Agenda
Pasteurization
Process Control
Materials
Heat Transfer Test
Next Week
Cumulative “Final” Test
Sterile Filtration
• Alternative to pasteurization for
microbiological stabilization
• Avoid heat treatment, flavor deterioration
• Occurs before packaging (could be
contaminated after filtration, before package)
Process Requirements
• Feedstock microbiological and non-mb loads
(concentration and particle size)
• Filtrate concentration, product spoilage
concentration allowed
• Product viscosity, density, flow characteristics
Microbiological Load Reduction – LRV
Sterile Filters = 99.9999999999% LRV
No. of Organisms at Inlet
Titre Reduction 
No. of Organisms at Outlet
Filtration Mechanisms
• Direct Interception – Pore smaller than particle
• Charge Effects – Particles (-), so filter (+)
• Inertial Impactation – Particles want straight
path, fluid curves (different densities required)
• Diffusional Impactation – Random motion (gas)
Key Features Effecting Filter Performance
• Pore geometry
• Membrane thickness
• Surface Charge
Removal Ratings
• Nominal – “An arbitrary micron value assigned
by the filter manufacturer, based upon removal
of some percentage of a given size or larger.”
• Absolute – “The diameter of the largest hard
spherical particle that will pass through the
filter under a specified test condition.”
Factors effecting
flow rate and life:
• Pressure Drop
• Surface Area
P increases as dirt
blocks pores
Increased surface
area has great
increase on dirt
capacity
Surface area
can be increased
with pleats
Filter sizes:
• Pre-filter: 1.5 m
• Sterile: 0.45 m
Cleaning
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Backwash (high V)
Hot Liquor
Sodium Hydroxide
Steam Sanitized
(120C, 20 min)
Pasteurization
• Inactivate all microorganisms
• Inactivate undesired enzymes (chem. changes)
Five Key Factors for Effective Pasteurization
• Temperature
• Time
• Types of microorganisms present
• Concentration of microorganisms present
• Chemical composition of the product
Pasteurization Level
• Decimal reduction time, D – Time required to
inactivate 90% of microorganisms present
• Temperature dependence value, Z – Increase in
temp. require to increase D value by 90%
Pasteurization Units
• Measure of effect of heat and time on
microorganisms
• 1.0 PU corresponds to 1 minute at 60C
• PU = t * 1.393(T-60C) (t in minutes)
Rules of Thumb
• Increase T by 2C, double PU’s for same time
• Increase T by 10C, PU’s increase 10x
• 20 PU’s indicates that 1 in 10 Billion
microorganisms survive
Effect of PU’s on specific microorganisms needed
Plate/Flash Pasteurization
Typical plates: Stainless steel, 0.6 mm thickness
Can withstand 20 bar pressure
Design Factors for Plate Pasteurizer
• Product Flow Rate and Properties of Liquid
• Temperature Program and Pressure Drop
• Hygiene and Cleaning
Plate Pasteurizer Design
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95% Heat Recovery in regenerator
Product enters Pasteurizer at  4C
Holding temperature  72C
Holding time  25 seconds
Hot water typically used for heating, 2C
warmer than holding temperature
Level of Regeneration
Plate Pasteurizer Control
• 0.15C corresponds to 1 PU
Flow Control Options
• Fixed Flow
• Range of Pre-set Flows
• Fully Variable Flow
Most Suitable Option Depends Upon
• Size of Outlet Buffer Tank
• Importance of No Recirculation of Product
• PU Variation Desired
• Product Quality
• Type of Filler
Minimum Flow typically 1/3 of maximum
• Pressure drop 1/9 of max flow (must be
adjusted downstream to avoid overpressure)
• Heat transfer coefficient decreases, residence
time increases
Best Practice - Full flow to 1/3 of full in 15 min while
maintaining PU’s within 2.0
Control Loops
• Holding Cell Temperature
• Critical for PU Control
• Must be varied with changes in flow
• Final Product Outlet
• Flow – Upstream and downstream influences
• Pressure – Varied with changes in flow
Interrelationships of many variables requires use of
sophisticated control (PLC)
Tunnel Pasteurization
Factors Effecting Tunnel Pasteurization
• Materials of Construction
• Structure and weight – lighter stronger matl
• Corrosion – chemical attack metal, cracking
• Transport System – typically conveyor
• Spray System – Votex or spray pan
• Temperature
• Heating
• PU Control
Typical temperature regime
Plate/Flash vs. Tunnel Pasteurization
• Plate uses significantly less floor space
• 15% reduction in operating cost
• Reduced capitol costs
• Beer tastes fresher (approx 92% less TIU)
• Cleaning and contamination downstream
Why is Process Control Needed?
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Safety
Quality Specifications, Consistency
Environmental Regulation, Environmental Impact
Optimum Operation of Equipment
Cost Effectiveness
Aims of Control System
• Suppress Influence of External Disturbances
• Ensure Stability of a Process
Example: External Disturbance on Shower
• Flow rate of hot water increases?
• Temperature of hot water decreases?
• Flow rate of hot water decreases?
Stable vs. Unstable Variable
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Goal: Boil Water in an Open Pot at 1 atm
Control Variables: Amount of Water, Rate of Heat
Given Quantity of Water, Sufficient Heat = Boiling
While Boiling: Temp is Stable (or Self-Regulating)
Water Level is Un-Stable, Requires Control
Pressure Cooker Example
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No Pressure Relief – Temp and Press Unstable
With Pressure Relief – Temp and Press Stable
Level Unstable in Both
Weight = Inherent Control Scheme
Process Control – A system of measurements and
actions within a process intended to insure that the
output of the process conforms with pertinent specs
Basic Control Elements
• Sensor – Receives Stimulus, Outputs Signal
• Controller – Receives Signal, Compares to
Desired Value, Sends Control Signal
• Actuator – Receives Control Signal, Makes
Corrective Action on Process
• Process – “The Organized Method of Converting
Inputs to Outputs
Functions of Control System
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Measure
Compare to Desired Value
Compute Error
Corrective Action
Definitions
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Controlled Variable
Setpoint
Measured Variable
Manipulated Variable
Example
Disturbance?
Variables
Controlled?
Measured?
Manipulated?
More Accurate
More Complicated
On/Off Control
• Valve Open or Closed, Heater On or Off
• Inexpensive and Simple
• Oscillatory, Wear on Switching Device
Sequence Control
• Series of Events (Washing Machine)
• CIP Sequence, Fermentation Temperature, Keg
Washing and Filling
• Achieved with PLC, Pegged Drum (Mechanical)
Closed-Loop Control
Open-Loop Control
• Controlled Variable Measured Prior to
Intervention by Manipulated Variable
Definitions
• Overshoot – Ratio of maximum amount by
which response exceeds steady state to final
steady state value
• Rise Time – Time required for response to
reach final value for first time
• Response Time – Time it takes for response to
settle at its new steady state value
Control Example
Proportional Control
Proportional + Integral Control
Proportional + Integral + Derivative Control
Feedback vs. Feedforward Control
Carbon and Low Alloy Steels
• Carbon Steel – Iron alloys with 0.05 to 1% C
• Low Carbon Steel – aka mild steel
• Low Alloy Steels – alloying elements with <2%
Advantages
• Inexpensive and readily available
• Easily worked and welded
• Good tensile strength and ductility
Disadvantages
• Corrosion
• Protective coatings often required
Copper
• Pure copper traditionally used
• Brass – alloyed with zink
• Bronze – alloyed with tin
Advantages
• Soft and easily worked
• Readily available for small pipes/tubes
• Resists corrosion well
• Resistant to caustic and organic acids/salts
Disadvantages
• Strong acids and oxidizing acids attack
• Cost
Stainless Steel
• Considered stainless if chromium > 11%
• Typical values 11-30% chromium
• Cr2O3 oxidation layer gives ss it’s passivity
General Corrosion
• Covers entire surface
• “Best” kind of corrosion to have
• Measurable and predictable (design for)
Galvanic Corrosion
• Two metals in contact in same electrolyte
• Less noble, less passive, more active metal
corroded, other metal protected
Erosion and Cavitation
• Abrasive particles and/or high velocity
• Cavitation corrosion (bubbles near pumps)
Sensitisation – Inter-grainal corrosion (415-825C)
Pitting – Occurs below surface, chloride ion
Localized weak points in passive surface