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food processing > Thermal Processing Quality Optimization > Flashcards

Thermal Processing Quality Optimization Flashcards

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1
Q

What type of heat transfer occurs between the medium and the can?

A

Convection

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2
Q

What are the benefits of improved heat transfer rate?

A
  • Faster turnover (shorter process time)
  • heating uniformity
  • Less overcooking
  • Better quality
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3
Q

To optimize quality of the product, we need to (increase/decrease) processing time by improving ____.

A

Decrease

Heat transfer

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4
Q

What is the formula for convection heating?

A

q = hAΔT

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5
Q

Where does heat transfer occur between during processing? (2)

A

medium -> can

within can contents

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6
Q

What is the formula for conduction heating?

A

q = (kAΔT)/x

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7
Q

List spores, nutrients, and bacteria in order of increasing D value.

A

bacteria, spores, nutrients

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8
Q

The driving force of improving quality retention is:

A

improving RATE OF HEAT TRANSFER

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9
Q

True/False: nutrients have a higher D value but a lower z value than bacteria

A

False: higher D, and ALSO HIGHER Z

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10
Q

List 3 types of heat exchangers:

A

Scraped surface
Tubular
Plate and Frame

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11
Q

Why would short time, high temperature processing be better than longer lower temperatures at retaining nutrient quality?

A

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

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12
Q

The flow of product and medium in plate exchangers is usually ____.

A

Countercurrent

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13
Q

Describe each heat exchange system:

A

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

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14
Q

What systems work well with quality optimization? (2)

A
  • In container sterilization

- Continuous Processing system (work very well)

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15
Q

In tube heat exchangers, the flow is _____

A

either countercurrent or cross current

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16
Q

What process parameters are very compatible with HTST or UHT?

A
  • liquids (or liquids with small particles)
  • thin packages
  • processes with agitation
  • continuous (aseptic)
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17
Q

Why would a flat product be faster in conductive heating? (2)

A 
increased surface area (A)
decreased thickness (x)
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18
Q

What is HTST NOT suitable for? Why?

A

conduction heating, especially large containers
heat cannot penetrate to center fast enough, slower
surface VERY OVERCOOKED

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19
Q

How are plastic trays sealed?

A

Thermostable plastic film

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20
Q

What are some non-can containers used in processing that are good for HTST?

A

retort pouches

semi-rigid plastic trays

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21
Q

How are plastic pouches and trays added to the retort?

A

Restrained in compartments/perforated holders

Prevent movement and keep uniformity

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22
Q

True/False: a thin package does not require thermocouple monitoring.

A

False: will still have a cold point (in center)

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23
Q

The retort pouch has ___ layers; describe their functions.

A

3
outer layer: durability/printability
middle layer: aluminum, barrier
inner layer: heat sealed, contacts food (food safe)

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24
Q

What provides overpressure?

A

Air

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25
Q

What determines the degree of overpressure?

A

PROPORTION of air/steam

26
Q

Overpressure processing, in the heat mediums ____ and ____, is necessary for what types of product packages?

A

steam/air, water/air

glass, flexible container, pouches

27
Q

More air will increase:

More steam will increase:

A

more air -> more overpressure protection

more steam -> better heat transfer rate

28
Q

The danger zone (risk of pack bursting) is when the retort pressure is (above/below) the _____

A

below; package pressure

29
Q

What is absolutely required if using overpressure methods?

A

turbulent conditions

fan or continuous venting

30
Q

Why is overpressure needed for plastic packs but not cans?

A

plastic seams are weaker when heated, without excess pressure on outside (overpressure from air) the seams may burst

31
Q

The purpose of overpressure is to:

This is accomplished by:

A

maintain package integrity

preventing pressure build up (especially during cooling)

32
Q

The most common steam/air ratio is:

A

75/25

33
Q

What other method works in a similar way to overpressure to maintain package integrity?

A

compressing between plates

34
Q

What type of heating is improved by agitation?

A

convection

35
Q

what does “k” represent?

A

thermal conductivity

36
Q

What are the 3 main methods of processing associated with quality optimization?

A

Thin Profile
Rotation/Agitation
Aseptic

37
Q

What are some disadvantages of pouches?

What is the improved alternative?

A

package failures (fragile)
need overpressure
slower sealing
more labor needed
incomplete air removal (so requires overpressure)
Alternative: plastic trays (rigid, also microwaveable!)

38
Q

How does agitation improve heat transfer? (2)

A

mixing

increase heat transfer coefficient (h)

39
Q

What are the 3 types of agitation?

A

end over end
axial
reciprocation

40
Q

The main advantages of HTST:

A

high quality

convenience (lightweight, easy disposal/opening/storage/use)

41
Q

The critical factors affecting rotary processing: (6)

A 
solid/liq ratio
headspace size
temperature
consistency
container size/type
speed of agitation
42
Q

what product types have succesfully used aseptic processing?

A

liquids, acid/acidified particulate foods

43
Q

continuous processes use ____ agitation, while batch uses ____ agitation.

A

axial; end over end

44
Q

End over end agitation works well for what packages?

A

cans, semi rigid packages, glass

45
Q

Describe reciprocation agitation and what it is applicable for.

A

shaking

all containers

46
Q

___ agitation only works for cans.

A

axial

47
Q

What products are not suitable for aseptic processing?

A

conductive heating types (solids)

48
Q

A disadvantage of aseptic is that it is long enough to kill microbes, but not long enough to: ____

A

inactivate enzymes

49
Q

What additional benefits does aseptic processing have, compared to thin profile and rotary?

A
  • lower energy consumption
  • continuous
  • can be adapted to automatic controls
50
Q

what was recognized by IFT as the most significant innovation in the past 50 years?

A

Aseptic processing

51
Q

The 3 main parts of aseptic processing:

A

Sterilize food
sterilize package
fill/seal in sterile environment

52
Q

What are the temperature ranges and times for acid and low acid foods in aseptic processing?

A

acid: 93-96C for 15-30s

low acid: 138-149C for 1-30s

53
Q

How is aseptic equipment sterilized?

A

Steam, water, strong alkali (clean in place)

54
Q

What must be kept sterile during aseptic processing?

A

food, package, equipment

and environment

55
Q

Foods like vegetables and viscous sauces can be problematic in aseptic processing, and are known as:

A

low acid particulate foods

56
Q

How is the package sterilized in aseptic processing?

A

Steam, hot air (not applicable for all)

H peroxide, UV, irradiation, co-extrusion

57
Q

What shape/size of particle would move faster?

A

spherical, larger size

can roll along, larger surface area to be pushed

58
Q

What type of heat exchanger is used with low acid particulate foods?

A

SSHE

59
Q

Why are particulate foods problematic?

A

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!

60
Q

Is lower or higher viscosity fluid better at giving flow to particulates?

A

Higher

61
Q

Describe the differences between laminar and turbulent flow.

A

laminar: river like, particles do not interfere w/ each other, smooth paths
turbulent: many little whirlpools, irregular flow

62
Q

How does average velocity and velocity distribution differ in laminar and turbulent flow?

A

laminar: higher average velocity (velocity very constant throughout)
turbulent: wide distribution of velocities, not constant

food processing (17 decks)

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