Thank you for your reply. My concern was that the calculator uses the D value of 50.5 minutes at 61°C, with a Z value of 14 minutes. Researching the survival of Salmonella, I found that the time to reduce by 1 log was much short in similar media (peanut butter cookies, burger buns etc.). Though as you mentioned, the calculator operating on the T v t data would suggest I am not working to how the calculator was designed to be used given I am simply recording the core temperature at the end of cooking time. Also I was wondering about the 10 log reductions because the calculator outputs any lethality greater than 10 as simply being >10.
I downloaded the cookie app from site so I can see the source of yr data.
Do you know the core temperature at end of heating ?
As you know, the necessary time for a 1 log reduction depends on the D-value at the core temperature of the product during heating.
I anticipate yr measured core temperature at end of cooking is something like 80degC ? (assuming no cooling).
Just as an ideal example, assume the raw cookie enters at 20degC, is instantly heated to 80degC, remains at that temperature for "X" minutes, then is immediately cooled to 20degC.
The appropriate D-value for this process will then be D80 which is calculatable from the formula DT = D0 x (10^(T0-T)/z) using the data you previously quoted.
(z is assumed a constant)
This gives D80 = ca 2.49min
So time for a 1 log reduction at 80degC would be 2.49 min. and a 6D reduction (eg "X" above) would require ca 15 min
In practice the profile is probably like the picture attached below where lethality is probably occurring at (various) temperatures >= ca. 60degC so an integration of profile is required for a more accurate evaluation.
The above also assumes that all the batch is at same temperature which is unlikely. In practice, Need to find the slowest heating point.
cookie temp.profile.PNG 123.74KB
Does that answer yr query ?