Mainly there are two methods to kill harmful bacteria: physical methods and chemical methods. Today we will discuss physical methods in details. In physical methods: Boiling is the most common physical method which a common man generally practices. If we boil a product at 100 degree celcius for sufficient time all the harmful bacteria are killed. Drying the products like peas, spices, coriander, mint etc. in sun kills all the bacteria by making water unavailable for bacteria to thrive on. Making delicious, spicy pickles by putting lot of oil and salt is also a common man's method of food preservation. I am sure all of you must have come across the term pasteurized milk used extensively by milk vendors. Pasteurization is a process of raising the temperature for a short time and then cooling it quickly. It makes the milk safe to drink and kills all the disease causing bacteria. You must know that pasteurization and boiling are very different from each other, boiling can easily be accomplished in our homes but pasteurization is done in big industries only. Sterilization of packed disposable instruments like contact lenses and syringes is done with gamma radiation. Not everyone can use this process as it has to be done in a proper scientific setup and it is also very costly.