CALCULATING THE TOTAL GROWTH OF BACTERIA IN COOKED FOOD
USING THE FDA CODE CONTROLS

O. Peter Snyder, Jr., Ph.D.
Hospitality Institute of Technology and Management

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        The FDA Food Code tells us that cooked food can be held at 41ºF for 7 days or at any temperature between 41 and 140ºF, if the time is limited to 4 hours.  This, of course, is scientifically wrong, because pathogen growth actually starts at about 29.3ºF and stops, for all practical purposes, at 125ºF.
        Using the well-established Radkowsky bacterial growth predication equation (Radkowsky, 1983), and setting 30ºF as the start point, 41ºF for 7 days as a second point, putting 4 hours at about 115ºF (because it fits the equation), and setting the upper growth limit at 125ºF, I calculated the equivalent growth times from 30 to 125ºF (Snyder, 1998).  Remember, the FDA does not refer to specific bacteria.  This is based on FDA code time-temperature controls.  The FDA has never cited a source for the numbers in the code.  It appears to be 10 generations of Listeria monocytogenes at 41ºF and 10 generations of Salmonella / Staphylococcus aureus at 115ºF.  (See Table 1.)

Table 1.  Maximum Holding Times at Specified Temperatures


°F 
°C 
1 Multiplication of Pathogens 
SAFETY LIMIT*
10 Multiplications of Pathogens
<30 
<-1.1 
Safe
Safe
30
-1.1
297.14 hours
123.8 days
35
1.7
46.34 hours
19.3 days
40
4.4
17.99 hours
7.5 days
41
5.0
15.55 hours
6.5 days
45
7.2
9.49 hours
4.0 days
50
10.0
5.85 hours
2.4 days
55
12.8
3.96 hours
1.7 days
60
15.6
2.86 hours
1.2 days
65
18.3
2.16 hours
21.6 hours
70
21.1
1.69 hours
16.9 hours
75
23.9
1.36 hours
13.6 hours
80
26.7
1.12 hours
11.2 hours
85
29.4
0.93 hour
9.3 hours
90
32.2
0.79 hour
7.9 hours
95
35.0
0.68 hour
6.8 hours
100
37.8
0.59 hou
5.9 hours
105
40.6
0.52 hour
5.2 hours
110
43.3
0.47 hour
4.7 hours
115
46.1
0.46 hour
4.6 hours
120
48.9
0.56 hour
5.6 hours
125
51.7
3.10 hours
31.0 hours

        Now, how does a foodservice operator use this?  I have developed a simple calculation sheet so that the operator can find the equivalent growth in a process between 30 and 125ºF.  First, the operator must collect times and temperatures for a process and put it in the blank table (Table 2).  Then, for each temperature, the operator looks up the growth / hour from Table 3, fills in this information on Table 2, and calculates the growth for each step in the process.  When the growth reaches 10 generations, the operator must have used up the food.  This is exactly equivalent to what the FDA allows with 41ºF for 7 days or 4 hours at 115ºF.

Table 2.  Calculation Worksheet


Description
 Temp. (F)
 Time(hr.)
Multiplication
rate / hr
Multiplication
Accumulated multiplication
           
           
           
           
           
 .

Table 3.  Calculated Rates at Specified Temperatures


Temp. (F)
Multiplication
rate / hr.
Temp. (F)
Multiplication
rate / hr
<30
Safe
82
0.965
30
0.003
83
1.000
35
0.022
84
1.036
40
0.056
85
1.073
41
0.064
86
1.110
42
0.074
87
1.148
43
0.084
88
1.186
44
0.094
89
1.225
45
0.105
90
1.265
46
0.117
91
1.305
47
0.130
92
1.346
48
0.143
93
1.387
49
0.157
94
1.429
50
0.171
95
1.472
51
0.186
96
1.515
52
0.202
97
1.558
53
0.218
98
1.602
54
0.235
99
1.647
55
0.252
100
1.692
56
0.271
101
1.737
57
0.289
102
1.782
58
0.309
103
1.827
59
0.329
104
1.872
60
0.350
105
1.917
61
0.371
106
1.961
62
0.393
107
2.004
63
0.416
108
2.045
64
0.439
109
2.083
65
0.463
110
2.119
66
0.487
111
2.149
67
0.512
112
2.174
68
0.538
113
2.190
69
0.565
114
2.196
70
0.592
115
2.188
71
0.619
116
2.163
72
0.648
117
2.115
73
0.676
118
2.038
74
0.706
119
1.927
75
0.736
120
1.775
76
0.767
121
1.573
77
0.798
122
1.319
78
0.831
123
1.013
79
0.863
124
0.668
80
0.897
125
0.323
81
0.931
126
0.058
   
>127.5
Safe

 
 

References:

  • Ratkowsky, D. A., R. K. Lowry, T. A. McMeekin, A. N. Stokes, and R. E. Chandler.  1983.  Model for bacterial culture growth rate throughout the entire biokinetic temperature range.  J. Bacteriol. 154(3):1222-1226.
  • Snyder, O.P.  1998.  Updated guidelines for use of time and temperature specifications for holding and storing food in retail food operations.  Dairy Food Environ. Sanit.  18(9):574-579.

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