Preservation, packaging, chilling, freezing and shelf-life
Scope
This domain tests chilling, freezing, packaging and shelf-life: how to slow or stop microbial growth and quality loss, and how to prove a shelf-life claim.
Core rules
- The danger zone is 5–63 °C. Cook-chill products should be cooled from 63 °C to 5 °C within 90 minutes (UK guidance) and held at 0–5 °C.
- Freezing at -18 °C stops microbial growth but does not kill pathogens; thawing must be controlled.
- MAP replaces oxygen or modifies gas composition. It does not replace temperature control; anaerobic pathogens such as Clostridium botulinum remain a concern.
- Water activity, pH, salt, nitrite and thermal processing are hurdles. Combine hurdles rather than relying on one.
- Shelf-life should be supported by challenge testing, predictive microbiology or durability studies, not guesswork.
Worked example
A 10 kg batch of sauce must be chilled from 75 °C to 5 °C. Sensible heat removed ≈ 10 kg × 4.18 kJ/kg°C × 70 °C = 2,926 kJ. A chiller removing 0.5 kW (0.5 kJ/s) needs 5,852 s ≈ 98 minutes, before accounting for container and evaporative losses. That fails a 90-minute target; choose a faster chiller or smaller batch.
Traps
- Believing freezing sterilises food.
- Using MAP without a cold chain.
- Quoting shelf-life from a single sample.
- Ignoring condensation and post-process contamination.