Thermal Processing Calculations (General and Formula)

Question 1

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

Answer 1

the Come Up Time (CUT)

Question 2

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

Answer 2

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

Question 3

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

Answer 3

False: the retort will heat up faster

Question 4

What does Fo represent? (2)

Answer 4

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

Question 5

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

Answer 5

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

Question 6

how are k and D related to the survivor curve?

Answer 6

k = negative slope
D = negative reciprocal slope

Question 7

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

Answer 7

Temperature (subscript)
z value (superscript)

Question 8

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

Answer 8

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

Question 9

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

Answer 9

Thermocouple at COLD POINT: coldest point must reach temperature

Question 10

What are the 2 main types of heat penetration?

Answer 10

convection

conduction

Question 11

How does thermocouple placement vary, and why?

Answer 11

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)

Question 12

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

Answer 12

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

Question 13

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

Answer 13

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

Question 14

When might convection-conduction heating occur?

Answer 14

Starch containing slurries (thickens)

Question 15

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

Answer 15

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.

Question 16

What factors affect the heating temperature profile? (5)

Answer 16

• Heating conditions
• Heating medium
• Container
• Product type
• Heating process

Question 17

When might conduction-convection heating occur?

Answer 17

Fatty products - solid becomes liquid

Question 18

The primary and secondary objectives of thermal processing are:

Answer 18

safety; quality

Question 19

How could you increase the heating rate of a product?

Answer 19

Increase surface area, use steam rather than air, agitation

Question 20

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

Answer 20

Solid

Question 21

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

Answer 21

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)

Question 22

The 2 types of thermal process calculation are:

Answer 22

1. Process Establishment

2. Process Verification

Question 23

What are PE and PV calculations determining?

Answer 23

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

Question 24

What are the 3 main methods of process calculation?

Answer 24

General Method
Formula methods
Numerical methods

Question 25

What are some examples of formula methods?

Answer 25

Ball, Stumbo, pham, hayakawa

Question 26

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

Answer 26

Inoculated pack studies | Time-temperature integration

Question 27

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

Answer 27

heat penetration; TDT kinetics | time

Question 28

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

Answer 28

TDT

Question 29

What data is needed for the general method?

Answer 29

TDT, z for organism | time-temp data for product

Question 30

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

Answer 30

When SV = 1 (t = TDT)

Question 31

What is SV? How is it derived?

Answer 31

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

Question 32

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

Answer 32

General method

Question 33

True/False: SV is expressed in minutes

Answer 33

False: SV has NO UNITS

Question 34

The SV value is usually 1 + a ______ ______.

Answer 34

safety margin

Question 35

Graphical integration is represented by the _____.

Answer 35

area under the curve.

Question 36

When t = TDT, then SV = ?

Answer 36

1

Question 37

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

Answer 37

100%

Question 38

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

Answer 38

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

Question 39

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

Answer 39

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

Question 40

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

Answer 40

SV; 1/TDT vs time

Question 41

What is the L value?

Answer 41

Lethal Rate

Question 42

How does the improved general method differ from the original?

Answer 42

Assume Fo = 1 min

Question 43

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

Answer 43

More data points (shorter time intervals between measurements)

Question 44

What does Lethal Rate represent?

Answer 44

number of EQUIVALENT minutes at 250F | for certain number of min at retort temperature

Question 45

How is L value calculated?

Answer 45

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

Question 46

Integrating the lethal rate vs time graph will give:

Answer 46

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

Question 47

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

Answer 47

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

Question 48

The advantage of the improved general method is:

Answer 48

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

Question 49

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

Answer 49

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

Question 50

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

Answer 50

linear; linearization

Question 51

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

Answer 51

the lag portion

Question 52

How is the heating/cooling curve linearized?

Answer 52

Express as LOGARITHMIC curve heating: log (Tr-T) vs time cooling: log (T-Tw) vs time

Question 53

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

Answer 53

transient time

Question 54

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

Answer 54

log(Tr-Tpih)

Question 55

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

Answer 55

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

Question 56

What does "f" represent for heating/cooling curves?

Answer 56

the heating/cooling index | time needed to pass 1 LOG CYCLE

Question 57

What is the come up time?

Answer 57

time needed for retort to reach operating temp

Question 58

What is the slope of the cooling curve?

Answer 58

-1/fc

Question 59

True/False: Tr is constant through the heating process

Answer 59

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

Question 60

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

Answer 60

42%

Question 61

Which is longer, Ball or operator processing time?

Answer 61

Ball; takes into account the effective portion of CUT

Question 62

What is Ball processing time?

Answer 62

operator's time + 0.42CUT

Question 63

What symbol represents lag factor?

Answer 63

j

Question 64

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

Answer 64

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

Question 65

define operator's time

Answer 65

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

Question 66

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

Answer 66

jch, fh

Question 67

What is U?

Answer 67

Fi*Fo | lethality at retort temp x process lethality

Question 68

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

Answer 68

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

Question 69

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

Answer 69

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

Question 70

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

Answer 70

if jcc < 1.41 | Ball method would lead to less heating time than calculated (smaller cooling curve), may not reach necessary lethality

Question 71

Why might the Ball method be less accurate?

Answer 71

Makes assumptions, does not use cooling curve

Question 72

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

Answer 72

When fc

Question 73

What is the main difference between Ball and Stumbo methods?

Answer 73

Stumbo uses jch and jcc, Ball only use jch | Stumbo takes into account different z values, Ball assume z = 18F