Churning Process

Process Overview

Butter churning converts cream into butter through mechanical agitation that inverts the fat-water emulsion. The process transforms cream (fat droplets dispersed in water) into butter (water droplets dispersed in fat). Temperature control during churning directly affects butter yield, texture, moisture content, and production efficiency.

The churning operation generates significant heat through mechanical work while requiring precise temperature maintenance. HVAC systems must remove equipment heat loads, maintain optimal working temperatures, and control humidity to prevent condensation on cold surfaces.

Critical Temperature Parameters

Churning Temperature Range

Optimal churning temperature depends on cream fat composition and desired butter characteristics:

Temperature control precision: ±0.5°C for consistent butter quality.

The churning temperature affects fat crystal structure. Too cold: excessive butter losses in buttermilk. Too warm: extended churning time, soft butter, poor texture.

Temperature Control During Process Stages

Phase 1: Agitation and Fat Destabilization

• Duration: 15-45 minutes (batch), continuous (continuous systems)
• Temperature rise: 1-2°C from mechanical work
• Cooling requirement: Active temperature maintenance

Phase 2: Butter Grain Formation

• Critical temperature maintenance: ±0.5°C
• Heat generation: 0.8-1.2 kW per 1000 L cream capacity
• Temperature uniformity: Essential for consistent grain size

Phase 3: Buttermilk Drainage

• Buttermilk temperature: 10-15°C at discharge
• Drainage time: 2-5 minutes
• No active cooling typically required

Phase 4: Washing (Optional)

• Wash water temperature: 2-4°C below churning temperature
• Volume: 20-40% of cream volume
• Purpose: Remove residual buttermilk, lactose, proteins

Phase 5: Working and Salting

• Working temperature: 12-15°C
• Temperature rise: 2-4°C from mechanical work
• Active cooling: Required for continuous systems

Batch Churning Systems

Equipment Configuration

Traditional batch churns operate with intermittent production cycles:

Barrel Churns

• Capacity: 500-5000 L cream
• Rotation speed: 20-35 rpm
• Churning time: 30-60 minutes
• Fill ratio: 35-45% of total volume

End-Over-End Churns

• Capacity: 1000-3000 L cream
• Rotation speed: 25-40 rpm
• Churning time: 20-40 minutes
• More efficient agitation pattern

Heat Load Calculations

Mechanical work converted to heat during batch churning:

Q_mech = P × η_heat × t

Where:

• Q_mech = Heat generated (kJ)
• P = Motor power (kW)
• η_heat = Fraction converted to heat (0.85-0.95)
• t = Churning time (seconds)

Typical batch churn heat loads:

Batch Churn Cooling Methods

External Jacket Cooling

• Glycol/brine circulation through churn jacket
• Coolant temperature: 2-6°C
• Heat transfer coefficient: 250-400 W/m²·K
• Jacket surface area: 1.5-3.0 m² per 1000 L capacity

Required cooling capacity:

Q_cooling = Q_mech + Q_cream

Q_cream = m_cream × cp_cream × ΔT

Where:

• m_cream = Cream mass (kg)
• cp_cream = Specific heat (3.8-4.0 kJ/kg·K for 35-40% fat cream)
• ΔT = Temperature change (K)

Internal Cooling Coils

• Stainless steel coils submerged in cream
• Coolant: Chilled water or glycol (1-4°C)
• Surface area: 0.8-1.5 m² per 1000 L capacity
• Higher heat transfer effectiveness than external jacket

Combined Cooling Systems

• Both jacket and internal coils
• Used for large capacity churns (>3000 L)
• Faster temperature recovery between batches
• Better temperature uniformity

Batch Process Room Temperature Control

Room conditions for batch churning operations:

Continuous Churning Systems

Fritz Continuous Churn

Modern high-capacity butter production uses continuous churning systems:

Process Configuration

• Continuous cream feed
• Cylindrical churning chamber with internal beaters
• Integrated buttermilk separation
• Continuous butter discharge to working section
• Production rate: 500-5000 kg butter/hour

Temperature Control Zones

Continuous System Heat Loads

Heat generation in continuous churning is constant during operation:

Churning Section Heat Load

Q_churn = P_motor × η_heat + Q_friction

Where:

• P_motor = Churning motor power (kW)
• η_heat = Heat conversion efficiency (0.85-0.92)
• Q_friction = Bearing and seal friction heat (5-10% of motor power)

Working Section Heat Load

Q_work = P_work × η_heat

Where P_work = working section motor power (typically 30-50% of churning power)

Total continuous system heat loads:

Continuous Churn Cooling System Design

Jacket Cooling Circuit

Required coolant flow rate:

m_coolant = Q_remove / (cp_coolant × ΔT_coolant)

Where:

• Q_remove = Heat removal rate (kW)
• cp_coolant = Coolant specific heat (3.4 kJ/kg·K for 30% glycol)
• ΔT_coolant = Temperature rise through jacket (3-6°C)

Design specifications:

Refrigeration System Requirements

For continuous churning operation, dedicated refrigeration capacity:

Q_refrig = Q_churn + Q_work + Q_transmission + Q_cream_cooling

Q_transmission = U × A × ΔT

Where:

• U = Overall heat transfer coefficient (0.8-1.2 W/m²·K for insulated equipment)
• A = External surface area (m²)
• ΔT = Temperature difference to ambient (K)

Safety factor: 1.15-1.25 for capacity sizing

Buttermilk Temperature Management

Buttermilk Characteristics

Buttermilk discharged from churning contains:

• 0.4-0.7% fat (represents butter losses)
• 3.5-4.0% protein
• 4.5-5.0% lactose
• Temperature: 10-15°C at discharge

Buttermilk Heat Recovery

The sensible heat in buttermilk can be recovered:

Q_buttermilk = m_buttermilk × cp_buttermilk × (T_buttermilk - T_ref)

Where:

• m_buttermilk = Mass flow rate (kg/s)
• cp_buttermilk = 3.9 kJ/kg·K (approximates skim milk)
• T_buttermilk = Discharge temperature (°C)
• T_ref = Reference temperature, typically 4°C storage

Heat Recovery System Design

Plate heat exchanger for buttermilk-to-cream heat exchange:

• Hot side: Buttermilk at 12-15°C → cooled to 4-6°C
• Cold side: Incoming cream warmed by 3-5°C
• Heat transfer effectiveness: 0.6-0.75
• Energy savings: 15-25% of cream cooling load

Assumes 20 hours/day operation, 22 days/month.

Process Room HVAC Design

Design Conditions

Summer Design Conditions

• Outdoor: 32°C DB, 24°C WB
• Indoor: 14°C, 70% RH
• Refrigeration load: Maximum

Winter Design Conditions

• Outdoor: -10°C
• Indoor: 14°C, 65% RH
• Heating load: Minimal due to equipment heat

Cooling Load Components

1. Equipment Heat Gain

Sum of all churning and working equipment as calculated above.

2. Transmission Load

Q_transmission = U_wall × A_wall × (T_outdoor - T_indoor) + U_roof × A_roof × (T_outdoor - T_indoor + ΔT_solar)

Where:

• U_wall = 0.25-0.35 W/m²·K (insulated wall)
• U_roof = 0.20-0.28 W/m²·K (insulated roof)
• ΔT_solar = 10-15°C (solar load on roof)

3. Infiltration Load

Q_infiltration = n × V × ρ_air × (h_outdoor - h_indoor)

Where:

• n = Air change rate from infiltration (0.5-1.0 ACH)
• V = Room volume (m³)
• ρ_air = Air density (1.2 kg/m³)
• h = Enthalpy from psychrometric chart (kJ/kg)

4. Lighting Load

Q_lighting = W_lighting × A_floor × f_use

Where:

• W_lighting = 8-12 W/m² (LED lighting)
• A_floor = Floor area (m²)
• f_use = Usage factor (0.8-1.0)

5. Occupancy Load

Q_occupancy = n_people × (Q_sensible + Q_latent)

Where:

• n_people = Number of operators
• Q_sensible = 75 W/person (light work at 14°C)
• Q_latent = 55 W/person

6. Product Load

Negligible for churning, as cream enters near room temperature.

Total Cooling Load Summary

For a typical continuous butter production facility (2000 kg/h capacity):

Design capacity with safety factor (1.15): 91 kW

HVAC System Configuration

Recommended System: Ducted Direct Expansion with Reheat

Air Handling Unit Specifications

• Supply air volume: 8000-12000 m³/h (15-20 ACH)
• Supply air temperature: 8-10°C
• Return air temperature: 14-15°C
• Mixed air: 70% return, 30% outdoor (minimum ventilation)
• Cooling coil: DX evaporator, 3-5°C evaporating temperature
• Reheat coil: Hot gas or electric, for humidity control
• Supply air filter: MERV 8 (minimum), MERV 11 (recommended)

Refrigeration System

• Type: Direct expansion or glycol loop from central plant
• Refrigerant: R-404A, R-507A, or R-448A (HFO alternatives)
• Evaporating temperature: 0 to -5°C
• Condensing temperature: 35-45°C (air-cooled), 30-38°C (water-cooled)
• Compressor type: Screw or scroll for continuous operation

Humidity Control Strategy

Churning rooms require dehumidification to prevent condensation on cold equipment surfaces.

Moisture removal rate:

m_moisture = ρ_air × Q_air × (ω_outdoor - ω_indoor)

Where:

• ρ_air = 1.2 kg/m³
• Q_air = Outdoor air volume flow (m³/s)
• ω = Humidity ratio from psychrometric chart (kg moisture/kg dry air)

Cooling coil dehumidification:

• Coil surface temperature: 2-4°C (below dew point)
• Condensate removal: 2-5 L/h per 1000 m³/h outdoor air
• Reheat requirement: 1.5-3 kW per 1000 m³/h to reach supply temperature

Air Distribution Design

Supply Air Delivery

• High sidewall diffusers or perforated duct
• Throw distance: 10-15 m
• Discharge velocity: 3-5 m/s
• Terminal velocity at work zone: <0.3 m/s
• Temperature differential: 4-6°C below room

Return Air Collection

• Low sidewall or floor-level returns
• Location: Away from supply air to ensure circulation
• Return velocity: <2.5 m/s at grilles
• Return air path: Minimum 3 m from supply discharge

Ventilation Air Requirements

Minimum outdoor air for odor control and pressurization:

• 0.5 L/s per m² floor area (minimum)
• Or 20-30% of supply air volume
• Positive pressure: 5-10 Pa relative to adjacent spaces

Equipment Specifications

Batch Churn Cooling Requirements

Small Batch Churn (1000-2000 L)

• Jacket cooling capacity: 8-12 kW
• Coolant flow rate: 15-25 L/min
• Coolant temperature: 2-4°C
• Control valve: Modulating, 0-10 VDC signal
• Temperature sensor: RTD, ±0.2°C accuracy

Large Batch Churn (3000-5000 L)

• Jacket cooling capacity: 18-28 kW
• Internal coil capacity: 10-15 kW (if used)
• Total coolant flow: 40-70 L/min
• Coolant temperature: 2-4°C
• Control: Cascade control, inner loop on coolant valve, outer loop on cream temperature

Continuous Churn Cooling Requirements

Medium Capacity (1000-2000 kg/h butter)

• Churning section cooling: 25-35 kW
• Working section cooling: 15-20 kW
• Total coolant flow: 60-90 L/min
• Coolant supply temperature: 2-5°C
• Coolant return temperature: 6-10°C
• Temperature control: PID with feedforward compensation

High Capacity (3000-5000 kg/h butter)

• Churning section cooling: 50-75 kW
• Working section cooling: 30-45 kW
• Total coolant flow: 140-200 L/min
• Multiple cooling zones with independent control
• Redundant cooling circuits for production continuity

Refrigeration Plant Sizing

Total refrigeration capacity for churning facility:

Q_refrig_total = Q_equipment + Q_room + Q_buttermilk_cooling + Q_misc

Equipment refrigeration:

• Churn jacket/coil cooling
• Temperature: -2 to +5°C glycol supply
• Immediate response required

Room HVAC refrigeration:

• Air conditioning system
• Temperature: 0 to -5°C evaporating
• Continuous operation

Buttermilk cooling refrigeration:

• Storage tank cooling
• Temperature: 0 to +2°C glycol supply
• Scheduled operation

Design approach: Separate refrigeration circuits for equipment cooling and space conditioning to allow independent control and maintenance.

Energy Efficiency Considerations

Heat Recovery Opportunities

1. Buttermilk Heat Recovery

• Preheat incoming cream
• Energy recovery: 15-25% of cream cooling load
• Payback period: 1-2 years

2. Compressor Heat Recovery

• Hot gas desuperheater for hot water generation
• Water heating to 50-60°C for CIP systems
• Energy recovery: 20-30% of compressor power
• Payback period: 2-3 years

3. Exhaust Air Heat Recovery

• Run-around glycol loop or heat pipe
• Preheat ventilation air in winter
• Energy recovery effectiveness: 50-65%
• Payback period: 3-5 years (climate dependent)

Variable Speed Drive Applications

Refrigeration Compressors

• Load variation: 40-100% during batch operation, 70-100% continuous
• Energy savings: 15-25% compared to stepped control
• Required turndown: 3:1 minimum

Air Handling Unit Fans

• Variable air volume for load-following
• Night setback capability
• Energy savings: 20-35% compared to constant volume

Coolant Circulation Pumps

• Flow modulation based on temperature control demand
• Energy savings: 10-20% compared to constant flow

Operational Energy Optimization

Temperature Setpoint Optimization

• Churning at upper end of acceptable range (12-13°C vs 8-10°C)
• Reduces refrigeration load by 20-30%
• Must balance against butter quality requirements

Batch Schedule Optimization

• Align peak churning loads with off-peak electricity rates
• Cold storage of cream to allow flexible scheduling
• Potential cost savings: 15-30% in time-of-use markets

Load Shedding Strategies

• Pre-cool equipment during off-peak hours
• Thermal mass utilization
• Demand response participation

Control System Design

Temperature Control Architecture

Batch Churn Control

• PID control on cream temperature
• Manipulated variable: Coolant valve position
• Setpoint: 10-13°C (product dependent)
• Control precision: ±0.5°C
• Tuning: Conservative (minimize overshoot)

Continuous Churn Control

• Multi-zone cascade control
• Inner loop: Coolant temperature (fast response)
• Outer loop: Product temperature (slow response)
• Feedforward: Cream flow rate and temperature
• Control precision: ±0.3°C

HVAC Control Integration

Room Temperature Control

• Modulating cooling via refrigerant flow or coolant valve
• Reheat for humidity control
• Setpoint: 14°C ±1°C
• Night setback: 16-18°C (unoccupied periods)

Humidity Control

• Target: 65-70% RH
• Method: Overcool and reheat
• Dehumidification active when RH > 72%
• Humidification not typically required

Ventilation Control

• CO2-based demand control ventilation (if occupancy varies)
• Minimum outdoor air damper position: 30%
• Maximum outdoor air: 100% (free cooling when available)

Maintenance Requirements

Cooling System Maintenance

Weekly Tasks

• Inspect coolant levels and pressures
• Check for leaks at connections
• Verify temperature control performance
• Clean coolant strainers

Monthly Tasks

• Test coolant concentration (if glycol)
• Inspect coolant pump operation
• Check control valve operation
• Review temperature trend data

Quarterly Tasks

• Clean cooling coils and jackets
• Inspect insulation condition
• Verify control sensor calibration
• Analyze coolant for contamination

Annual Tasks

• Complete cooling system CIP (clean-in-place)
• Replace coolant (if required)
• Recalibrate all temperature sensors
• Test emergency shutdown systems

HVAC System Maintenance

Monthly Tasks

• Replace/clean air filters
• Inspect refrigerant levels and pressures
• Check condensate drainage
• Verify control sequences

Quarterly Tasks

• Clean evaporator and condenser coils
• Inspect fan belts and bearings
• Test humidity control operation
• Review energy consumption trends

Annual Tasks

• Complete refrigeration system service
• Duct cleaning and inspection
• Control system calibration
• Airflow measurements and balancing

Safety Considerations

Temperature Safety

High Temperature Alarm

• Setpoint: 16°C (churning process)
• Action: Alert operator, reduce production rate
• Consequence of failure: Soft butter, quality issues

Low Temperature Alarm

• Setpoint: 7°C (churning process)
• Action: Alert operator, reduce cooling
• Consequence of failure: Extended churning time, butter losses

Refrigerant Safety

Refrigerant Detection

• Sensors in equipment rooms and occupied spaces
• Alarm level: 25% of TLV-TWA
• Emergency ventilation activation: 50% of TLV-TWA

Emergency Procedures

• Refrigerant leak response plan
• Evacuation thresholds
• Emergency ventilation capacity: 0.3 m³/s per kg refrigerant charge

Personnel Safety

Cold Surface Protection

• Guard rails around cold equipment
• Warning signage on sub-ambient surfaces
• Personal protective equipment requirements

Electrical Safety

• Equipment in wet areas: IP67 minimum
• GFCI protection for 120V circuits
• Lockout/tagout procedures for maintenance

Related Topics:

• Cream Aging and Cooling
• Butter Working and Texturization
• CIP Systems for Churning Equipment
• Refrigerant System Design for Dairy Processing