SOP-003: Freeze-Thaw Cycling

1. Purpose

This procedure establishes the protocol for freeze-thaw cycling to evaluate emulsion stability under thermal stress conditions. This test stresses emulsifier systems, water binding, preservative partitioning, and container integrity.

2. Scope

This SOP applies to all emulsion-based cosmetic products, particularly those that may be exposed to temperature fluctuations during shipping or storage.

3. Cycle Conditions

Phase	Temperature	Duration
Freeze	-10°C to -20°C (14°F to -4°F)	24 hours minimum
Thaw	20-25°C (68-77°F)	24 hours minimum

Complete Cycle: One freeze + one thaw = 48 hours minimum

Recommended Cycles: 3 to 6 cycles (6-12 days total)

4. Equipment Requirements

Freezer capable of reaching -20°C
Thermometer or temperature logger
Timer or scheduling system
Ambient storage area (20-25°C)

5. Sample Requirements

Minimum 2 units per batch
Samples in final market packaging
Retain control sample at ambient for comparison
Leave headspace in container (product expands when frozen)

6. Procedure

Record initial appearance, texture, and any observations at T0
Place samples in freezer, ensuring temperature reaches target
After 24 hours freeze, move samples to ambient storage
After 24 hours thaw, evaluate samples at room temperature
Record observations for each cycle
If product re-emulsifies with gentle shaking, note this
Repeat for specified number of cycles
Final evaluation after last thaw cycle

7. Evaluation Parameters

7.1 Phase Separation

Look for: oil/water separation, creaming, sedimentation, syneresis

7.2 Texture Changes

Evaluate: grittiness, graininess, thickening, thinning, loss of smoothness

7.3 Re-emulsification

Test if product returns to original state with gentle shaking. Note if mixing is required.

7.4 Container Integrity

Check for: leaks, cracks, pump failure, label damage

Note: Microbes can survive freeze-thaw conditions. A product that fails freeze-thaw testing may become microbiologically vulnerable after structural damage, even if no immediate microbial growth is visible.

Product Name:
Batch/Lot Number:
Test Start Date:
Freeze Temperature:	_______°C
Thaw Temperature:	_______°C
Number of Cycles:

Cycle	Date Completed	Appearance	Separation?	Texture Change?	Re-emulsifies?	Pass/Fail	Initials
Before (T0)
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
Cycle 6