Quality Deterioration During Storage

Egg quality deteriorates continuously from the moment of lay through storage and distribution. The rate of deterioration is governed by temperature, relative humidity, air composition, and storage duration. Understanding these mechanisms is critical for designing refrigeration systems that minimize quality loss while maintaining economic viability.

Fundamental Deterioration Mechanisms

Physical Changes During Storage

Moisture Loss Through Shell

• Water vapor transmission through shell pores
• Driven by vapor pressure difference between egg interior and ambient air
• Rate proportional to (P_egg - P_ambient) and shell permeability
• Typical loss: 0.01-0.02% per day at 0°C, 60-70% RH
• Shell permeability increases with egg age and washing

Air Cell Enlargement

• Direct consequence of moisture loss
• Air cell grows as internal volume decreases
• Provides bacteria entry point when shell membrane dries
• USDA grading based on air cell depth

Albumen Thinning

• Thick albumen converts to thin albumen over time
• Ovomucin-lysozyme complex degradation
• pH-dependent reaction accelerated by temperature
• Loss of gel structure reduces Haugh unit

Yolk Membrane Weakening

• Vitelline membrane loses elasticity
• Water migration from albumen to yolk
• Yolk flattens, increases in diameter
• Eventually leads to membrane rupture

Chemical Deterioration Processes

Carbon Dioxide Loss

• Fresh eggs contain 3-5% CO2 by volume
• CO2 diffuses through shell pores
• Loss rate: k_CO2 = A × exp(-E_a / RT)
• Half-life at 4°C approximately 14-21 days
• CO2 loss raises albumen pH from 7.6 to 9.0-9.4

pH Changes and Consequences

Protein Denaturation

• Accelerated at elevated pH
• Ovomucin complex dissociates
• Lysozyme activity decreases
• Functional properties degraded

Haugh Unit Decline Kinetics

Haugh Unit Definition

The Haugh unit (HU) quantifies egg interior quality based on albumen height and egg weight:

HU = 100 × log(H - 1.7W^0.37 + 7.6)

Where:

• H = albumen height (mm) measured from highest point of thick white
• W = egg weight (g)

Quality Classifications:

Temperature-Dependent Deterioration Rates

Haugh unit decline follows first-order kinetics with temperature dependence described by Arrhenius relationship:

dHU/dt = -k × HU

k = k_0 × exp(-E_a / RT)

Where:

• k = deterioration rate constant (day^-1)
• k_0 = pre-exponential factor
• E_a = activation energy (approximately 85-95 kJ/mol)
• R = universal gas constant (8.314 J/mol·K)
• T = absolute temperature (K)

Typical Decline Rates:

Predictive Model for Haugh Unit

HU(t) = HU_0 × exp(-kt)

For variable temperature storage:

HU(t) = HU_0 × exp(-∫k(T)dt)

Example Calculation:

• Initial HU = 95
• Storage at 4°C for 21 days
• k = 0.015 day^-1
• HU(21) = 95 × exp(-0.015 × 21) = 95 × 0.732 = 69.5

Result: Downgraded from AA to B grade in three weeks.

Moisture Loss and Weight Reduction

Vapor Pressure Driving Force

Rate of moisture loss = k_mass × A × (P_sat(T_egg) - RH × P_sat(T_air))

Where:

• k_mass = mass transfer coefficient (kg/m²·s·Pa)
• A = effective shell surface area (m²)
• P_sat = saturation vapor pressure (Pa)
• RH = relative humidity (decimal)

Shell permeability factors:

• Pore density: 7,000-17,000 pores per egg
• Pore diameter: 10-50 μm
• Shell thickness: 0.3-0.4 mm
• Cuticle integrity (washing removes protective layer)

Weight Loss Data

Economic Impact:

• 60 dozen case weighs approximately 36 kg (80 lb)
• At 0.5% loss over 30 days: 180 g (0.4 lb) per case
• For 10,000 cases: 1,800 kg (4,000 lb) shrinkage
• At $3/kg wholesale: $5,400 loss

Optimal Humidity Control

Target relative humidity: 70-80%

Below 70% RH:

• Excessive moisture loss
• Rapid air cell growth
• Economic shrinkage losses
• Shell membrane drying

Above 85% RH:

• Condensation on shell surface
• Bacterial growth promotion
• Mold development
• Shell penetration risk

Temperature Abuse Consequences

Acute Temperature Exposure

Single temperature abuse event:

ΔHU_abuse = HU_before - HU_after = HU_before × (1 - exp(-k_abuse × t_abuse))

Example scenarios:

Cumulative Temperature History

Time-Temperature Tolerance (TTT) approach:

Quality Index = Σ(t_i × k(T_i))

Where sum is over all time intervals with different temperatures.

Critical threshold values:

Temperature Monitoring Requirements

Continuous monitoring essential:

• Data loggers with 5-15 minute intervals
• Alert thresholds at ±1°C from setpoint
• Cumulative degree-hour tracking
• Automated quality prediction systems

Corrective actions for temperature excursions:

• Immediate assessment of exposure duration
• Quality testing of representative samples
• Segregation of affected inventory
• Accelerated distribution to processing

Carbon Dioxide Depletion Effects

CO2 Loss Mechanism

Diffusion rate through shell:

dm_CO2/dt = -D_eff × A × (C_inside - C_outside) / L

Where:

• D_eff = effective diffusivity through shell (m²/s)
• A = shell surface area (m²)
• C = CO2 concentration (mol/m³)
• L = effective diffusion path length (m)

Temperature effect on CO2 loss:

Albumen pH Rise

CO2 content correlates with pH:

pH = 7.6 + 2.1 × (1 - C_CO2/C_CO2,initial)

pH effects on albumen quality:

Modified Atmosphere Storage

CO2-enriched storage:

• Atmosphere: 2-5% CO2, balance air
• Maintains lower albumen pH
• Extends Haugh unit retention
• Requires gas-tight containers
• Cost-benefit favors long storage periods

Performance comparison (30 days storage @ 4°C):

Quality Monitoring and Control Strategies

Sampling and Testing Protocols

Statistical sampling plans:

• Minimum 30 eggs per lot for reliable HU measurement
• Random selection from multiple cases
• Temperature verification at sampling
• Record storage history and handling

Test frequency:

Predictive Quality Management

Mathematical model integration:

Predicted HU = f(HU_initial, T(t), RH(t), t)

Model inputs:

• Initial quality at lay (HU_0 = 90-100)
• Complete temperature profile from sensors
• Relative humidity history
• Storage duration

Decision support outputs:

• Predicted current Haugh unit
• Estimated remaining shelf life to grade limits
• Optimal distribution timing
• Temperature setpoint optimization

HVAC System Design Implications

Precision temperature control requirements:

Air distribution critical factors:

• Minimize temperature stratification (<1°C vertical gradient)
• Uniform air velocity (0.15-0.25 m/s across pallets)
• Avoid direct impingement on egg flats
• Perforated cases require careful airflow management

Humidity control integration:

• Direct injection steam humidification
• Evaporative pad systems (risk of contamination)
• Ultrasonic atomization (fine control)
• Continuous monitoring and feedback control

Quality-Based Storage Duration Guidelines

Maximum Storage Periods by Grade

Recommended maximum storage to maintain grade:

Factors requiring reduced storage:

• High initial temperature at lay (>30°C ambient)
• Extended time before cooling (>12 hours)
• Mechanical damage to shells
• Previous temperature abuse
• Washed eggs (cuticle removed)

First-In-First-Out (FIFO) Management

Age-based inventory rotation:

• Electronic tracking of lay date
• Automated warehouse management systems
• Visual lot identification (color coding)
• Physical segregation by age groups

Quality-based adjustments:

• Periodic quality testing overrides age alone
• Temperature history affects rotation priority
• Abuse-exposed lots moved to immediate use

Economic Optimization

Value Loss Functions

Market value as function of quality:

V(HU) = V_max × [1 - k_v × (HU_max - HU)²]

Where:

• V_max = maximum value (AA grade price)
• k_v = value depreciation coefficient
• HU_max = typical maximum (95-100)

Price differentials (example market):

Refrigeration Cost vs. Quality Retention

Total cost optimization:

TC = C_energy × t + (V_initial - V_final) × N

Where:

• C_energy = refrigeration operating cost per day
• t = storage duration
• V_initial, V_final = value per egg at start and end
• N = number of eggs

Example calculation:

• 360,000 eggs (10,000 dozen)
• Storage at 4°C vs. 10°C for 30 days
• Energy cost difference: $0.08/day higher for 4°C
• Total energy cost difference: $2.40
• Value retention difference: $0.15/dozen × 10,000 = $1,500
• Net benefit of 4°C storage: $1,497.60

Conclusion: Precision temperature control pays for itself through quality retention.

Summary

Egg quality deterioration during refrigerated storage is governed by temperature-dependent chemical and physical processes. Haugh unit decline follows exponential kinetics with rate constants increasing dramatically with temperature. Moisture loss and CO2 depletion compound quality degradation. Precision HVAC control at 0-4°C with 70-80% RH minimizes deterioration rates and maximizes economic returns. Continuous monitoring, predictive modeling, and rapid inventory rotation optimize quality delivery while controlling refrigeration costs.