Transcript Thermal Processing - Food Science, Rutgers SEBS

Engineering and thermal
processing
Engineers are different from scientists
• What do scientists do? (Technologists?)
• What do engineers do?
• The importance of simplifying assumptions
– Examples
• How long does it take to drive to Boston?
• Large equipment
Dimensional analysis
How many inches from here to Boston?
Engineers deal with
• Heat transfer, always runs from hot to cold so
refrigerators or freezers need pumps (energy
input)
• Mass transfer
• Mass balance
– Consider a simple drier
nd
2
The
Law of Thermodynamics:
everything goes to maximum
randomness (entropy)
• Unless you put in energy
– Electric, microwave, pressure, thermal, ionizing
– Types of Heat Transfer (demo)
• Conduction
• Convection
• Radiation
Most food processing involves
the addition or removal of energy.
Most types of food spoilage have
engineering solutions.
Thermal Processing and Refrigeration
Heating and Cooling:
• Heat transfer (heating or cooling) is driven by ΔT (the
temperature difference)
ΔT (°F)
Boiling H2O
152
Oven 350°F
292
Broiler @ 2000°F
1940
Refrigerator 40°F
20
Household Freezer 10°F
50
Commercial Freezer -40°F
100
Liquid Nitrogen -380°F
440
Assume a Room
Temperature of
60°F.
Pasteurization:
• 7 log kill for Salmonella in Milk = 99.99999%
Temperature:
145°F (63C)
161°F (72C)
212°F (100C)
280°F (131C)
Time:
30 min
15 sec
0.01sec
6 sec
• Pasteurization of eggs:
3 log reduction = 99.9% 145°F for 3 to 4 mins.
• Fruit juices were just heated to reduce microbial count
and inactivate enzymes when they were thought not to
carry pathogens. Now that pathogens have been
discovered, they are pasteurized.
Log Numbers
Time (min)
1
2
3
4
5
6
7
8
9
10
# survivors
1,000,000
100,000
10,000
1,000
100
10
1
0.1
0.01
0.001
Log # survivors
6
5
4
3
2
1
0
-1
-2
-3
Log vs linear
Pasteurizers (Ohio State University)
80 C for thirty seconds
60 C for thirty minutes
Canning:
• Invented by Appert in 1790s.
• Commercial sterility.
• Destroys pathogens and spoilage organisms
that can grow.
• Requirements for high acid foods (pH < 4.6)
are not very stringent. Why?
• Can be done in a boiling water bath.
Home canned tomatoes, OK
Home canned beans, No
Requirements for low acid
(pH >4.6) foods are very strict
• Low acid foods pH > 4.6
• Target is C. botulinum 12
log reduction =
99.9999999999%
• 2 to 4 min @ 250°F
• Requires certified retort
operators, approved
process
Flow Chart: Canning of Corn (FAO)
Blanching!
Flow Chart: Canning of Peas (FAO)
Flow Chart for the pea canning process
Blanching!
Mild vs. Severe Heat Treatment:
Mild Heat Treatment):
Severe Heat Treatment:
•Aims:
•Kill pathogens
•Reduces bacterial load (Food
is not sterile)
•Inactivate enzymes
•Advantages:
•Minimal damage to flavor,
texture, and nutritional quality.
•Disadvantages:
•Short shelf life
•Another preservation method
must be used, such as
refrigeration or freezing
•Examples:
•Pasteurization
•Blanching
•Aims:
•Kills all bacteria
•Food will be commercially
sterile
•Advantages:
•Long shelf life
•No other preservation method
is necessary
•Disadvantages:
•Food is over-cooked
•Major changes in texture,
flavor, and quality
•Examples:
•Canning
Refrigeration and Freezing:
(85 % of food is frozen at some point)
Refrigeration:
Freezing:
Micro growth
Slow
Stops
Chemical reactions
Slow
Even Slower
Quality
“Fresh”
“Frozen”
Shelf life
Short
Long
Margin of error
Small (spoilage, chill injury, cross
Large
contamination)
Freezing:
Slowly:
•Water migrates
•Freeze “pure”
•Solutes concentrate
•Large crystals
Rapidly:
•Freezes in place
•No solute concentrate
•Small crystals
•Better structures
How refrigeration works
Simplified
Energy
Input
Condense
Expand
Freezing:
• 3 Types:
– Plate Freeze
• Contact with very cold surface
– Blast Freeze
• Very cold air
• Very high velocity
– Immersion
• N2
• Flash Frozen = “IQF”
Processing can create multiple
products– Apple Juice
Bottle – “hot pack”
Clear glass
Brown plastic
Concentrate
Liquid
Frozen
Metal can
Aseptic – Brix pack
(“Sipps”)
How pumpkin pies are made…