 In this module, we will talk about sterilization in detail, but before talking in detail about sterilization, we should know first what is contamination. Contamination is the invasion or the introduction of unwanted microorganism into a specific area or into a specific object, especially when we talk about with the fermentation process into the fermentation vessel. So, if the contamination is the invasion of unwanted microorganism into the fermentation, then we said that that process is contaminated. So, the sterilization is a method just to avoid or just to prevent the fermentation process for unwanted microorganisms. Before talking in detail, so if there is a contamination, what will be the factors, what possible outcomes can be, as we know that the fermentation is a process by which we have the mass-culturing of the microorganisms for the sake of any desired product. So, the fermentation process is totally a process that only focused on a specific, either a single organism, either if there is a mixed fermentation, then two organisms can be, but if there is any invasion of any other microorganism, then there are some consequences in a result of contamination. So, what are those consequences, let us see what are those. First of all, if the medium which is the main part of the fermentation process would have to support the growth of both the production organism, which we called as specific organism and the contaminants resulting the loss of productivity, because there will be a competition to require different nutrients. So, that is the first possibility if there will be a contamination. But in second consequence, so if the fermentation process is contaminated, especially when there is a continuous process, then the outgrowth happen of the contaminant, which slowly and slowly with the passage of time that will displace our specific organism, which we called as production organism. So the loss of or the displacement of the specific microorganism with the contaminants. As concerned, the third possibility that the foreign organism may contaminate our final product because when there will be a contaminant in that, that will grow, that also excrete, that also produce some unwanted product and that can mix with our desired product. So the other consequences that may happen that is the contamination of our desired product because in case of single cell protein production, if we are only considering only with one microorganism, if there is an invasion of another microorganism, then our protein will be contaminated. So as concerned the fourth consequence, the contamination may produce some compounds, which make problem while extracting our desired product. So that the contamination can lead to the difficulties and the complexities in our down streaming process. So as concerned, the fifth consequence that the contaminants may degrade our desired product because each and every organism has its own need and have their own excretions, especially you can see in this that some when we are dealing with some antibiotic productions. So when we are dealing with the beta-lactamase antibiotics and if there is a contamination of those microorganisms, which are having the beta-lactamase producing, so that can degrade our such antibiotics. So on other hand, if there is some microorganism and we are dealing with the enzyme production, then the contaminants can produce such proteases, which can hydrolyze our desired enzymatic proteins. So as concerned the sixth consequence, the contamination of the bacterial fermentation with phage could result in the lysis of the bacterial culture. So these are the six different consequences that can happen in a result of contamination. So in all cases, we can say we have to avoid the contamination and then there is only one possible way that is the sterilization. So by the sterilization, we can have our desired fermentation process. So what is sterilization? Sterilization is actually the removal or the destruction of the living microorganisms from the desired object. So in fermentation process, there are different objects. Number one, that is the medium. Second is the fermentation vessel. And third is the air, which has to be aerated into the fermentation vessel. And the fourth is all the lines, which we can call as sump and dump lines. So all these system and all these require the sterilization process. So sterilization can be achieved by different number of ways in which heating is the most common method that is mostly used for killing the microorganism. But that has also very limitation, which will talk about those limitation in next modules. So thus, as concern, the agent which is used for the sterilization that is known as sterilant, that can be a liquid, that can be a heat, that can be any gas, that actually give us the removal or the destruction of any living organisms. Even sometimes the filters, especially in case of the air filtration, air sterilization, air filters are used for sterilization purpose.