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food processing > Thermal Processing Calculations (General and Formula) > Flashcards

Thermal Processing Calculations (General and Formula) Flashcards

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1
Q

The period in which the temperature of the retort rises is known as:

A

the Come Up Time (CUT)

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2
Q

Compare the differences between destruction kinetics and real life thermal processing conditions. (4)

A
  1. destruction kinetics has SMALL SAMPLE: very little lag, almost instant come up/down (while cans are much larger and have bigger lag)
  2. Constant temperature while in thermal processing wide range of temperatures
  3. pre-stabilized water bath vs heated retorts (with CUT)
  4. Need to INTEGRATE heating over entire period for thermal processing
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3
Q

True/False: in thermal processing the temperature of the retort and product will heat at the same rate

A

False: the retort will heat up faster

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4
Q

What does Fo represent? (2)

A 
Reference TDT (at 250F)
OR
Process Lethality (equivalent heating time at 250F expressed in minutes)
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5
Q

What equation can be used to determine equivalent heating times at different temperatures?

A

F = Fo*10^[(250-T)/z]

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6
Q

how are k and D related to the survivor curve?

A 
k = negative slope
D = negative reciprocal slope
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7
Q

When describing a certain “F,” what pieces of information are given?

A 
Temperature (subscript)
z value (superscript)
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8
Q

Why is there a delay in heating the product? what is this called?

A

LAG: due to larger can size, heat needs to fully penetrate, retort needs to reach temperature

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9
Q

What is done to take measurements and ensure sufficient heating of the product?

A

Thermocouple at COLD POINT: coldest point must reach temperature

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10
Q

What are the 2 main types of heat penetration?

A

convection

conduction

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11
Q

How does thermocouple placement vary, and why?

A

Convection: 1/10th of height, near bottom (due to rising warm currents and sinking cold currents)
Conduction: near centre (heat penetrates from all surfaces, centre is furthest)

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12
Q

How is Fo different for destruction kinetics and thermal process calculations?

A

In destruction kinetics, it is the reference TDT at 250F, can be used to calculate the lethality at other temperatures

In process calculations, it refers to the PROCESS LETHALITY, the integrated sum of the whole process (sum of all the times at various temperatures throughout)
This is expressed in terms of MINUTES @ 250F

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13
Q

What determines whether the heating pattern will be convection or conduction?

A

State of product; convection is for liquid, conduction is for solids

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14
Q

When might convection-conduction heating occur?

A

Starch containing slurries (thickens)

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15
Q

Describe the difference between convection vs conduction heating - which is faster?

A

Conduction is heat transferred from particle to particle, in tightly packed solid foods, with heating from all sides
Convection is in liquid foods, and heating will cause CURRENTS: heated liquid will become less dense and rise, as it cools it will sink (heart shaped current)
convection is FASTER.

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16
Q

What factors affect the heating temperature profile? (5)

A
  • Heating conditions
  • Heating medium
  • Container
  • Product type
  • Heating process
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17
Q

When might conduction-convection heating occur?

A

Fatty products - solid becomes liquid

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18
Q

The primary and secondary objectives of thermal processing are:

A

safety; quality

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19
Q

How could you increase the heating rate of a product?

A

Increase surface area, use steam rather than air, agitation

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20
Q

Would a liquid or solid product of equal volume/weight be slower to heat (under similar conditions)?

A

Solid

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21
Q

What approaches are taken to 1. ensure safety, and 2. maintain highest quality possible?

A
  1. monitor temperature at coldest point to ensure entire can has reached necessary lethality
  2. integrate lethality over entire process to prevent overcooking (minimize bulk cooking)
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22
Q

The 2 types of thermal process calculation are:

A
  1. Process Establishment

2. Process Verification

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23
Q

What are PE and PV calculations determining?

A

PE: how long of a process time is needed for given lethality
PV: lethality of a given process

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24
Q

What are the 3 main methods of process calculation?

A

General Method
Formula methods
Numerical methods

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25
Q

What are some examples of formula methods?

A

Ball, Stumbo, pham, hayakawa

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26
Q

What studies are done to confirm if the calculated process time is actually sufficient?

A

Inoculated pack studies

Time-temperature integration

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27
Q

The ____ _____ data and ____ _____ are combined to calculate the theoretical process ____.

A

heat penetration; TDT kinetics

time

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28
Q

In the general method: The reciprocal of ____ represents the rate of destruction

A

TDT

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29
Q

What data is needed for the general method?

A

TDT, z for organism

time-temp data for product

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30
Q

When would the destruction process be considered complete, in terms of the general method?

A

When SV = 1 (t = TDT)

31
Q

What is SV? How is it derived?

A

Sterilization Value:
sum of EXTENT OF DESTRUCTION at each temperature
sum of all [(1/TDT)*t]

32
Q

What was the earliest process calculation method, that formed the basis for all others?

A

General method

33
Q

True/False: SV is expressed in minutes

A

False: SV has NO UNITS

34
Q

The SV value is usually 1 + a ______ ______.

A

safety margin

35
Q

Graphical integration is represented by the _____.

A

area under the curve.

36
Q

When t = TDT, then SV = ?

A

1

37
Q

An SV of 2 would be a safety margin of ____.

A

100%

38
Q

What non-calculus approaches may be used to integrate the curve?

A

Approximating (triangle)
Cut and weight graph paper to determine area
Planimeter
Numerical integration

39
Q

True/False: An SV value of 12 is necessary to kill C. botulinum

A

False: SV of 12 is likely too high (12 x TDT), result in overcooking

40
Q

The general method ultimately calculates ____ by integration of the ______ vs ____ curve.

A

SV; 1/TDT vs time

41
Q

What is the L value?

A

Lethal Rate

42
Q

How does the improved general method differ from the original?

A

Assume Fo = 1 min

43
Q

How might the accuracy of the numerical integration in the general method be improved?

A

More data points (shorter time intervals between measurements)

44
Q

What does Lethal Rate represent?

A

number of EQUIVALENT minutes at 250F

for certain number of min at retort temperature

45
Q

How is L value calculated?

A

Fo/F or 1/TDT (assume Fo=1 min)

46
Q

Integrating the lethal rate vs time graph will give:

A

PROCESS LETHALITY (equivalent minutes at 250F for entire process)

47
Q

True/False: a change in retort conditions will require recalculating process lethality

A

True: changes in initial temp or retort temp, etc, will require recalculating with new data

48
Q

The advantage of the improved general method is:

A

applicable for many microorganisms (in terms of minutes at 250F) while the original method expressed as SV, which is specific for that organism

49
Q

If the initial temp or retort temp changes, how can the original data be used to calculate the new lethality?

A

Use conversion formula to obtain new theoretical temperature data and recalculate.

50
Q

The temperature-time curve is non-____ and requires _____ for the formula method

A

linear; linearization

51
Q

The linearized slope of the heating curve is straight except in ____

A

the lag portion

52
Q

How is the heating/cooling curve linearized?

A

Express as LOGARITHMIC curve

heating: log (Tr-T) vs time
cooling: log (T-Tw) vs time

53
Q

When gathering heat penetration data, the temperature at the cold spot is monitored to determine:

A

transient time

54
Q

At time zero, the heating curve (theoretical) intercept is _____.

A

log(Tr-Tpih)

55
Q

How does the theoretical intercept of the heating/cooling curve differ from the actual?

A

The actual initial curve will have lag; the actual initial temperature during heating will be lower, while the initial cooling temp will be higher

56
Q

What does “f” represent for heating/cooling curves?

A

the heating/cooling index

time needed to pass 1 LOG CYCLE

57
Q

What is the come up time?

A

time needed for retort to reach operating temp

58
Q

What is the slope of the cooling curve?

A

-1/fc

59
Q

True/False: Tr is constant through the heating process

A

False: Tr is not instantaneous, retort needs time to heat up (during CUT, temp is lower)

60
Q

Ball determined that ___% of the CUT is effective and can be used as part of processing time

A

42%

61
Q

Which is longer, Ball or operator processing time?

A

Ball; takes into account the effective portion of CUT

62
Q

What is Ball processing time?

A

operator’s time + 0.42CUT

63
Q

What symbol represents lag factor?

A

j

64
Q

Because the first ___% of the CUT is ineffective, what needs to be done?

A

58%; Shift time scale forward, to start process time at 58% of CUT

65
Q

define operator’s time

A

processing time from when retort reaches temperature setpoint (total time - CUT)

66
Q

Shifting the process time forward to account for CUT will affect the ____ but not ____.

A

jch, fh

67
Q

What is U?

A

Fi*Fo

lethality at retort temp x process lethality

68
Q

What assumptions are made by the Ball method? (4)

A

z = 18F
fh = fc
jcc = 1.41
0.42 CUT is effective

69
Q

What would happen is fh =/= fc? Why is it usually safe to assume that fh = fc?

A

fh < fc -> longer actual heating time
fh > fc -> shorter actual heating time
cooling time usually takes longer than heating ( fc > fh), so more heat is applied than calculated making it still safe

70
Q

When would Ball method not be safe to use? Why?

A

if jcc < 1.41

Ball method would lead to less heating time than calculated (smaller cooling curve), may not reach necessary lethality

71
Q

Why might the Ball method be less accurate?

A

Makes assumptions, does not use cooling curve

72
Q

When would neither Ball nor Stumbo methods be applicable? What method can be used then?

A

When fc

73
Q

What is the main difference between Ball and Stumbo methods?

A

Stumbo uses jch and jcc, Ball only use jch

Stumbo takes into account different z values, Ball assume z = 18F

food processing (17 decks)

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