Juice Processing

Juice processing refrigeration systems provide thermal control for extraction, pasteurization, concentration, and storage operations. Temperature management preserves nutritional quality, prevents enzymatic degradation, and controls microbial growth throughout the production chain.

Processing Temperature Requirements

Different juice types and processing stages demand specific thermal conditions:

Flash Cooling Systems

Flash cooling rapidly reduces juice temperature immediately post-pasteurization to prevent thermal degradation while maintaining aseptic conditions.

Plate Heat Exchanger Design: Flash cooling employs multi-stage plate heat exchangers with glycol or ammonia refrigerant circuits. Thermal shock from 90-95°C to 2-4°C occurs within 10-30 seconds, requiring heat removal rates of 300-500 kW per 10,000 L/h production capacity.

Heat removal calculation: Q = ṁ × cp × ΔT

For orange juice (cp = 3.85 kJ/kg·K, ρ = 1045 kg/m³):

• Production rate: 10,000 L/h = 2.91 kg/s
• Temperature drop: 92°C to 3°C = 89 K
• Heat load: Q = 2.91 × 3.85 × 89 = 997 kW

Cooling Medium Selection:

Plate spacing of 3-5 mm maintains turbulent flow (Re > 4000) while preventing pressure drops exceeding 70-100 kPa. Stainless steel 316L construction resists organic acid corrosion from citric and malic acids.

Pasteurization Heat Recovery

Energy recovery from hot pasteurized juice preheats incoming raw juice, reducing heating and cooling loads by 70-85%.

Regeneration Section Performance:

Regeneration efficiency (η) relates to the temperature rise of cold juice: η = (T_cold,out - T_cold,in) / (T_hot,in - T_cold,in)

Typical performance for 10,000 L/h system:

• Raw juice inlet: 15°C
• After regeneration: 75°C
• Pasteurization: 90°C
• Regeneration efficiency: 82%
• Heating reduction: 75 kW vs. 365 kW (without recovery)
• Cooling reduction: 665 kW vs. 997 kW (without recovery)

Concentrate Production Refrigeration

Evaporative concentration removes water at reduced pressure and temperature, requiring substantial refrigeration for vapor condensation and product cooling.

Multi-Effect Evaporator Loads:

Total refrigeration for 10,000 L/h single-strength to 65°Brix concentrate: 930 kW.

Vapor Condensing Systems: Surface condensers operate at 2-8°C to condense water vapor from final evaporator effects. Ammonia or R-507A refrigeration provides chilled water at 1-3°C, with approach temperatures of 2-4 K.

For fourth effect at 6 kPa absolute:

• Vapor saturation temperature: 37°C
• Condensing temperature required: 33°C
• Chilled water supply: 3°C
• Return temperature: 10°C
• Heat exchanger area: 45-60 m² per 1000 kg/h vapor

Aseptic Processing Systems

Aseptic juice processing combines ultra-high temperature (UHT) treatment with sterile cooling and filling, extending shelf life to 6-12 months without refrigeration until opened.

UHT Flash Cooling Requirements:

UHT processing heats juice to 135-145°C for 2-4 seconds, then flash cools to 20-25°C for ambient filling or to 2-4°C for cold fill operations.

Heat removal rate:

• UHT exit temperature: 138°C
• Flash cooling target: 22°C
• Temperature drop: 116 K
• For 5000 L/h production: Q = 1.45 × 3.85 × 116 = 647 kW

Multi-stage cooling sequence:

1. Regeneration section: 138°C → 50°C (heat recovery)
2. Chilled water stage: 50°C → 30°C (250 kW)
3. Glycol stage: 30°C → 22°C (120 kW)

Cold Storage Refrigeration

Bulk juice storage maintains quality between processing and packaging or during market distribution delays.

Storage Tank Cooling Systems:

Tank cooling load components:

1. Product pulldown: ṁ × cp × ΔT
2. Infiltration losses: U × A × ΔT (insulated tanks)
3. Agitation heat: Motor kW × efficiency factor
4. Ambient transmission: Through walls, roof

For 25,000 L fresh orange juice tank:

• Pulldown: 25,000 kg × 3.85 kJ/kg·K × 18 K / 4 h = 481 kW average
• Transmission (R-25 walls): 0.23 W/m²·K × 50 m² × 23 K = 265 W
• Agitation: 5.5 kW motor × 0.15 heat factor = 825 W
• Total refrigeration: 25-30 kW (peak), 5-8 kW (maintenance)

Enzymatic Activity Control

Refrigeration slows enzymatic degradation that causes cloud loss, color changes, and off-flavor development.

Critical Enzyme Systems:

Reaction rate temperature dependence follows Arrhenius relationship: k = A × e^(-Ea/RT)

Q₁₀ values (reaction rate change per 10°C) for juice enzymes range from 1.8 to 3.5. Refrigeration from 20°C to 2°C reduces enzymatic activity by factor of 8-15, extending quality retention from hours to days.

Microbial Growth Prevention

Temperature control inhibits pathogenic and spoilage microorganisms throughout processing and storage.

Microbial Control Temperatures:

Combined pasteurization and refrigeration provides multiple hurdles. Flash cooling to <4°C within 30 minutes post-pasteurization prevents spore germination and outgrowth of surviving heat-resistant organisms.

System Design Considerations

Refrigeration Capacity Factors:

Total installed capacity includes safety factors for:

• Product pulldown: 1.2-1.5× calculated load
• Ambient conditions: 1.1-1.3× for summer peaks
• Fouling degradation: 1.15-1.25× over cleaning cycles
• Future expansion: 1.2-1.4× planned capacity

Typical juice plant refrigeration distribution:

• Flash cooling: 35-45% of total capacity
• Concentrate production: 25-35%
• Cold storage: 15-25%
• Process auxiliaries: 5-10%

Glycol System Design: Central glycol systems serve multiple heat exchangers with 30-40% propylene glycol solution at -8 to -2°C supply temperature. Pumping rates of 0.05-0.08 L/s per kW cooling load maintain 4-6 K temperature differentials.

Glycol circulation pump power: P = (ΔP × V̇) / (η_pump × η_motor)

For 1000 kW cooling load:

• Flow rate: 60 L/s
• Pressure drop: 150 kPa
• Pump power: (150 × 0.06) / (0.75 × 0.92) = 13 kW

Ammonia Direct Expansion: Large capacity installations (>500 kW) employ ammonia DX systems with plate evaporators or shell-and-tube chillers. Evaporator temperatures of -10 to -6°C produce glycol at -5 to -2°C with approach temperatures of 3-5 K.

Ammonia charge minimization strategies:

• Liquid overfeed with gravity return
• Pumped recirculation at 3-4:1 ratio
• Falling film evaporators
• Plate frame heat exchangers (minimal charge)

Energy Efficiency Measures

Heat Recovery Integration:

1. Pasteurization regeneration: 75-85% energy recovery
2. Evaporator vapor recompression: 40-60% steam reduction
3. Condensate heat recovery: 5-10% auxiliary heating
4. Refrigeration heat reclaim: Pasteurization preheating, CIP water heating

Variable Capacity Control:

• Variable frequency drives on refrigeration compressors
• Multiple evaporator stages with sequencing
• Floating head pressure control (ambient tracking)
• Demand-based glycol pumping

Annual energy consumption for 10,000 L/h juice plant:

• Refrigeration: 1,200,000 kWh (60% of total)
• Heating: 600,000 kWh (30%)
• Pumping/mixing: 200,000 kWh (10%)

Heat recovery reduces consumption by 450,000-600,000 kWh annually, with payback periods of 1.5-3.5 years for regeneration systems.

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