Once you've identified your critical control points, the next vital step in the HACCP system is establishing precise critical limits for each CCP. Critical limits serve as the boundaries between safe and unsafe food production, acting as measurable thresholds that must be maintained to ensure food safety hazards are effectively controlled.
A critical limit is defined as "a maximum and/or minimum value to which a biological, chemical or physical parameter must be controlled at a CCP to prevent, eliminate or reduce to an acceptable level the occurrence of a food safety hazard". Indeed, these limits distinguish between what's acceptable and what could lead to unsafe food.
Setting Scientific basis for critical limits
Critical limits must be established on solid scientific foundations. Without science-backed parameters, your HACCP plan lacks credibility and effectiveness. Typically, food businesses derive their critical limits from several authoritative sources:
- Scientific research and peer-reviewed publications
- Regulatory requirements and guidelines (FDA, USDA, Codex Alimentarius)
- Industry standards and best practices
- Expert consultation (food scientists, microbiologists, process authorities)
- In-house validation studies with proper documentation
Most importantly, critical limits aren't arbitrary values; they represent scientifically validated thresholds where hazards are effectively controlled. For instance, the critical limit for cooking beef burgers specifies that the center must reach a minimum temperature of 75°C to destroy pathogens. This value isn't chosen randomly but based on extensive microbiological research demonstrating pathogen destruction at this temperature.
Critical limits should never be copied from similar processes without validation, as each food operation has unique characteristics that may affect hazard control. Furthermore, these limits must be observable and measurable in real-time during production to allow for immediate corrective actions if deviations occur.
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Common parameters
Several parameters commonly serve as critical limits in HACCP plans based on their significant impact on microbial growth and survival:
Temperature
Temperature remains one of the most frequently used critical limits. For thermal processes like cooking or pasteurization, time-temperature combinations are crucial. For example, milk pasteurization requires 63°C for 30 minutes or 72°C for at least 15 seconds. Similarly, refrigeration temperature limits (typically below 5°C) prevent pathogen growth during storage.
pH Level
pH level is another vital parameter affecting microbial growth. Many pathogens cannot grow in acidic environments below certain pH levels. The pH threshold of 4.6 is particularly significant as it prevents Clostridium botulinum growth in acidified foods. Nevertheless, recent changes to some food codes have lowered this threshold to 4.2 for certain troublesome strains.
Water activity
Water activity (aw) measures the available water microorganisms can use for growth. Water activity works on a scale from 0 (no water) to 1 (pure water). Notably, most bacteria cannot grow at water activity below 0.85, making this an important critical limit for many shelf-stable foods. Clostridium botulinum specifically cannot grow at water activity below 0.93.
Other parameters that may serve as critical limits include:
- Salt or sugar concentration
- Moisture content
- Product dimensions
- Flow rate or belt speed in continuous processes
- Metal fragment size in detection systems
- Sanitizer concentration
- Validation of critical limits
Establishing critical limits isn't enough; they must be validated to ensure they actually work in practice. Validation involves obtaining evidence that a control measure, if properly implemented, can control the hazard to the specified outcome.
Practical Examples of Critical Limits
| Industry | Process Step (CCP) | Hazard Controlled | Critical Limit | Monitoring Tool |
| Dairy (milk processing) | Pasteurization | Listeria, Salmonella | Minimum 72°C for 15 seconds (HTST) then rapid cooling | Temperature-time recorder |
| Catering (chicken cooking) | Cooking | Salmonella, Campylobacter | Internal/ core temperature ≥75°C for 1 minute | Calibrated probe thermometer |
| Bottled juice | pH control | Clostridium botulinum | pH ≤ 4.5 | Calibrated pH meter |
| Fresh-cut salad | Chlorinated wash | E. coli, Norovirus | Free chlorine 50–200 ppm, contact time ≥60 seconds | Chlorine test strips or meter |
| Bottling line | Metal detection | Physical hazards | Detects ferrous ≥2.0 mm, non-ferrous ≥2.5 mm, stainless ≥3.5 mm | Daily calibration checks with test pieces |
| Ready meals | Cooling | Clostridium perfringens | Cool from 65°C to 5°C within 2 hours | Temperature log & timer |
| Ice cream production | Mix pasteurization | Listeria, Salmonella | 80°C for 25 seconds then rapid cooling | Batch pasteurizer recorder |
| Poultry Processor | Blast Freezing of Chicken | Campylobacter, Salmonella | Chicken must reach core temperature of -18°C within 6 hours | Temperature log & timer |
| Bakery Products | Filled pastries / bakery snacks with cream or jam filling | Staphylococcus aureus, molds, yeasts | Water activity must be ≤ 0.85 | Calibrated water activity meter |
There are two essential components to critical limit validation:
- Theoretical validation confirms that the selected critical limits are scientifically sound. This involves gathering reliable information from regulatory requirements, scientific literature, or expert consultation.
- Process capability validation demonstrates that your operation can consistently achieve the established critical limits, even under worst-case scenarios.
Validation should occur before implementing your HACCP plan and whenever significant changes are made to your process. For instance, if you establish a critical cooking temperature of 75°C for chicken, you must validate that your cooking equipment consistently achieves this temperature throughout the product under various operating conditions.
Undoubtedly, proper validation prevents food safety failures by ensuring your critical limits actually control the identified hazards. As the FDA notes, critical limits "must be scientifically based" to ensure they're capable of controlling hazards to an acceptable level.
Critical limits vs operational limits
Critical limits differ from operational limits. While critical limits are safety-focused boundaries separating safe from unsafe products, operational limits are often more stringent internal targets set to provide a safety cushion. For example, if your critical limit for cooler temperature is 5°C, you might set an operational target of 3°C to provide a margin of safety.
Ultimately, well-established and properly validated critical limits form the backbone of your HACCP system, ensuring your food safety controls are both effective and scientifically sound.
Examples from industry
Case 1: Swiss Roll Cake Factory – KSA
- Hazard: Staphylococcus aureus growth in cream filling during storage
- CCP step: water activity check after mixing cream and before filling
- Critical limit: water activity must be ≤ 0.85
- Corrective action: Reformulate with more sugar/drying if water activity too high
- Result: Enabled safe ambient-temperature storage for 14 days without preservatives.
Case 2: Date-Filled Cookies Manufacturer – UAE
- Hazard: Mold and yeast growth in moist date filling
- Critical limit: Water activity of date paste must be ≤ 0.75
- Monitoring: Water activity meter check on each batch of filling
- Result: Controlled spoilage, extended shelf life from 4 weeks to 8 weeks, and reduced product returns by 60%.
Read more about Understanding HACCP Principle 1: Conduct a Hazard Analysis.
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