Nut Processing

Nut processing facilities require specialized refrigeration and environmental control to manage heat loads from roasting operations, prevent oxidative rancidity, and maintain product quality through blanching, coating, and packaging stages. The high oil content in nuts makes temperature and humidity control critical for shelf life extension.

Roasting Cooling Requirements

Post-roasting cooling systems must rapidly reduce nut temperatures from 140-175°C to packaging temperatures while preventing moisture condensation and oil migration.

Cooling System Design

Fluidized Bed Cooling:

• Air velocity: 150-250 m/min through product bed
• Cooling air temperature: 10-15°C
• Cooling time: 3-8 minutes depending on nut size
• Air volume: 2000-3500 m³/h per ton of nuts
• Heat removal: 350-450 kJ/kg for roasted peanuts
• Temperature reduction: 150°C to 30-35°C

Belt Cooling Conveyors:

• Conveyor length: 12-20 meters for adequate residence time
• Air temperature: 12-18°C supply air
• Air velocity: 100-180 m/min perpendicular to product flow
• Product layer depth: 25-50 mm maximum
• Cooling capacity: 120-180 kW per ton/hour throughput

Rotary Drum Coolers:

• Drum rotation: 8-15 RPM
• Cooling air flow: concurrent or countercurrent configuration
• Air temperature: 8-15°C for rapid cooling phase
• Heat transfer coefficient: 25-40 W/m²·K
• Residence time: 10-15 minutes

Cold Storage for Rancidity Prevention

Refrigerated storage inhibits lipid oxidation and extends shelf life by reducing enzyme activity and preventing oil degradation in high-fat nuts.

Storage Temperature Requirements

In-Shell Storage:

• Temperature: 0-4°C for tree nuts, 2-7°C for peanuts
• Relative humidity: 65-70% to prevent kernel moisture gain
• Air circulation: 0.5-1.0 air changes per hour
• Storage duration: 12-18 months at optimal conditions
• Respiration heat: 0.05-0.12 W/ton (minimal compared to processing loads)

Shelled Nut Storage:

• Temperature: -1 to 2°C for maximum shelf life
• Relative humidity: 55-65% to maintain 3-6% moisture content
• Air velocity: <0.5 m/s to prevent surface drying
• Oxygen levels: <2% for inert atmosphere storage (premium products)
• Storage capacity: 150-200 kg/m³ bulk density

Frozen Storage (Extended Shelf Life):

• Temperature: -18 to -23°C
• Product core temperature: -18°C minimum
• Freezing rate: slow freezing acceptable (no cellular damage concern)
• Storage duration: 24-36 months without quality degradation
• Defrosting: controlled at 4-8°C to prevent condensation

Blanching and Coating Cooling

Thermal blanching and coating processes introduce heat loads requiring immediate refrigeration to prevent over-processing and maintain coating adhesion.

Blanching Cooling Systems

Water Blanching:

• Blanching temperature: 95-100°C for 60-180 seconds
• Cooling water temperature: 1-4°C
• Cooling water flow: 3-5 L/kg nuts processed
• Heat removal: 280-340 kJ/kg (sensible heat only)
• Chiller capacity: 80-120 kW for 1000 kg/h operation
• Water recirculation: 85-90% with continuous chilling

Steam Blanching:

• Steam temperature: 100-105°C (atmospheric pressure)
• Post-blanch temperature: 70-85°C
• Cooling air temperature: 4-8°C
• Air velocity: 200-300 m/min for rapid surface cooling
• Moisture removal: 15-25% reduction during cooling
• Refrigeration load: 60-90 kW per ton/hour throughput

Coating Process Cooling

Chocolate Coating:

• Pre-coat nut temperature: 18-22°C (critical for adhesion)
• Post-coat cooling tunnel temperature: 8-12°C
• Cooling tunnel length: 15-25 meters
• Belt speed: 2-5 m/min
• Cooling time: 3-5 minutes for shell crystallization
• Refrigeration capacity: 40-60 kW per coating line

Yogurt/Candy Coating:

• Coating temperature: 40-50°C
• Cooling air temperature: 10-15°C
• Relative humidity: 35-45% to prevent surface stickiness
• Air velocity: 150-250 m/min
• Cooling duration: 4-8 minutes
• Dehumidification load: 3-5 kg water/hour per line

Humidity Control

Moisture content management prevents oil separation, maintains crispness, and ensures coating adhesion in processed nut products.

Moisture Equilibrium

Critical Moisture Ranges:

• Roasted nuts: 1.5-3.0% moisture for optimal crispness
• Raw nuts in-shell: 6-9% moisture for storage stability
• Blanched nuts: 2.5-4.5% after drying
• Coated products: 2.0-3.5% in nut center
• Water activity (aw): 0.20-0.40 for shelf-stable products

Dehumidification Systems

Desiccant Dehumidification:

• Process air dew point: -10 to -20°C
• Regeneration temperature: 120-140°C
• Air flow rate: 1500-2500 m³/h per ton/hour production
• Moisture removal: 4-8 kg water/hour
• Energy consumption: 2.8-3.5 kWh/kg water removed

Refrigerant Dehumidification:

• Evaporator temperature: 0-3°C
• Supply air temperature: 12-16°C
• Relative humidity control: ±3% setpoint
• Cooling coil capacity: 45-70 kW per processing zone
• Latent heat ratio: 0.35-0.50 (moderate latent load)

Packaging Room Conditions:

• Temperature: 18-22°C
• Relative humidity: 40-50%
• Air changes: 10-15 per hour with HEPA filtration
• Pressurization: +10 Pa relative to adjacent areas
• Dew point: 5-10°C maximum

System Integration Considerations

Heat Recovery Applications:

• Roaster exhaust heat recovery: 40-60% of combustion energy
• Refrigeration condenser heat: blanching water preheating to 40-50°C
• Compressor heat: building heating or hot water generation
• Overall energy reduction: 15-25% with integrated heat recovery

Refrigeration System Selection:

• Ammonia (R-717) for large cold storage facilities (>500 ton capacity)
• R-404A or R-448A for process cooling applications
• Glycol secondary loops for blanching water chilling
• Variable speed compressors for fluctuating process loads
• Heat reclaim condensers for 60-80% heat recovery efficiency

Process Sequencing:

• Pre-cooling roasted nuts before coating prevents coating melting
• Humidity stabilization period (30-60 minutes) before packaging
• Temperature equalization in cold storage before shipping
• Continuous monitoring of nut core temperature during processing

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