Modernist-Cuisine-Vol.-1-Small

Visualizing Thermal Death Curves
A common assumption in food science is that the same fraction of the
Number of bacteria per ml (millions)
Number Number of bacteria of bacteria per ml per (millions) ml (millions)
Number Number of bacteria of bacteria per ml per (millions)
ml (millions)
Number Tenfold
Number
of bacteria reduction
of bacteria
per time ml
per
(millions) D
ml
(min)
(millions)
D At 70 ˚C / 158 ˚F,
20
ref
0.1
At 65 ˚C / 149 ˚F,
At 60 ˚C / 140 ˚F,
ref
= 5 min
D ref
= 10 min
D
1
1
ref
= 15 minutes
At 60 ˚C / 140 ˚F,
0 10 20 30 40 50 1
D 00 10 20 30 40 50
ref
= 15 minutes
15 30 45
01
Cooking time (minutes)
0.01 0.1
Cooking time (minutes)
0 10 15 20 30 40 45 50
Cooking time (minutes)
55 0
57 5559 61 6063 65 65
67 6970
Cooking time (minutes)
Cooking Temperature temperature (˚C) (˚C)
The time D is the number of minutes needed to reduce
As the actual data points from scientific studies show below, thermal
the bacteria count to one-tenth the starting number (by 90%)
death curves vary from one kind of pathogen and food to another
The death curve becomes a straight line when
The higher the cooking temperature, the faster
100
Temperature (˚F)
150 bacteria counts are expressed as powers of 10 VOLUME 1 · HISTORY AND FUNDAMENTALS
bacteria die, and the shorter the D time
131 134.6 138.2 141.8 145.4 149 152.6 156.2˚F
100
100
When cooked
at 60˚C, the
illions)
Number of bacteria per ml (millions)
Tenfold reduction time D (min)
Decimation Ten-fold Number Number reduction time
of of bacteria bacteria D time (minutes) D per per (min) ml ml (millions) (millions)
1
Numbe
Number of bacteria per ml (millions)
Number of bacteria per ml (millions)
20
0
0 10 20 30 40 50
Cooking time (minutes)
Tenfold reduction time D (min)
Number of bacteria per ml (millions)
Decimation time D (minutes)
Tenfold Num
Number of bacteria per ml (millions)
Decimation time D (minutes)
1
0.1 0 10 20 30 40 50
55 60 65 70
Cooking time (minutes)
Cooking temperature (˚C)
Num
Decimation time D (minutes)
At 70 ˚C / 158 ˚F, At 65 ˚C / 149 ˚F,
D ref
= 5 min
D ref
= 10 min
1
0 10 20 30 40 50
Cooking time (minutes)
number of minutes needed at a given The death temperature curve becomes to knock a the straight population line when
The higher time D the is the cooking number temperature, of minutes the needed faster to reduce
As the actual data points from scientific studies show below, thermal
Bacteria die at an exponential rate; the curve shows the number
bacteria in a particular food held at a particular temperature dies off each down to one-tenth its starting number. bacteria That counts time are falls expressed as temperature as powers rises, of 10
bacteria the bacteria die, count and the to shorter one-tenth the the D time starting number (by 90%)
death curves vary from one kind of pathogen and food to another
remaining alive over time
A graph of D vs temperature reveals how long you must hold food at
minute. Bacteria That means, die at for an example, exponential that rate; if 90% the of curve the bacteria shows the die number in the first and when the time D is plotted 100against temperature on a graph that has
100
Temperature (˚F)
100
a given temperature to achieve a tenfold (1D) reduction in bacteria
7 min at remaining 58 °C / 136 alive °F, then over 90% timeof those that remain die in the next 7 min, powers of A 10 graph on the of D vertical vs temperature axis, the reveals result is how usually long a you straight must line hold (top food right at
131 134.6 138.2 141.8 145.4 149 152.6 156.2˚F
100
and so 100on. In other words, the population falls exponentially over time, as chart below).
a given
The
temperature
rate of killing
to achieve
can then
a
be
tenfold
summarized
(1D) reduction
with just
in bacteria
the four
131 When 140 cooked 149
158˚F
shown in the top left chart below. The shape of this “thermal death curve” parameters defined in the table Thermal Death Curve Parameters immediately
100 below.
drops from
15 minutes, it
100
at 60˚C, the
80
131 140 149
158˚F
bacteria count
...and in the next
can be summarized by a power of 10 (a logarithm) called D, which is the
80
Death curve at temperature T 100 million to
drops another 90%
ref
10
10 million
from 10 million
At Tin ref
= 1558 minutes... ˚C / 136 ˚F,
At 60 ˚C / 140 ˚F,
Death curve at temperature T
to one million
ref
60
D ref
= 15 min
10
10
D 10
ref
= 7 minutes
At T ref
= 58 ˚C / 136 ˚F,
Thermal 60 Death Curve Parameters
1
10
D ref
= 7 minutes
Parameter Definition
40
At T ref
= 65 ˚C / 149 ˚F,
T min
40
minimum temperature needed to kill the organism (at least within the boundaries
D
1
D ref
ref
= 36 seconds
0.1
of the study)
At T ref
= 65 ˚C / 149 ˚F,
201
D ref
= 36 seconds
At At 7060 ˚C ˚C / 158 / 140 ˚F, ˚F, At 65 ˚C / 149 ˚F,
D ref
time needed to kill 90% of organisms at the reference temperature (for a 1D drop)
D ref
D= ref
5 = min 15 minutes D ref
= 10 min
20
1
1
0.01
T 0 10 20 30 40 50
0 10 15 20 30 ref
reference temperature at which D ref
is measured
40 45 50
55 57 59 61 63 65 67 69
0
0.1
Z change in temperature required to reduce the D value by a factor of 0 10 10 20 30 Cooking 40 time (minutes) 50
0 55 60 Cooking 65 time (minutes) 70
Temperature (˚C)
0
0.1
0 10 20 30 40 50
0 55 Cooking time 60(minutes)
65 70
Cooking temperature (˚C)
Bacteria die at an exponential Cooking rate; time the (minutes) curve shows the number
Cooking The time temperature D is the number (˚C) of minutes needed to reduce
As the actual data points from scientific studies show below, thermal
remaining alive over time
The A graph death of curve D vs becomes temperature the a straight bacteria reveals line how count when long to one-tenth you must hold the starting food at number (by 90%) The higher the cooking temperature, death curves the vary faster from one kind of pathogen and food to another
100
bacteria a given counts temperature are expressed to 100achieve as a powers tenfold of (1D) 10 reduction in bacteria
bacteria die, and the shorter the D time
Temperature (˚F)
The death curve becomes a straight line when
The higher the cooking temperature, the faster
100
100
The graph 131below shows 134.6 thermal 138.2death curves 141.8 from 145.4 the scientific 149literature 152.6 for a 6.5D 156.2˚F
bacteria counts are expressed as powers of 10
bacteria die, and the shorter the D time
For example, E. coli is more heat sensitive than Salmonella. The Salmonella curve in red
131 140 149
158˚F
100
reduction of various pathogens: Salmonella spp. (red, a composite), Campylobacter jejuni
100
100
When cooked
is the basis for FDA cooking guidelines for many foodborne pathogens (see chapter 3)
at 60˚C, the
80
(blue), E. coli (green), and Trichinella spiralis (black). The lines cover the range of
bacteria count
...and in the next
because it is a serious threat in its own right and its thermal death curve lies above those
drops from
15 minutes, it
temperatures tested; the typical assumption is that one can extrapolate the line to higher of most of the other pathogens. So by the time Salmonella is reduced to the 6.5D level,
Death curve at temperature T ref
100 million to
drops another 90%
10
temperatures, but it may not be valid to extrapolate to lower temperatures. If one line lies
At 10 T million
ref
= 58 ˚C / 136 ˚F,
from 10 million
most other pathogens will have been reduced to an even greater extent. Note, however,
60
10
D in
ref
= 15 7 minutes...
to one million
below another, that means the pathogen indicated by the lower line is more heat-sensitive. that some bacteria produce spores that are very heat-resistant.
At 60 ˚C / 140 ˚F,
10
D
10
10
1
ref
= 15 min
At 60 ˚C / 140 ˚F,
D
40
ref
= 15 min
10
10
Temperature (°F)
At T ref
= 65 ˚C / 149 ˚F,
1
D ref
= 36 seconds
D ref
0.1
120 130 140 150 160 170
24 h
20
At 60 ˚C / 140 ˚F,
12 h
D ref
= 15 minutes
At 70 ˚C / 158 ˚F, At 65 ˚C / 149 ˚F,
1
0.01 D
0 15 30 ref
= 56h
min
D
45
ref
= 10 min Salmonella spp.
0
0.1 1
At 70 ˚C / 158 ˚F, At 65 ˚C / 149 ˚F,
1
55 57 59 61 63 65 67 69
0 10 20 30 40 50
0 10 55 D ref
= 20 5 min 60 30D ref
= 10
Cooking
min6540 time (minutes) 7050
0 10 20 30 40 50
10,000
Temperature (˚C)
1
1
Campylobacter
0 10 Cooking 20 time (minutes) 30 40 50
0 10 Cooking 20 time temperature (minutes) 30 (˚C) 40 50
Cooking 1h time (minutes)
jejuni
Cooking time (minutes)
Cooking time (minutes)
The death curve becomes a straight line when
The
The
time
higher
D is
the
the
cooking
number
temperature,
of minutes needed
the faster
to reduce
As the actual data points from scientific studies show below, thermal
1,000
Bacteria bacteria die counts at an are exponential expressed rate; as powers the curve of 10shows the number
the
bacteria
bacteria
die,
count
and the
to one-tenth
shorter the
the
D
starting
time
number (by 90%)
death curves vary from one 10 min kind of pathogen and food to another
The time D is the number of minutes needed to reduce
100 remaining alive over time.
100
A As graph the actual of D vs data temperature points from reveals scientific how studies long you show must below, hold thermal food at
100
Temperature (˚F)
100 the bacteria count to one-tenth the starting number (by 90%)
a death given curves temperature vary from to achieve one kind a of tenfold pathogen (1D) reduction and food to in another bacteria
131 134.6 138.2 141.8 145.4 149 152.6 156.2˚F
100
Temperature (˚F)
100
131 When 134.6 cooked 131 138.2 141.8 140145.4 149 149 152.6 156.2˚F 158˚F
100
100 at 60˚C, the
1 min
80 When cooked
bacteria count
...and in the next
at 60˚C, the
drops from
15 minutes, it
30 s
bacteria count
Death curve at temperature
...and
T
in the next
100 million to
drops another 90%
ref
10
drops from
15 minutes, it
10 million
At 60 from ˚C / 10140 million ˚F,
100 million to
drops another 90%
10 in 15 minutes...
At T ref
= 58 ˚C /
D
136
ref
= 15 to ˚F,
10 s
min one million
10
60
10 10 million
from 10 million
in 15 minutes...
to one million
10 10
D ref
= 7 minutes
Trichinella spiralis
1
10
E. coli
1
40
1s
1
At T ref
= 65 ˚C / 149 ˚F,
D ref
D ref
= 36 seconds
0.1
ns)
Time
0.1 s
0.01
55 57 59 61 50 63 65 67 55 69 60 65 70 75 80
Temperature (˚C)
Temperature (°C)
MICROBIOLOGY FOR COOKS 151
0.1
Time (seconds)
2