Citrus Processing

Citrus processing refrigeration encompasses the thermal management systems required for juice extraction, concentration, storage, and preservation of oranges, grapefruits, lemons, limes, and tangerines. These systems maintain product quality, prevent enzymatic degradation, and preserve volatile flavor compounds throughout processing stages.

Processing Stage Refrigeration Requirements

Citrus processing involves multiple thermal operations, each requiring specific refrigeration conditions to maintain quality and processing efficiency.

Fresh Fruit Receiving and Storage

Raw citrus fruit storage before processing requires controlled cooling to reduce respiration rates and extend holding periods without quality deterioration.

Storage Conditions by Citrus Type:

Temperature uniformity within ±1°F across storage rooms prevents localized chilling injury and maintains consistent fruit quality for processing. Air velocity at fruit surfaces should remain below 100 fpm to minimize moisture loss while providing adequate heat removal.

Juice Extraction Cooling

Fresh-squeezed citrus juice exits extraction equipment at temperatures between 65-75°F depending on ambient conditions and mechanical heat generation. Immediate cooling arrests enzymatic activity and microbial growth.

Extraction Stage Thermal Loads:

• Mechanical heat from extraction: 15-25 BTU/gal juice produced
• Fruit sensible heat removal: 40-60 BTU/gal
• Respiration heat from peel waste: 5-10 BTU/lb peel
• Equipment motor heat rejection: 2,545 BTU/hr per motor HP

Primary cooling occurs in plate heat exchangers that reduce juice temperature from 70°F to 38-42°F within 2-3 minutes of extraction. This rapid cooling prevents cloud loss, vitamin degradation, and off-flavor development.

Chilled water or glycol loops operating at 32-35°F provide cooling medium, with approach temperatures of 3-5°F achievable in properly designed plate exchangers. Heat transfer coefficients range from 400-600 BTU/hr-ft²-°F for citrus juice at turbulent flow conditions (Re > 4,000).

Concentration Process Refrigeration

Citrus juice concentration removes water to produce frozen concentrate or single-strength bases for reconstitution. Evaporative concentration under vacuum requires substantial refrigeration for condenser operation and product cooling.

Vacuum Evaporator Condensers

Multi-effect evaporators operate at progressively lower pressures and temperatures across effects, with the final effect requiring refrigeration for vapor condensation.

Typical Evaporator Operating Conditions:

The final effect condenser typically operates with ammonia refrigeration at 35-40°F evaporating temperature, providing sufficient temperature differential for vapor condensation at vacuum conditions. Surface condensers require 1.2-1.5 ft² per lb/hr water vapor removed.

Essence Recovery Chilling

Volatile flavor compounds stripped from juice during the first evaporator pass require immediate condensation and cooling to preserve aromatic quality.

Essence recovery condensers operate at 32-38°F to condense water vapor carrying flavor oils, aldehydes, and esters. Two-stage condensation provides optimal recovery:

1. Primary condenser at 38°F removes bulk water and heavy aromatics
2. Secondary condenser at 32°F captures light volatile compounds

Refrigeration load for essence recovery ranges from 80-120 BTU/gal single-strength juice processed, with peak loads occurring during high-volume production periods.

Frozen Concentrate Production

Production of frozen concentrated orange juice (FCOJ) and other citrus concentrates requires precise thermal control to achieve target soluble solids while maintaining quality.

Concentrate Cooling and Freezing

Concentrated juice exits the evaporator at temperatures between 75-85°F and must be rapidly cooled to prevent non-enzymatic browning and flavor degradation.

Concentrate Cooling Stages:

Scraped surface heat exchangers maintain product movement during freezing to prevent ice crystal formation and maintain smooth texture. Evaporating refrigerant at 0 to -10°F provides driving force for rapid heat extraction.

Cutback and Blending Operations

Concentrated juice at 58-65° Brix receives additions of fresh juice (cutback), cold-pressed oil, and pulp to restore fresh-like flavor characteristics. These operations occur at 35-40°F to maintain product stability.

Refrigerated blending tanks maintain 38°F with chilled glycol jackets, removing heat generated by agitation (10-15 BTU/hr per HP of agitator power) and preventing quality loss during batch preparation.

Cold Storage Systems

Citrus products require different storage conditions based on concentration level and intended use.

Single-Strength Juice Storage

Pasteurized not-from-concentrate (NFC) juice storage occurs at 28-32°F to maximize shelf life while preventing freeze damage. Storage duration extends 4-8 weeks under these conditions.

Refrigeration systems maintain temperature uniformity within ±0.5°F through high air circulation rates (60-80 air changes per hour) and multi-point temperature sensing with averaging control.

Specific storage requirements:

• Air velocity: 200-300 fpm across storage tank surfaces
• Insulation: R-30 minimum for walls, R-40 for ceilings
• Temperature control: ±0.5°F of setpoint
• Defrost cycles: Every 6-8 hours for 20-30 minutes

Frozen Concentrate Storage

FCOJ storage at -10 to 0°F maintains product quality for 18-24 months. Storage facilities utilize low-temperature refrigeration systems with provisions for product hardening and quality preservation.

Frozen Storage Design Criteria:

Quality Preservation Through Refrigeration

Specific refrigeration strategies prevent quality degradation mechanisms in citrus products.

Vitamin C Retention

Ascorbic acid (vitamin C) degradation follows first-order kinetics, with reaction rate doubling approximately every 18°F temperature increase. Storage at 32°F versus 50°F results in 3-4 times longer vitamin retention.

Refrigeration systems maintaining ±1°F control provide predictable vitamin retention:

• At 32°F: 90% retention after 8 weeks
• At 40°F: 90% retention after 4 weeks
• At 50°F: 90% retention after 2 weeks

Cloud Stability Maintenance

Citrus juice cloud (suspended pulp particles) remains stable at temperatures below 45°F. Warm storage or thermal cycling causes pectinesterase enzyme activation and cloud loss.

Refrigeration systems prevent cloud loss through:

1. Rapid post-extraction cooling to <42°F within 3 minutes
2. Continuous storage at 32-38°F without temperature cycling
3. Distribution cold chain maintenance at <40°F throughout

Color Preservation

Non-enzymatic browning reactions proceed at reduced rates under refrigeration. Color degradation (ΔE colorimetric units) accumulates at temperature-dependent rates:

• At 32°F: 0.5 ΔE units per month
• At 50°F: 2.0 ΔE units per month
• At 70°F: 8.0 ΔE units per month

Refrigerated storage below 40°F maintains acceptable color for the product’s intended shelf life.

Refrigeration System Design Considerations

Citrus processing facilities require integrated refrigeration systems serving multiple temperature levels and processing operations.

Multi-Temperature Systems

Centralized ammonia refrigeration systems typically serve three temperature zones:

1. High-temperature (45-50°F): Fresh fruit storage, extract cooling
2. Medium-temperature (28-35°F): Juice storage, process cooling
3. Low-temperature (-10 to 0°F): Frozen concentrate storage

Suction grouping and evaporator temperature control through back-pressure regulation provides efficient operation across temperature ranges.

Seasonal Load Variation

Citrus processing exhibits extreme seasonal variation, with Florida orange processing concentrated in November through June and California operations extending year-round.

Peak processing loads occur during harvest peaks (December-February for Florida), requiring refrigeration capacity 2-3 times average annual load. System design must accommodate:

• Peak day capacity: 150-200% of average capacity
• Shoulder season operation: 40-60% of peak capacity
• Off-season maintenance and cleaning periods

Variable-speed compressors and staged capacity control provide efficient operation across this wide load range.

Heat Recovery Opportunities

Citrus processing facilities generate substantial heat rejection from refrigeration condensers, evaporators, and pasteurization operations. Heat recovery applications include:

• Hot water generation for equipment cleaning (140-180°F)
• Evaporator feed preheating (reducing steam consumption 15-25%)
• Building heating during winter processing
• Ambient air heating for concentrate spray drying operations

Refrigeration system design incorporating heat recovery can reduce facility energy consumption by 20-30% compared to rejection-only configurations.

Evaporator Selection for Citrus Applications

Citrus products exhibit specific characteristics requiring appropriate evaporator selection for different applications.

Process Cooling Evaporators

Plate heat exchangers provide primary cooling duty, with refrigerant-side evaporation at 32-38°F. Design considerations include:

• Minimum approach temperature: 3-5°F
• Citrus juice velocity: 4-6 ft/sec (turbulent flow)
• Fouling factor: 0.001-0.002 hr-ft²-°F/BTU
• Inspection and cleaning access every 4-8 hours

Storage Room Evaporators

Unit coolers for citrus cold storage incorporate features addressing high humidity requirements and acid-resistant construction:

• Fin spacing: 4-6 fins per inch (prevents frosting, facilitates drainage)
• Coil coating: Phenolic or epoxy for acid resistance
• Drain pan heating: Prevents freeze-up from defrost condensate
• Fan motors: Totally enclosed for wash-down environments

Air-side face velocity should remain below 500 fpm to minimize product moisture loss while achieving required refrigeration capacity.

Blast Freezing Equipment

Blast freezers for frozen concentrate hardening utilize:

• Air temperature: -20 to -30°F
• Air velocity: 1,000-2,000 fpm across product
• Freezing time: 2-4 hours from 35°F to 0°F
• Specific refrigeration load: 140-160 BTU/lb product

Horizontal airflow blast tunnels provide uniform freezing for cartoned concentrate, with product conveyed through the freezing zone on continuous belts or batch racks.

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