Thermal Processing Quality Optimization Flashcards
What type of heat transfer occurs between the medium and the can?
Convection
What are the benefits of improved heat transfer rate?
- Faster turnover (shorter process time)
- heating uniformity
- Less overcooking
- Better quality
To optimize quality of the product, we need to (increase/decrease) processing time by improving ____.
Decrease
Heat transfer
What is the formula for convection heating?
q = hAΔT
Where does heat transfer occur between during processing? (2)
medium -> can
within can contents
What is the formula for conduction heating?
q = (kAΔT)/x
List spores, nutrients, and bacteria in order of increasing D value.
bacteria, spores, nutrients
The driving force of improving quality retention is:
improving RATE OF HEAT TRANSFER
True/False: nutrients have a higher D value but a lower z value than bacteria
False: higher D, and ALSO HIGHER Z
List 3 types of heat exchangers:
Scraped surface
Tubular
Plate and Frame
Why would short time, high temperature processing be better than longer lower temperatures at retaining nutrient quality?
Nutrients have higher D value (more resistant) and also higher Z value (D is less sensitive to temperature change)
Raising temperature will cause more decrease in D value of bacteria/spores than nutrients
The flow of product and medium in plate exchangers is usually ____.
Countercurrent
Describe each heat exchange system:
scraped surface: bottom is swept/scraped during heat process to prevent viscous fluids from burning on bottom
Tubular: product passed through tubes to be heated by medium, more surface area. higher pressure than plates
Plate and Frame: metal plates used to spread out 2 fluids, increases heat transfer rate
What systems work well with quality optimization? (2)
- In container sterilization
- Continuous Processing system (work very well)
In tube heat exchangers, the flow is _____
either countercurrent or cross current
What process parameters are very compatible with HTST or UHT?
- liquids (or liquids with small particles)
- thin packages
- processes with agitation
- continuous (aseptic)
Why would a flat product be faster in conductive heating? (2)
increased surface area (A) decreased thickness (x)
What is HTST NOT suitable for? Why?
conduction heating, especially large containers
heat cannot penetrate to center fast enough, slower
surface VERY OVERCOOKED
How are plastic trays sealed?
Thermostable plastic film
What are some non-can containers used in processing that are good for HTST?
retort pouches
semi-rigid plastic trays
How are plastic pouches and trays added to the retort?
Restrained in compartments/perforated holders
Prevent movement and keep uniformity
True/False: a thin package does not require thermocouple monitoring.
False: will still have a cold point (in center)
The retort pouch has ___ layers; describe their functions.
3
outer layer: durability/printability
middle layer: aluminum, barrier
inner layer: heat sealed, contacts food (food safe)
What provides overpressure?
Air
What determines the degree of overpressure?
PROPORTION of air/steam
Overpressure processing, in the heat mediums ____ and ____, is necessary for what types of product packages?
steam/air, water/air
glass, flexible container, pouches
More air will increase:
More steam will increase:
more air -> more overpressure protection
more steam -> better heat transfer rate
The danger zone (risk of pack bursting) is when the retort pressure is (above/below) the _____
below; package pressure
What is absolutely required if using overpressure methods?
turbulent conditions
fan or continuous venting
Why is overpressure needed for plastic packs but not cans?
plastic seams are weaker when heated, without excess pressure on outside (overpressure from air) the seams may burst
The purpose of overpressure is to:
This is accomplished by:
maintain package integrity
preventing pressure build up (especially during cooling)
The most common steam/air ratio is:
75/25
What other method works in a similar way to overpressure to maintain package integrity?
compressing between plates
What type of heating is improved by agitation?
convection
what does “k” represent?
thermal conductivity
What are the 3 main methods of processing associated with quality optimization?
Thin Profile
Rotation/Agitation
Aseptic
What are some disadvantages of pouches?
What is the improved alternative?
package failures (fragile)
need overpressure
slower sealing
more labor needed
incomplete air removal (so requires overpressure)
Alternative: plastic trays (rigid, also microwaveable!)
How does agitation improve heat transfer? (2)
mixing
increase heat transfer coefficient (h)
What are the 3 types of agitation?
end over end
axial
reciprocation
The main advantages of HTST:
high quality
convenience (lightweight, easy disposal/opening/storage/use)
The critical factors affecting rotary processing: (6)
solid/liq ratio headspace size temperature consistency container size/type speed of agitation
what product types have succesfully used aseptic processing?
liquids, acid/acidified particulate foods
continuous processes use ____ agitation, while batch uses ____ agitation.
axial; end over end
End over end agitation works well for what packages?
cans, semi rigid packages, glass
Describe reciprocation agitation and what it is applicable for.
shaking
all containers
___ agitation only works for cans.
axial
What products are not suitable for aseptic processing?
conductive heating types (solids)
A disadvantage of aseptic is that it is long enough to kill microbes, but not long enough to: ____
inactivate enzymes
What additional benefits does aseptic processing have, compared to thin profile and rotary?
- lower energy consumption
- continuous
- can be adapted to automatic controls
what was recognized by IFT as the most significant innovation in the past 50 years?
Aseptic processing
The 3 main parts of aseptic processing:
Sterilize food
sterilize package
fill/seal in sterile environment
What are the temperature ranges and times for acid and low acid foods in aseptic processing?
acid: 93-96C for 15-30s
low acid: 138-149C for 1-30s
How is aseptic equipment sterilized?
Steam, water, strong alkali (clean in place)
What must be kept sterile during aseptic processing?
food, package, equipment
and environment
Foods like vegetables and viscous sauces can be problematic in aseptic processing, and are known as:
low acid particulate foods
How is the package sterilized in aseptic processing?
Steam, hot air (not applicable for all)
H peroxide, UV, irradiation, co-extrusion
What shape/size of particle would move faster?
spherical, larger size
can roll along, larger surface area to be pushed
What type of heat exchanger is used with low acid particulate foods?
SSHE
Why are particulate foods problematic?
hard to measure temp of moving particle
need to determine heat transfer from liquid to particles
effects of particle size/speed/shape
particles may not be uniform!
Is lower or higher viscosity fluid better at giving flow to particulates?
Higher
Describe the differences between laminar and turbulent flow.
laminar: river like, particles do not interfere w/ each other, smooth paths
turbulent: many little whirlpools, irregular flow
How does average velocity and velocity distribution differ in laminar and turbulent flow?
laminar: higher average velocity (velocity very constant throughout)
turbulent: wide distribution of velocities, not constant
