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.)

        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.

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