Lecture 6: Heat Penetration Behaviour (Formula Methods) Flashcards Preview

4) Food Processing > Lecture 6: Heat Penetration Behaviour (Formula Methods) > Flashcards

Flashcards in Lecture 6: Heat Penetration Behaviour (Formula Methods) Deck (45)
Loading flashcards...
1
Q

what are uses of general method?

A

graphical or numerical integration of heat penetration curve

2
Q

how do you use the formula method

A
  • use heat penetration parameters from the heat penetration curve
  • integrate destruction kinetics with heat penetration parameters
3
Q

what is transient time

A

temp data obtained at the cold spot location in the container during a process test

4
Q

in heating and cooling curves, temp and time have a ___ relationship

A

semi log

5
Q

in heating and cooling curves, log (temp) vs time have a ____ relationship

A

linear

6
Q

what defines the intercept of the heating curve?

A

log (Tr-Tpih)

7
Q

what is Tr?

A

retort temp

8
Q

what is Tih?

A

product initial temp

9
Q

what is T?

A

product temp at time t

10
Q

what is Tpih?

A

pseudo initial temperature (intercept of the straight line)

11
Q

what defines where the process actually starts?

A

log (Tr-Tih)

12
Q

define the slope of the heating curve

A

[log(Tr-T1) - log (Tr-T2)]/ (t1-t2)

13
Q

what is fh?

A

heating rate index (the time to pass one log cycle)

14
Q

in the heating curve, what is slope defined as?

A

slope = - 1/fh

15
Q

what is jch?

A

lag factor

jch = (Tr-Tpih) / Tr-Tih)

16
Q

what is g?

A

Tr - T

17
Q

what is Ih?

A

Tr - Tih (temp difference during heating)

18
Q

what is Tw?

A

water temperature

19
Q

what is Tic?

A

product initial cooling temp

20
Q

what represents the intercept of straight portion of the cooling curve?

A

log (Tpic-Tw)

21
Q

what defines the slope of the cooling curve?

A

slope = -1/fc

22
Q

what defines the point where the process actually starts?

A

log (Tic-Tw)

23
Q

what is Tpic?

A

pseudo initial cooling temp (the point where the linear portion of the cooling curve is a zero)

24
Q

what does Fc = Fh mean?

A

the product is heating and cooling at the same rate

25
Q

what is CUT?

A

come up time

  • the time to reach the operating temperature
  • not the same as processing time
  • contributes to some warming of the product
  • using some of the CUT can reduce the process time
26
Q

when can you ignore CUT?

A

as a safety factor, CUT can be ignored

27
Q

how much of the CUT did Ball determine to be effective?

A

the last 42% of CUT is effective and can be used as processing time

28
Q

how much of the CUT did Ball determine to be NOT effective?

A
  • the first 58% of CUT

- should be discarded

29
Q

if your CUT is 10 mins, ____ is not useful

A

first 6 mins

30
Q

the come up time means the time scale should be shifted _____

A

forward

eg. shift the Xzero to the new point at X = 0.58CUT

31
Q

how are cooling curves affected by CUT?

A

cooling curves are not adjusted because cooling times are not used in process calculations

32
Q

what is B? what does this include? what equation represents this?

A

ball process time

includes: effective portion of the CUT + operators process time

B = Pt + 0.42CUT

33
Q

what is Pt?

A

operator’s process time

the total heating time - CUT

34
Q

what is the ball formula method based on?

A

heat penetration curve

35
Q

what is Bb

A

ball’s process time

36
Q

what is considered an industry standard?

A

ball formula method

37
Q

what are 4 assumptions made in the ball method?

A
  1. z = 18F
  2. heating rate index (fh) = cooling rate index (fc)
  3. cooling curve lag factor: jcc = 1.41
  4. CUT effectiveness = 42%
38
Q

what is used to related heating to lethality?

A

ball tables related Fh/U to log(g)

39
Q

when should you not use the ball method? why?

A

when Fh > Fc

ie. when cooling is faster than heating

using ball method would underestimate

40
Q

when jcc < 1.41, what method should you use?

A

ball

41
Q

when jcc = 1.41, what method should you use?

A

doesn’t matter

42
Q

if jcc > 1.41, what method should you use?

A

stumbo

the ball method would underestimate the processing time

43
Q

what is the stumbo method based on?

A
  • heating and cooling curves
  • jcc and jch values
  • assumes Fh = Fc
44
Q

in the stumbo method, Fh = what?

A

Fh = Fc

45
Q

when Fh > Fc, what method should you use?

A

general methods