 In this module we will talk about the medium sterilization, but in detail we will try to discuss the calculation of the del factor during heating and the cooling. As we know that the overall sterilization process is depend upon the viable number of cells, but actually when we talk about the stabilization of the medium, we have to take this process by dealing with the heat stabilization process. So, as we see in our previous module that the overall del factor include the del factor of heating, cooling and the holding time. So, let us try to see in detail that how we can calculate the del factor. So, as we have seen in our previous modules that the relationship of the temperature we can see in this equation that the del factor is equal to A which is the Arrhenius constant and T and E and then minus E over R T. So, this equation actually shows the relationship of the del factor with the temperature and the time. So, this T is the time. So, however during the heating and the cooling period the temperature is not constant because when the process of sterilization start temperature gradually increase. So, when there is a required temperature of the sterilization requirement then there is a holding time. So, the increment in the temperature with respect to the time then actually what happen that also effect on the del factor. So, that is we have to need to calculate the del factor on each integration of the above equation. So, as you can see in this slide that reported by the Indover and Humphrey in 1959 produced the integrated form of this equation for a variety of temperature to time profile including the linear exponential and hyperbolic. So, however the regime observed in this practice is frequently difficult to classify and then making the application of these complex equation problematical. Richard in 1968 demonstrate the use of graphical method to illustrate this relationship. You can see this relationship in the next slide. So, in this relationship we can see that how the time axis is divided into different increment according to T 1, T 2 and T 3 and so on. So, Richard basically suggest that 30 different reasonable number to increase the temperature. So, as concern you can see in this slide that on y axis is a temperature on x axis is a time. So, in first step so, this one and this two T 2, T 3, T 4, T 5, T 6 and so on. So, this is basically the graphical integration method that applied to the increase of the temperature. So, with the passes of the time temperature is gradually increase. So, if all these intervals which Richard said that that maximum should be the 30 which is the suitable number. So, then we can say that for each increment the temperature corresponding to the midpoint time is recorded. It may now be approximated that the total del factor of the heating up period is equivalent to the sum of the del factor of the midpoint temperature for each time of the increment. So, the value of the specific death rate in case of bacillus stereothermophilus spores as we have seen in our previous module. We are taking the example of the del factor of bacillus stereothermophilus spores. So, in this case then bacillus stereothermophilus spores at each midpoint temperature may be deduced from the Arrhenius equation using the thermal death characteristics as published by D. Inrofer and Humphrey in 1959. So, the value of the del factor corresponding to the each time increment may then be calculated from this equations. So, as concerned in the first increment del factor 1 that is equal to k 1 and t del 2 k 2 over and t and same on in each increment we can calculate the del factor of each step. So, the sum of the del factors for all the increments will then equal the del factor for heating up the period. So, with the same pattern when we are dealing with the del factor in the cooling pattern. So, the pattern will be the same. So, if we are talking about the heat up system and then the cooling system and then in between the two is the holding time. So, the del factor is basically the mixture and the addition of all the del factors include in the heating up system and the cooling down the system. So, in later module we will talk about in detail that how we can further elaborate this del factor.