 Cheese Safety Management Systems

1. The Concept of Risk

In this section we explain the principles of risk analysis and draw out some applications in terms of cheese safety. This is foundational to understand and implement food safety management systems but is not intended to replace detailed training in GMP (Good Manufacturing practice or Pre-HACCP) and HACCP (Hazard Analysis and Critical Control Point). Please come back and take our online course in Cheese Safety and Quality Assurance.

Risk is the underside of the Food Safety coin; safer food is achieved by reducing the risk associated with contamination and growth of pathogenic microorganisms. So, it’s important to manage risk, and to manage it, we need to identify it and characterize it. Risk can be described in quantitative or at least semi-quantitative terms as expressed in the following equation, where severity is an estimate of the potential negative consequences of a negative 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 22.1.

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 the harm if an outbreak should occur.

This section will focus mainly on the second term in the risk equation, namely, reduction of the probability of the presence and growth of pathogenic organisms in cheese. As it turns out, the properties of milk and traditional cheese making procedures provide ‘built in’ factors that the cheese maker can employ to enhance cheese safety.

2. Risk Analysis

The WHO (World Health Organization) uses the risk analysis model as the basis for food safety assurance. Adapted definitions of the three components of the WHO model are:

  • Risk Assessment is a science based process to identify and characterize hazards, assess exposure, and characterize risk.
  • Risk Communication is interactive exchange of information and opinions about risk.
  • Risk Management is a policy based process to evaluate risk, and to select, implement, and validate mitigation strategies.

Note that there is considerable overlap and interdependence among these three components of risk analysis. That overlap appears greater or smaller depending on the specific context. For example, to assess the risk associated with Brie cheese as it is presented to the consumer, we need to consider all risk and risk mitigation factors in the entire supply chain. Among other hazards for Brie, I would be concerned about possible environmental contamination and growth of Listeria monocytogenes on the surface of the cheese during ripening and packaging. A related risk factor is that the acidity on the surface of Brie is reduced (pH increases) during ripening, creating excellent growth conditions for Listeria.  Also, there is no further treatment or process that would reduce or eliminate Listeria before the cheese reaches the consumer. So, considering the sensitivity of pregnant women and immunocompromised people to Listeriosis, I would characterize the risk as low, but would also recommend that people in higher risk groups should limit their consumption to baked Brie. That warning is one form of risk communication and in this case also a risk management strategy.

The following Sections 22.3 – 22.4 describe the principles of risk analysis (risk assessment, management and communication) in the context of cheese making.

3. Cheese Risk Assessment

Identify Hazards

We’ll review some data on sources and prevalence of cheese borne hazards in the lecture. Here we’ll identify hazards relevant to cheese making in general terms.

  • Microbial hazards occur most frequently, but chemical hazards such as antibiotics, and physical hazards such as metal contamination, must also be considered.
  • Raw milk can directly contaminate cheese with pathogenic organisms if it is not pasteurized (See Section 9.4). Pathogens from raw milk may also contaminate the cheese making environment and, subsequently, be transferred from the environment to the cheese. Advocates of raw milk may claim that it is perfectly safe, but numerous studies show that several pathogens (such as Campylobacter jejuni, various toxigenic coli, Listeria monocytogenes, several species of Salmonella, and Yersinia enterocolitica) are present at rates as high as 15% of herd milks. After pooling several herds into a tanker and several tankers into a silo, contamination with one or more pathogenic microorganisms is almost certain. Therefore, cheese makers whether large or small, must assume that all raw milk is contaminated with one or more pathogens.
  • Contamination from the cheese making environment is also likely. Listeria monocytogenes is particularly persistent in dairy environments. Canada now has zero tolerance for contamination of RTE (Ready-To-Eat) foods such as cheese with Listeria monocytogenes.

Characterize Hazards

To characterize identified microbial hazards, risk managers ask:

  • How are growth and survival affected by physical conditions such as temperature, acidity measured as pH, water activity (aw), and time?
  • What’s the impact of biological factors such as competition for nutrients or production of antibiotics? For example, many LAB (lactic acid bacteria) produce antimicrobial chemicals.
  • Does the pathogen cause an infection, intoxication, or a toxin mediated infection? For examples: Listeria grows in the gut causing an infection, Staphylococcus produces a toxin that can cause illness even if the bacteria is destroyed, for example, by pasteurization; and enteropathogenic E. coli infect the gut where they produce a toxin, which can cause hemolytic uremic syndrome in children.

As summarized in Table 22.1, all of these factors and others are relevant to cheese safety. A good example of how food properties are used in risk assessment is the change in the Health Canada policy regarding assessment of risk associated with Listeria monocytogenes. In 2011, the pH and aw of foods considered low risk for Listeria were increased to account for new evidence that Listeria was more robust than previously thought. See Table 22.1.

Assess Exposure

The exposure component of risk assessment considers factors that may mitigate or exacerbate risk throughout the entire supply chain of the particular product including distribution, retailing, and food handling during preparation and consumption. The principle pathogenic hurdles during cheese manufacture are summarized in Table 22.4. Again, one of the most useful critical control points for cheese safety is actually a series of points, namely, the profile of pH versus time during cheese manufacture. It is critical that acid development as measured by pH is normal for the particular variety. Typical pH versus time profiles for several cheese varieties are presented in an earlier chapter. See Table 16.1.

Exposure assessment also considers food use data; who is consuming the product and how much are they consuming? This is important because it is never possible to reduce risk to zero. Essentially, exposure assessment looks up and down the supply chain and asks, how much risk remains when this product reaches the consumer? If that product is Camembert or particularly raw milk Camembert where contamination and growth of Listeria and toxigenic E. coli is slightly more probable, then it may be necessary to communicate that risk to vulnerable groups.

Characterize Risk

Improved cheese safety requires variety-specific risk characterization. Effective risk characterization ensures that the data and information gathered during hazard identification, hazard characterization, and exposure assessment, are described in the context of all plant operations and adequately accounted for in risk management protocols. For example, if raw and pasteurized milk are both being used for cheese making in the same facility, potential contamination of pasteurized cheese with raw milk cheese must be understood and mitigated.

4. Risk Communication

Risk communication is active and transparent exchange of knowledge, opinions, and values among all stakeholders. Risk communication includes the following activities.

Training Employees

Managers need to lead the way, ensuring that the company is following best practices, that all supervisors and employees are well trained and motivated to execute the preventative control protocols.

Communicating with Suppliers to Manage Risk

Cheese makers must assess risk associated with all ingredients entering the plant. A high risk ingredient common to all cheese makers is raw milk. Most jurisdictions prescribe raw milk quality standards; cheese makers need to understand and ensure those regulations are met. You also need to identify other criteria specific to your operation. For example, you may specify a lower tolerance for antibiotic residues relative to the official tolerance level.  Substantial risk is also associated with condiments, such as chives, that may be contaminated with pathogenic bacteria.

Communicating with Regulatory and Inspection Agencies

Regulatory agencies are adopting risk based oriented approaches to managing risk. So, effective risk assessment as described in Section 22.5 is critical to understand and effectively implement inspection ready PCPs (Preventative Control Plans). Having said that, the Safe Food for Canadians Act and Regulations is also more outcome based. That means inspectors will be trained to evaluate more holistically allowing more flexibility, for example regarding detailed CCPs, if the cheese maker can demonstrate consistently safe performance with good rationale. For example, several jurisdictions permit sale of cheese curd at room temperature, based on biochemical rationale and historical safety in the absence of definitive challenge studies.

Communicating Risk to Customers and Consumers

No food process is perfectly safe. It is, therefore, important to accurately assess residual risk associated with your cheese products as they leave your plant, and to effectively communicate with customers and consumers about their roles in mitigating residual risk. For example, cheese makers should pay special attention to how their cheese is being handled at deli counters, considering general hygiene, personal hygiene of staff, cross contamination with meats and other cheeses, cleaning of utensils and power slicers, etc.

Cheese labelling to identify residual risk is controversial, but in my view, should be considered. For example, we know that the probability of Listeria monocytogenes is increased on surface mould ripened cheese. So, it may be appropriate to identify that risk on the label or in associated literature or web communications. That communication is more important if the surface mould ripened cheese was made from raw milk.

5. Risk Management

Risk management is policy driven. That policy should, to the extent possible, be consistent with scientific risk assessment, but also needs to consider social and political factors, such as raw milk activists. In the broadest terms, risk management requires a thorough evaluation of risk (yes, that overlaps and is based on the risk assessment), and selection of risk mitigation strategies.

Evaluate Risk

Risk assessment is the first job of risk management. My experience with government and private food safety auditors and inspectors is that they are often challenged by lack of knowledge of particular products and processes, which means that they may have difficulty with the exposure assessment part of risk assessment.

Based on risk assessment, the next part of evaluating cheese risk is to identify higher risk varieties, processes, facilities, and situations.

Select, Implement, and Validate Mitigation Strategies

Finally, the risk manager must rank management priorities considering risk assessment, available technologies and resources, and social, economic, cultural and political factors. Those broad terms include risk management at a high level (e.g., Health Canada). At the plant level, you need to focus on more technical aspects, but you still need to be aware of the socio-economic factors, regulations, etc. that may affect your business and influence food safety policies. In modern practice, risk mitigation tools and protocols are grouped together as Preventative Control Plans (PCP) that consist of good manufacturing practices (GMP) (also known as pre-HACCP), and HACCP type (Hazard Analysis and Critical Control Point) safety assurance protocols.

PCPs deserve more attention than we have time for in this course. Chapter 23 expands on one aspect of PCPs, namely, plant cleaning and sanitation, but the rest of this large topic will have to wait until you meet us online for our comprehensive course entitled, Cheese Safety and Quality Assurance.

Table 22.1: Some factors that affect survival and growth of pathogenic organisms

Factors Description
  • 5.6-7.0, most pathogens grow
  • 4.4-5.6, few pathogens grow but some survive
  • <4.4, 'No' pathogens grow but some may survive
  • 0.9-1.0, most pathogens grow
  • 0.95-0.9, few pathogens grow but some survive
  • <0.85, 'No' pathogens grow but some may
  • survive

Temperature °C
  • <2°C little or no growth, but many pathogens survive
  • 2-10°C some psychrotrophic pathogens such as Listeria can grow

  • 10 – 45°C, most pathogens grow
  • 45 - 55°C, some pathogens may grow and many survive
  • >55°C, little or no growth; some pathogens such as Clostridia spp. and Bacillus cereus will survive; some bacterial toxins such as the notorious Staphylococcus aureus exotoxin survive.
    Cultures Discourage pathogenic growth due to:
    • competition for nutrients and oxygen
    • production of lactic acid (reduced pH)
    • production of bacterial inhibitors
    Salt Addition of salt reduces aw and also has specific affects against bacteria.

    Cheese makers often report salt as a percentage of cheese moisture (SM).

    There is good evidence that SM > 3.5, which is typical for most ripened varieties, inhibits many spoilage bacteria such as coliforms. However, some pathogens such as Listeria are salt tolerant.

    Table 22.2: Some properties of some pathogens associated with cheese

    Organisms Properties
    Listeria monocytogenes
    • Infectious, relatively high doses
    • Cold, acid and salt tolerant
    • Requires full pasteurization
    • Ubiquitous in food environments
    Campylobacter jejuni
    • Infectious, low doses
    Salmonella spp.
    • Infectious, low doses
    Enteropathogenic E. Coli (e.g., 0157 H7)
    • Toxin mediated Infection, low doses
    • Cold and acid tolerant
    • In cheese, usually from milk
    Yersina enterocolitica
    • Psychrotrophic
    Staphylococci aureus
    • Intoxication; illness caused by exotoxin
    • In cheese, usually from people contact

    Table 22.3: Health Canada Policy on Listeria monocytogenes in ready-to-eat foods: maximum pH and Aw for classification as lower risk RTE foods

    Before (under 2004 policy) Now (2011 version)
    • pH < 5, or
    • Aw ≤ 0.92, or
    • pH < 5.5 & Aw < 0.95, or
    • Refrigerated for ≤ 10 days
    • Unchanged: Frozen until consumption RTE products
    • pH < 4.4, or
    • Aw < 0.92, or
    • pH < 5 & Aw <0.94, or
    • Refrigerated for ≤ 5 days
    • Unchanged: Frozen until consumption RTE products

    Table 22.4: Hurdles to growth and survival of pathogenic bacteria in cheese making

    Cold storage of milk Slows or stops growth of both pathogens and competitors. Cold tolerant spoilage bacteria such as species of Pseudomonas will tend to dominate in cold stored milk. Many pathogenic organisms will but not grow during cold storage but will survive.
    Standardize microflora Microfiltration and pasteurization reduce pathogenic bacteria. Some spore forming pathogens, such as Bacillus cereus may be encouraged by pasteurization.
    Cultures Cultures produce antimicrobials and reduce pH. The pH versus time profile is the most useful quality control and safety assurance tool for the cheese maker.
    Water activity (aw) The aw is not a limiting factor except in drier and aged cheese, such as hard Italian cheese. Aw in aged Cheddar (+3 years) may decrease below 0.90 which reduces growth of pathogens. Salt is also preservation factor.
    Temperature history E.g., Pathogen survival is dramatically reduced in thermophilic cheeses ‘cooked’ up to 55°C, typically for 30 minutes.
    Exposure history Cheese is often exposed to the plant environment and often to human contact for considerable periods of time, especially in traditional operations. On the other hand, automated curd handling and filling systems are difficult to clean.

    Hard Italian types of cheese are good examples because they are cooked (52 - 55°C) and then immediately transferred while still hot into the forms, so environmental contamination after the kill step (cooking) is minimal relative to Cheddar which is exposed to the environment for several hours before forming. Exposure to the environment is especially critical for fresh cheeses such as Latin American Panela cheese. Similarly it is critical to cover heat-acid cheeses while they are still hot.

    Exposure during presentation, cutting and wrapping in delis is also important, because environmental contamination and cross contamination from other cheese and other products such as sliced meat is possible.

    Ripening time Pathogens decline due to low pH, decreasing aw, antimicrobials, and low oxygen


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