Beet and Turnip Storage

Overview

Beets, turnips, and rutabagas are root vegetables requiring precise environmental control for extended storage life. Proper refrigeration system design and operation maintains marketable quality for 4-6 months under optimal conditions. The primary challenges include maintaining extremely high relative humidity to prevent moisture loss while managing respiration heat and preventing condensation-related decay. Top removal before storage is critical as continued leaf respiration accelerates deterioration and introduces disease vectors.

Storage Requirements by Crop Type

Table Beets (Beta vulgaris)

Optimal Storage Conditions:

Critical Requirements:

• Top Removal: Leaves must be removed leaving 2-3 cm stem to prevent water loss through transpiration and reduce disease entry points
• Wound Healing: 10-15°C for 4-7 days post-harvest allows suberization of cut surfaces before cold storage
• Moisture Retention: Film-lined bins or perforated polyethylene bags maintain microclimate humidity
• Disease Management: Temperature below 3°C suppresses Botrytis cinerea and bacterial soft rot pathogens

Turnips (Brassica rapa)

Optimal Storage Conditions:

Specific Considerations:

• Variety Selection: European varieties store better than Asian types
• Pithiness Development: Lower humidity (95% vs 98%) reduces internal breakdown risk
• Odor Management: Turnips produce volatile sulfur compounds; separate storage from other crops recommended
• Sprouting Control: Temperatures consistently below 2°C prevent sprouting

Rutabagas (Brassica napobrassica)

Optimal Storage Conditions:

Enhancement Practices:

• Wax Coating Application: Hot wax (60-70°C) applied post-curing reduces moisture loss by 60-80%
• Curing Before Waxing: 10-15°C, 90-95% RH for 7-10 days heals harvest wounds
• Extended Storage: Waxed rutabagas maintain quality 2-3 months longer than unwaxed

Pre-Storage Curing Requirements

Curing Protocol for Beets and Rutabagas

Curing Room Specifications:

Physiological Changes During Curing:

• Suberization: Cork layer forms over cut surfaces and abrasions
• Lignification: Cell walls strengthen at wound sites
• Wound Periderm: Protective tissue layer develops in 5-7 days
• Respiration Peak: Initial 2-3 day spike then decline as healing progresses

Curing Load Calculations:

Total cooling load during curing includes product respiration, heat of respiration, and moisture evolution.

$$Q_{total} = Q_{resp} + Q_{field} + Q_{infiltration}$$

Where:

Product Respiration Load:

$$Q_{resp} = m \times R \times H_{co2}$$

Where:

• $m$ = mass of product (kg)
• $R$ = respiration rate (mg CO₂/kg·h)
• $H_{co2}$ = heat evolved per mg CO₂ (0.0056 kJ/mg)

Example Calculation for 50,000 kg Beets at 15°C:

Respiration rate at 15°C: ~35 mg CO₂/kg·h

$$Q_{resp} = 50,000 \times 35 \times 0.0056 = 9,800 \text{ kJ/h} = 2.72 \text{ kW}$$

Field Heat Removal:

$$Q_{field} = m \times c_p \times \Delta T$$

Where:

• $c_p$ = specific heat of product (3.6 kJ/kg·K for root vegetables)
• $\Delta T$ = temperature difference (field temp - curing temp)

Assuming field temperature 25°C, curing target 15°C:

$$Q_{field} = 50,000 \times 3.6 \times 10 = 1,800,000 \text{ kJ}$$

For 24-hour pulldown:

$$Q_{field} = \frac{1,800,000}{24 \times 3600} = 20.8 \text{ kW}$$

Total Initial Curing Load: 23.5 kW minimum cooling capacity required

Cold Storage System Design

Temperature Control System

Refrigeration Equipment Specifications:

Cooling Load Calculations for Cold Storage:

Total refrigeration load during storage period:

$$Q_{storage} = Q_{resp,cold} + Q_{transmission} + Q_{infiltration} + Q_{equipment} + Q_{lights} + Q_{people}$$

Product Respiration at Storage Temperature (0°C):

For 50,000 kg beets at 0°C:

• Respiration rate: 7 mg CO₂/kg·h

$$Q_{resp,cold} = 50,000 \times 7 \times 0.0056 = 1,960 \text{ kJ/h} = 0.54 \text{ kW}$$

Transmission Load Through Insulated Walls:

$$Q_{trans} = U \times A \times \Delta T$$

For typical 500 m² storage room with U = 0.25 W/m²·K, outdoor temperature 20°C:

$$Q_{trans} = 0.25 \times 500 \times 20 = 2,500 \text{ W} = 2.5 \text{ kW}$$

Infiltration Load:

$$Q_{infil} = V \times \rho \times c_p \times \Delta T \times N$$

Where:

• $V$ = room volume (m³)
• $\rho$ = air density (1.2 kg/m³)
• $N$ = air changes per 24 hours (1-2 for well-sealed storage)

For 2,000 m³ room, 1.5 air changes/day:

$$Q_{infil} = \frac{2,000 \times 1.5 \times 1.2 \times 1.006 \times 20}{24} = 3,018 \text{ W} = 3.0 \text{ kW}$$

Equipment, Lighting, People: ~1.5 kW

Total Storage Load: 0.54 + 2.5 + 3.0 + 1.5 = 7.54 kW

Design Capacity with Safety Factor: 7.54 × 1.25 = 9.4 kW minimum

Humidity Control System

High Humidity Maintenance Strategies:

1. Evaporator Design Optimization

• Large Coil Surface Area: Reduces temperature differential, minimizes dehumidification
• Low Fin Density: 6-8 fins per inch prevents excessive moisture removal
• Oversized Coils: 50-75% larger than minimum capacity allows lower TD operation

2. Active Humidification

Humidification Load Calculation:

Mass of water required to maintain humidity:

$$\dot{m}w = \frac{V \times \rho \times N \times (W{target} - W_{supply})}{24}$$

Where:

• $W$ = humidity ratio (kg water/kg dry air)
• $N$ = air changes per day

At 0°C, 100% RH: $W_{target}$ = 0.00378 kg/kg At 0°C, 50% RH (outdoor winter): $W_{supply}$ = 0.00189 kg/kg

For 2,000 m³, 1.5 air changes/day:

$$\dot{m}_w = \frac{2,000 \times 1.2 \times 1.5 \times (0.00378 - 0.00189)}{24} = 0.227 \text{ kg/h}$$

3. Moisture Barrier Films

• Bin Liners: 4-6 mil polyethylene with perforations (2-4% open area)
• Pile Covers: Microporous films allow respiration while retaining moisture
• Bag Storage: Individual product bags maintain localized 99-100% RH microclimate

Air Circulation System Design

Airflow Requirements:

Fan Selection Criteria:

$$CFM_{required} = \frac{Q_{sensible}}{1.08 \times \Delta T}$$

For 7.0 kW sensible load at 3°C TD:

$$CFM = \frac{7.0 \times 3412}{1.08 \times 3 \times 1.8} = 4,044 \text{ CFM}$$

Convert to metric: 4,044 CFM = 1.91 m³/s

Fan Specifications:

Air Distribution Patterns:

Horizontal Flow System:

• Evaporator on one wall, return on opposite wall
• Air travels horizontally across product
• Suitable for pallet storage
• Requires 3-4 m minimum aisle width

Vertical Flow System:

• Ceiling-mounted evaporators
• Downward air distribution
• Better for bulk bin storage
• Reduces stratification risk

Perimeter Flow:

• Multiple evaporators around room perimeter
• Central return plenum
• Excellent uniformity
• Higher installation cost

Insulation and Vapor Barrier Requirements

Insulation Performance Specifications:

Material Selection:

• Polyurethane Foam Panels: Lowest thermal conductivity (0.022-0.028 W/m·K)
• Polystyrene (EPS/XPS): Cost-effective, moderate performance
• Polyisocyanurate: High R-value per inch, good moisture resistance

Vapor Barrier System:

• Interior Surface: 6-mil polyethylene, all seams sealed
• Exterior Surface: Breathable membrane allows outward moisture migration
• Penetrations: All electrical, piping sealed with expanding foam
• Doors: Dual gasket system, cam-lift hinges for compression seal

Packaging and Storage Configuration

Film Bag Storage Systems

Bag Specifications:

Permeability Requirements:

Film must balance:

• O₂ Transmission: Allow aerobic respiration (8-10 mL/m²·day minimum)
• CO₂ Transmission: Prevent accumulation above 5% (causes off-flavors)
• Water Vapor: Minimize transmission (maintain internal condensation film)

Modified Atmosphere Development:

Inside sealed bags with proper perforation:

• O₂ concentration: 10-15% (ambient 21%)
• CO₂ concentration: 3-5% (ambient 0.04%)
• Slows respiration rate by 20-30%
• Extends storage life 1-2 months

Bulk Bin Storage

Bin Design Parameters:

Air Distribution Through Bins:

Pressure drop through packed root vegetables:

$$\Delta P = K \times \rho \times v^2 \times \frac{L}{D_h}$$

Where:

• $K$ = friction factor (0.8-1.2 for roots)
• $L$ = depth of product
• $D_h$ = hydraulic diameter (equivalent void diameter)

For 1.0 m deep bins, target velocity 0.15 m/s:

• Pressure drop: 15-25 Pa
• Requires adequate fan static pressure capability

Pallet Storage Configuration

Pallet Specifications:

• Dimensions: 1200 × 1000 mm (ISO standard)
• Load Capacity: 750-1,000 kg per pallet
• Material: Plastic (cleanable) or heat-treated wood
• Configuration: 4-way entry for forklift access

Stacking Pattern:

• Height: 4-5 pallets maximum (5-6 m total)
• Aisle Width: 3.5-4.0 m for reach truck access
• Block Stacking: Not recommended (restricts airflow)
• Racked Storage: Single-deep or double-deep racking with airflow channels

Temperature Monitoring:

• Sensors at multiple heights within stack
• Core temperature monitoring in center pallets
• Wireless sensor networks for large facilities
• Data logging every 15-30 minutes

Quality Monitoring and Control

Temperature Monitoring System

Sensor Placement Strategy:

Alarm Thresholds:

• High Temperature: +1.0°C above setpoint for >30 minutes
• Low Temperature: -0.5°C below freezing point for >15 minutes
• Rate of Change: >2°C/hour indicates equipment failure
• Communication: Text/email alerts to facility manager

Humidity Monitoring

Measurement Technology:

Critical Monitoring Points:

• Supply Air: Indicates dehumidification occurring
• Return Air: Actual room condition
• Product Surface: Wireless probes in product mass
• Differential: Supply-return difference indicates moisture removal rate

Humidity Control Strategy:

IF RH < 97%:
    Activate humidification system
    Reduce evaporator TD (increase coil temperature)
    Verify door seals and infiltration

IF RH > 100% (condensation):
    Increase air velocity over product
    Check defrost scheduling
    Verify product temperature uniformity

Product Quality Assessment

Physical Inspection Schedule:

Quality Degradation Indicators:

Weight Loss:

• Acceptable: <5% over 6-month storage
• Calculation: $WL = \frac{W_0 - W_t}{W_0} \times 100$
• Correlates directly with RH control effectiveness

Firmness Loss:

• Measured with penetrometer (5-8 mm tip)
• Fresh: 50-70 N force required
• Storage limit: >30 N (maintains marketability)
• Below 20 N: Significant quality loss

Disease Incidence:

• Survey for bacterial soft rot, Botrytis, Rhizopus
• Acceptable: <2% affected at 4 months
• Above 5%: Indicates temperature or humidity excursion

Sprouting:

• Complete sprouting suppression at 0°C
• Any sprouting indicates temperature above 2°C periods

Carbon Dioxide Management

CO₂ Accumulation:

Root vegetable respiration produces CO₂ that accumulates in sealed storage:

$$CO_2\text{ production rate} = R \times \frac{44}{32}$$

Where 44/32 converts mg O₂ consumed to mg CO₂ produced.

For 50,000 kg beets at 7 mg CO₂/kg·h:

$$CO_2 = 50,000 \times 7 = 350,000 \text{ mg/h} = 0.35 \text{ kg/h}$$

Ventilation Requirements:

To maintain CO₂ below 0.5% by volume:

$$Q_{vent} = \frac{CO_2\text{ production}}{C_{max} - C_{ambient}} \times 0.509$$

Where:

• $C_{max}$ = 5,000 ppm (0.5%)
• $C_{ambient}$ = 400 ppm
• 0.509 = conversion factor

$$Q_{vent} = \frac{350}{5000 - 400} \times 0.509 = 0.039 \text{ m}^3\text{/s} = 82 \text{ CFM}$$

Ventilation System:

• Timing: Nighttime operation when outdoor temperatures low
• Control: CO₂ sensor activates ventilation above 1,500 ppm
• Air Exchange: 2-4 room volumes per 24 hours sufficient
• Heat Recovery: ERV system maintains humidity while ventilating

Waxing Systems for Rutabagas

Wax Application Process

Wax Formulation:

Application System Specifications:

Wax Tank:

• Capacity: 200-500 liters
• Temperature Control: 60-70°C ±2°C
• Material: Stainless steel with insulation
• Heating: Electric elements with thermostat

Application Methods:

1. Dip Tank System:

   • Product conveyed through wax bath
   • Immersion time: 2-5 seconds
   • Drip time: 10-15 seconds before packaging
   • Production rate: 1,000-2,000 kg/hour

2. Spray Application:

   • Atomized wax sprayed on rotating product
   • More uniform coating possible
   • Lower wax consumption (30-40% less)
   • Higher equipment cost

Coating Thickness:

Target: 50-100 micrometers

• Thinner coatings (<50 μm): Insufficient moisture barrier
• Thicker coatings (>100 μm): Waste of material, poor appearance

Quality Control:

• Visual inspection: Uniform coverage, no bare spots
• Adhesion test: Tape test after 24-hour cure
• Thickness measurement: Ultrasonic or destructive sectioning
• Weight gain: 1-2% product weight indicates proper coating

Post-Waxing Storage

Cooling Procedures:

1. Ambient Cooling: 20-22°C for 12-24 hours (wax solidification)
2. Gradual Cooling: Reduce to 10°C over 2-3 days
3. Final Storage: Transfer to 0°C cold storage

Benefits of Waxing:

• Moisture Loss Reduction: 60-80% less weight loss vs. unwaxed
• Appearance Maintenance: Glossy surface, reduced shriveling
• Extended Storage: Additional 2-3 months marketable life
• Disease Barrier: Physical barrier reduces pathogen entry

Energy Efficiency Optimization

System Efficiency Measures

Refrigeration System Optimization:

Load Management:

• Staggered Defrost: Never defrost all coils simultaneously
• Off-Peak Cooling: Use night setback for maximum refrigeration
• Thermal Mass: Pre-cool product during low-rate periods
• Heat Recovery: Use rejected condenser heat for facility heating

Monitoring and Analysis:

Calculate specific energy consumption:

$$SEC = \frac{kWh_{total}}{kg \cdot months}$$

Benchmark performance:

• Good: <0.8 kWh/kg·month
• Average: 0.8-1.2 kWh/kg·month
• Poor: >1.2 kWh/kg·month (indicates inefficiency)

Troubleshooting Common Storage Problems

Excessive Weight Loss

Causes:

• RH below 95%
• Excessive air velocity (>0.3 m/s)
• High evaporator TD (>5°C)
• Poor vapor barrier on bins/bags

Solutions:

• Install or increase humidification
• Reduce fan speed or cycle operation
• Increase coil size or reduce capacity
• Apply film liners to bins

Condensation and Surface Rot

Causes:

• Temperature cycling
• Inadequate air circulation (dead zones)
• Product temperature above room temperature
• Rapid door opening/warm infiltration

Solutions:

• Improve temperature control stability
• Reposition fans or add circulation fans
• Ensure complete product pulldown before storage
• Install air curtains or strip curtains on doors

Sprouting

Causes:

• Temperature above 2°C for extended periods
• Light exposure during storage
• Improper curing (insufficient wound healing)

Solutions:

• Verify temperature sensors accurate and well-placed
• Eliminate all light sources in storage
• Improve curing protocol before cold storage

Internal Breakdown (Pithiness)

Causes:

• Humidity too low (<90%)
• Storage temperature fluctuations
• Advanced maturity at harvest
• Variety susceptibility

Solutions:

• Increase humidity to 95-98% range
• Improve temperature stability (±0.5°C)
• Harvest at optimal maturity
• Select storage-adapted varieties

Economic Considerations

Capital Cost Estimates

Storage Facility (1,000 tonne capacity):

Waxing Line (2,000 kg/hour):

• Equipment: $150,000-250,000
• Installation: $30,000-50,000
• Wax Material: $2-3/kg product (consumable)

Operating Cost Analysis

Annual Operating Costs (1,000 tonne facility):

Return on Investment:

Extended storage allows:

• Sale during off-season premium pricing periods
• 20-40% price premium over harvest-time prices
• Breakeven storage duration: 3-4 months typically
• Maximum economic storage: 5-6 months for quality varieties

File Path: /Users/evgenygantman/Documents/github/gantmane/hvac/content/refrigeration-systems/food-processing-refrigeration/vegetable-processing/root-vegetables/beet-turnip-storage/_index.md

This comprehensive technical document provides HVAC professionals with complete specifications for designing and operating beet, turnip, and rutabaga storage facilities including refrigeration loads, humidity control, air distribution, quality monitoring, and economic analysis.