Cherry Handling
Overview
Cherry handling facilities require precise environmental control to maintain fruit quality from harvest through packing and storage. Cherries are highly perishable stone fruits with rapid respiration rates and susceptibility to moisture loss, stem browning, and mechanical damage. HVAC systems must provide rapid cooling capacity, tight humidity control, and conditioned packing environments to preserve stem retention, minimize decay, and extend storage life.
Sweet cherries (Prunus avium) and tart cherries (Prunus cerasus) have different handling requirements based on their market destination. Sweet cherries destined for fresh consumption require immediate cooling and controlled atmosphere storage, while tart cherries are primarily processed into frozen or canned products with less stringent environmental requirements.
Cooling Requirements
Hydrocooling Systems
Hydrocooling is the preferred cooling method for cherries due to its rapid heat removal rate and ability to minimize moisture loss. The high thermal conductivity of water enables cooling rates 15-20 times faster than air cooling.
System design parameters:
- Water temperature: 0 to 2°C (32 to 36°F)
- Contact time: 3 to 5 minutes
- Water velocity: 0.3 to 0.5 m/s (60 to 100 ft/min)
- Target pulp temperature: 2 to 4°C (36 to 39°F)
- Refrigeration capacity: 120 to 150 kW per tonne/hour (410 to 510 MBH)
Hydrocooling systems use either immersion tanks or flume-type conveyors. Immersion systems provide better temperature uniformity but require careful handling to prevent fruit damage. Flume systems integrate with packing line conveyors but require higher water flow rates.
Water treatment requirements:
- Chlorination: 100 to 150 ppm free chlorine
- pH control: 6.5 to 7.5
- Filtration: 50 micron or finer
- Water temperature monitoring: ±0.5°C accuracy
- Replacement rate: 10 to 15% per hour
The refrigeration system must maintain water temperature despite the continuous heat load from incoming fruit. Typical cherry harvest temperatures range from 15 to 25°C (59 to 77°F), requiring removal of 55 to 85 kJ/kg (24 to 37 BTU/lb) of field heat.
Forced-Air Cooling
Forced-air cooling provides an alternative to hydrocooling for facilities without water treatment capability or when stem wetness must be minimized. The cooling rate is significantly slower than hydrocooling but avoids water contact and associated decay concerns.
Design criteria:
- Air temperature: -1 to 0°C (30 to 32°F)
- Air velocity through containers: 1.5 to 2.5 m/s (300 to 500 ft/min)
- Relative humidity: 90 to 95%
- Cooling time to 7/8 cooling: 2 to 3 hours
- Airflow rate: 1.5 to 2.0 L/s per kg (1.5 to 2.0 CFM/lb)
Forced-air cooling tunnels use horizontal or vertical airflow through stacked containers. Container vent area must be at least 5% of the side wall area facing the airflow direction. The pressure differential across the load drives air through containers rather than around them.
Temperature reduction rates:
| Cooling Method | Time to 5°C | Heat Removal Rate |
|---|---|---|
| Hydrocooling | 3-5 min | 12-15 kW/tonne |
| Forced-air cooling | 2-3 hours | 1.5-2.0 kW/tonne |
| Room cooling | 12-24 hours | 0.3-0.5 kW/tonne |
Storage Requirements
Sweet Cherry Storage
Sweet cherries require cold storage immediately after cooling to maintain quality. The storage environment must balance low temperature for respiration control with humidity maintenance for stem retention.
| Parameter | Requirement | Notes |
|---|---|---|
| Temperature | 0 to 0.5°C (32 to 33°F) | ±0.5°C tolerance |
| Relative humidity | 90 to 95% | Critical for stem quality |
| Air velocity | 0.05 to 0.1 m/s (10 to 20 ft/min) | Minimize moisture loss |
| Storage life | 14 to 21 days | Variety dependent |
| Respiration at 0°C | 4 to 6 mg CO₂/kg·h | Moderate rate |
| Freezing point | -1.7 to -2.2°C (29 to 28°F) | Cultivar variation |
Refrigeration system design:
- Evaporator coil TD: 2 to 3°C (4 to 6°F) maximum
- Defrost cycle: Every 8 to 12 hours
- Defrost method: Electric or hot gas
- Multiple evaporators for capacity control
- Variable speed fans for airflow modulation
The narrow temperature differential between storage temperature and freezing point requires precise refrigeration control. Direct expansion systems with multiple circuits or flooded evaporators provide better temperature uniformity than single-circuit systems.
Tart Cherry Handling
Tart cherries are rarely stored fresh due to their processing destination. Most facilities cool tart cherries to 4 to 7°C (39 to 45°F) before immediate processing or freezing.
| Parameter | Fresh Holding | Frozen Storage |
|---|---|---|
| Temperature | 4 to 7°C (39 to 45°F) | -18 to -23°C (0 to -10°F) |
| Relative humidity | 85 to 90% | Not critical |
| Maximum holding time | 2 to 3 days | 12 to 18 months |
| Cooling rate requirement | Moderate | Rapid freeze preferred |
Humidity Control
Stem Browning Prevention
Stem browning is the primary quality defect in stored sweet cherries. The stem desiccates faster than the fruit due to its higher surface-to-volume ratio and lack of protective cuticle.
Moisture loss rates:
- Stem moisture loss: 2 to 3% per day at 85% RH
- Stem moisture loss: 0.5 to 1% per day at 95% RH
- Acceptable browning threshold: <10% stem area
Humidity control systems must maintain 90 to 95% RH without condensation on fruit surfaces. Condensation promotes decay development, particularly by Botrytis cinerea and Alternaria alternata.
Humidity generation methods:
- High-efficiency evaporators: Large coil surface area with minimal TD
- Fogging systems: Ultrasonic or high-pressure nozzles (contraindicated due to surface wetness)
- Wetted pad humidifiers: Lower disease risk than fogging
- Evaporative coolers: Limited to dry climate facilities
The preferred approach uses oversized evaporator coils with variable capacity control to minimize dehumidification while maintaining temperature. Coil face velocity should not exceed 2 m/s (400 ft/min) to reduce moisture removal.
Moisture Loss Control
Cherry moisture loss directly impacts saleable weight and appearance. Shriveling becomes visible at 3 to 5% weight loss.
| Storage Duration | Weight Loss at 90% RH | Weight Loss at 95% RH |
|---|---|---|
| 7 days | 2.5-3.5% | 1.0-1.5% |
| 14 days | 4.5-6.0% | 2.0-3.0% |
| 21 days | 6.5-8.5% | 3.0-4.5% |
Packaging in perforated polyethylene liners reduces moisture loss by 40 to 60% compared to unlined containers. The liner creates a modified humidity environment while allowing sufficient gas exchange for respiration.
Packing Line Environmental Control
Temperature Control
Cherry packing lines require cooled environments to minimize fruit temperature increase during sorting, sizing, and packing operations. Ambient temperatures above 15°C (59°F) cause measurable quality loss during the 20 to 40 minute packing process.
Packing room design criteria:
- Air temperature: 10 to 15°C (50 to 59°F)
- Relative humidity: 70 to 80%
- Air changes: 15 to 20 per hour
- Lighting: 500 to 750 lux for sorting
- Worker comfort: Balance with product cooling
The cooling load includes product heat gain, equipment heat, lighting, and worker metabolic heat. A typical packing line handling 2 tonnes/hour generates approximately 25 to 35 kW (85 to 120 MBH) of cooling load.
Load components:
| Source | Load (kW per tonne/hour) |
|---|---|
| Product warming | 4-6 |
| Equipment motors | 3-5 |
| Lighting | 2-3 |
| Workers (10 persons) | 1-2 |
| Infiltration | 3-5 |
| Total | 13-21 |
Air Distribution
Air distribution systems must provide uniform temperature throughout the packing area without creating drafts that cause worker discomfort or excessive fruit moisture loss.
Design parameters:
- Supply air temperature: 8 to 12°C (46 to 54°F)
- Supply air velocity at worker level: <0.25 m/s (50 ft/min)
- Overhead diffusers with adjustable throw
- Return air grilles at high level
- Positive pressure relative to outdoor and storage areas
Displacement ventilation systems work well in packing areas with high ceilings, supplying cool air at low velocity near floor level and allowing warm air to rise to ceiling-level returns.
Modified Atmosphere Storage
Modified atmosphere (MA) extends cherry storage life by reducing respiration and decay development. The atmosphere composition is achieved through product respiration in sealed containers or controlled generation.
Recommended atmosphere composition:
| Parameter | Sweet Cherry | Tart Cherry (if stored) |
|---|---|---|
| O₂ concentration | 3 to 10% | 5 to 12% |
| CO₂ concentration | 10 to 15% | 8 to 12% |
| Temperature | 0 to 0.5°C | 2 to 4°C |
| Maximum storage | 21 to 28 days | Not typically used |
High CO₂ atmospheres suppress fungal decay but can cause stem browning at concentrations above 20%. Very low O₂ levels (<2%) induce fermentation and off-flavor development.
System requirements:
- Gas-tight storage rooms or containers
- CO₂ scrubbing or venting capability
- O₂ and CO₂ monitoring equipment
- Atmosphere adjustment controls
- Emergency ventilation systems
Decay Control Systems
Cherries are susceptible to multiple decay organisms that develop during storage. The HVAC system plays a critical role in decay prevention through temperature and humidity control.
Primary decay organisms:
- Botrytis cinerea (gray mold): Optimal at 15-20°C, suppressed below 2°C
- Alternaria alternata (black rot): Active above 5°C
- Rhizopus stolonifer (soft rot): Requires surface moisture
- Monilinia spp. (brown rot): Significant in stone fruits
Temperature control is the primary defense against decay. Each 5°C reduction in temperature approximately doubles storage life by reducing microbial growth and respiration.
Some facilities use sulfur dioxide (SO₂) fumigation at 0.1 to 0.5% concentration for 20 to 30 minutes. This requires exhaust systems capable of purging SO₂ residues before worker entry and compliance with occupational exposure limits (2 ppm TWA, 5 ppm STEL).
Design Load Calculations
Refrigeration Load Components
Total refrigeration load for cherry storage includes multiple simultaneous heat sources:
Product load:
Q_product = m × c_p × ΔT + m × R × t
Where:
- m = product mass flow rate (kg/h)
- c_p = specific heat = 3.6 kJ/kg·°C (0.86 BTU/lb·°F)
- ΔT = temperature reduction (°C)
- R = respiration heat = 0.015 to 0.020 kW/tonne at 0°C
- t = storage time (hours)
Transmission load:
Q_transmission = U × A × ΔT
Insulation should provide U ≤ 0.25 W/m²·°C (R-23 or better) for storage rooms.
Infiltration load:
Q_infiltration = V × ρ × c_p × ΔT × N
With N = 0.5 to 1.0 air changes per day for well-sealed rooms.
Total design capacity:
Add 20 to 30% safety factor to calculated loads to account for peak conditions, future expansion, and degraded performance over equipment life.
Energy Efficiency Measures
Cherry handling facilities operate seasonally with high peak loads during harvest. Energy efficiency measures reduce operating costs during this critical period.
Efficiency strategies:
- Variable speed compressors: Match capacity to load variations
- Floating head pressure control: Reduce compression ratio during cool weather
- Heat recovery: Use rejected heat for warm water generation
- Economizer cooling: Use ambient air when outdoor temperature permits
- LED lighting: Reduce cooling load from lighting heat
- Automated controls: Optimize defrost cycles and setpoints
Well-designed facilities achieve energy efficiency ratios of 2.5 to 3.5 (8.5 to 12 EER) for refrigeration systems operating at 0°C storage temperature.
ASHRAE References
Design of cherry handling HVAC systems should reference:
- ASHRAE Handbook—Refrigeration: Chapter 37 “Deciduous Tree and Vine Fruits”
- ASHRAE Handbook—HVAC Applications: Chapter 29 “Food and Beverage Processing and Cooling”
- ASHRAE Standard 15: Safety Standard for Refrigeration Systems
- ASHRAE Standard 34: Designation and Safety Classification of Refrigerants
Specific data on cherry storage includes respiration rates, storage life as a function of temperature, recommended storage conditions, and physiological disorders.
Fruit Quality Indicators
HVAC system performance directly affects measurable quality parameters:
| Quality Factor | Measurement | Target Range |
|---|---|---|
| Stem condition | Visual rating (1-5 scale) | ≥4 (green, pliable) |
| Fruit firmness | Penetrometer (N) | 2.5-4.0 N |
| Weight loss | Gravimetric (%) | <3% after 14 days |
| Decay incidence | Visual (% affected fruit) | <5% after 21 days |
| Pitting damage | Visual (% surface area) | <2% |
| Stem pull force | Tensile tester (N) | >2.0 N |
Regular monitoring of these parameters validates HVAC system performance and identifies required adjustments before significant quality loss occurs.
Operational Considerations
Pre-cooling procedures:
- Cool storage rooms to setpoint before fruit arrival
- Verify humidity systems operational
- Check air distribution uniformity
- Calibrate temperature sensors (±0.5°C accuracy)
Loading procedures:
- Stack containers for maximum airflow
- Maintain 10 cm clearance from walls
- Align containers for vertical airflow
- Limit load height to maintain air circulation
- Monitor product temperature during loading
Monitoring requirements:
- Continuous temperature recording in multiple locations
- Humidity logging at 15-minute intervals
- Daily inspection of stem condition
- Weekly fruit temperature measurements
- Refrigeration system performance trending
Proper HVAC system design and operation maintains cherry quality from harvest through distribution, maximizing marketable yield and grower returns while minimizing energy consumption and operational costs.