3.1 Definition
Time temperature tolerances (TTT’s) refer to the total time that a refrigerated perishable product can be without cooling during handling and loading. This includes the total cumulative time during breaks in the cold chain. TTT’s are based on product requirements, not logistical processes, and are intended to account for operational inadequacies.
3.2 Effect of Temperature Fluctuations
- Increases in temperature for both chilled and deep frozen perishable products can negatively affect product quality, eating quality, food safety, and appearance.
- Fresh produce remains metabolically active; higher temperatures accelerate ripening and moisture loss.
- Microbiological spoilage increases with temperature in both fresh and frozen produce.
- Fluctuating temperatures cause condensation on packaging and product, leading to microbiological growth (rots and decay) or ice formation in deep frozen produce.
- Maintaining constant temperatures is essential once the cold chain is initiated, though not always possible during transfers or handling.
- Maximum exposure times and temperature increases that can be tolerated are specified as TTT’s, which may vary by product, ambient conditions, handling method, and equipment.
- TTT’s for various products are defined in PPECB Handling Procedure documents (ISO 9001-2000 system).
- Important criteria for TTT calculation include:
- Inherent product requirements (e.g., degreened citrus, maturing pears)
- Effect of increased temperature on fruit ripening (e.g., avocado, mango)
- Effect on condensation and frost formation (e.g., polybag grapes, frozen produce)
- Efficiency of refrigeration unit to recool product
- Cooling rate of carton and pallet (ventilation and position)
3.3 Specific Product Requirements
- Deciduous and citrus fruit:
Maximum TTT is 6 hours (time for center of pallet fruit to show a temperature increase), considering respiration and packaging. - Subtropical fruit:
Maximum TTT is 3 hours (time to create a 1.0°C differential between coldest and warmest fruit on the same pallet). - Deep frozen produce:
International requirement: maximum increase of 3°C in the warmest position during transfer from cold store to refrigerated deck. Product must be recooled to the specified carrying temperature before loading. - Other products:
Maximum TTT of 6 hours applies to most less temperature-sensitive products. Keep TTT as short as possible to avoid condensation, which increases fungal/bacterial waste and can damage packaging.
3.4 General TTT Breakdown per Action
3.1.1 Container Handling – Deciduous and Citrus Fruit
| Action | 6 hour TTT | 3 hour TTT |
|---|---|---|
| Loading container out of cold store | 1 hour | 1 hour |
| Transport to port terminal | 2 hours | |
| Handling in port terminal | 1 hour | 1 hour |
| Loading onto vessel | 2 hours | 1 hour |
| Total | 6 hours | 3 hours |
3.1.2 Conventional Deck Loading
- Impractical to measure/apply TTT’s during loading of conventional decks.
- Rule: Maximum pulp temperature increases apply.
- Decks must be closed and recooling started as soon as the following pulp temperatures are reached:
- All fruit not packed in polyethylene bags: [temperature not specified]
- Subtropical fruit: 12°C
- All subtropical: 5°C above the temperature
- All fruit packed in polyethylene bags: 8°C
- Pulp temperature in center of pallets: No increase allowed