Food Biochemistry and Food Processing (2 edition)

BLBS102-c38 BLBS102-Simpson March 21, 2012 14:17 Trim: 276mm X 219mm Printer Name: Yet to Come

736 Part 7: Food Processing

0 1224364860728496

Temperature (°C)

Time (min)

21

111

120

-79

-879

Tr-1

Tr-10

Tr-100

Tr-1000

T Tr-T

One log cycle on 3 log cycle paper

Figure 38.6.Diagram showing how the axis of semi-logarithmic graphing paper (rotated 180◦C) is marked for plotting heat penetration data

for retort temperature of 121◦C.

0 12 24 36 48 60 72 84 96

Temperature (°C)

Time (min)

21

111

120

-79

-879

fh

Tih

Tpih

TR-1

TR-10

TR- 100

TR-1000

T Tr-T

58% of CUT

Figure 38.7.Heat penetration curve on semi-log paper during

heating phase.

heating medium to when processing temperature (Tr) is reached

is the retort CUT. Among his several assumptions, Ball (1923)

assumed that 58% of the retort CUT has no significant heating

or lethality value; therefore, heating starts from a pseudo-initial

time (tpih), which is 058% of CUT (0.58 CUT). According to

Figure 38.7, the total CUT is assumed as 12 minutes. Therefore,

the corrected zero time or pseudo-initial time (tpih) is 7 minutes

(0.58∗12). From hypothetical data of Figure 38.7, the heating

parameters ofjhandfhare

jh=

Tr−Tpih

Tr−Tih

=

121 − 61

121 − 71

= 1 .2and,

fh= 74. 4 − 14. 4 =60 minutes

The heating rate index (fh−value) is obtained as the time for

the curve to traverse one logarithmic cycle (Fig. 38.7).

For cooling part, to plot the cooling curve on semi-log paper

(in this case you do not need to rotate 180◦), the bottom line is

marked 1◦C, the second log cycle 10◦C, and the third log cycle

100 ◦C above the cooling water temperature (Figure 38.8). Then,

temperatures are plotted directly on they-axis of semi-log paper

and time of cooling onx-axis. Cooling parameters,fcandjcc,

(Equation 35) are obtained likewise during heating, except there

are no come-down time considerations during cooling.

In addition to this, the cooling curve can be obtained by plot-

ting a cooling curve graph from log difference of temperature

of a product to that of cooling water temperature (log(T−Tcw))