A widely used method for heat sterilization sometimes called a steam sterilizer. Autoclaves use steam heated to 121-134 °C under pressure. To achieve sterility, the article is heated in a chamber by inject steam until the article reaches a time and temperature set point. The article is then held at that set point for a period of time which varies depending on the present on the article being sterilized and its resistance to steam sterilization. A general cycle is 20 minutes at 121 °C at15kPa, which is sufficient to provide a unfruitfulness assurance level of 10−4 for a product with a of 106 and of 2.0 minute .Following sterilization, liquids in a pressurized
Biological indicators can also be used to independently confirm autoclave performance. Simple bio indicator devices are commercially available based on microbial spores. Most contain spores of the heat resistant microbe Geobacillus stearothermophilus which is extremely resistant to steam sterilization. Biological indicators may take the form of glass vials of spores and liquid media, or as spores on strips of paper inside envelopes. These indicators are placed in locations where it is difficult for steam to reach to verify that steam is penetrating there.
For autoclaving, cleaning is critical. Extraneous biological matter or grime may shield organisms from steam penetration. Proper cleaning can be achieved through physical scrubbing, or pulsed similar to autoclaving, and when performed correctly renders food sterile.
Moist heat causes destruction of micro-organisms by denaturation of macro organism
Dry heat sterilization
Incineration is a waste treatment process that involves the combustion of organic substances contained in waste materials. This method also burns any organism to ash. It is used to sterilize medical and other bio hazardous waste before it is discarded with non-hazardous waste. Bacteria incinerators are mini furnaces used to incinerate and kill off any micro organisms that may be on an inoculating loop or wire.
it is an outdated and lengthy process designed to reduce the level of activity of sporulating bacteria that are left by a simple boiling water method. The process involves boiling for a period at atmospheric pressure, cooling, incubate for a day, then repeating the process a total of three to four times. The incubation periods are to allow heat-resistant spores surviving the previous boiling period to germinate to form the heat-sensitive vegetative which can be killed by the next boiling step. This is effective because many spores are stimulated to grow by the heat shock. The procedure only works for media that can support bacterial growth, and will not sterilize non-nutritive substrates like water.

Dry heat was the first method of sterilization, and is a longer process than moist heat sterilization. The destruction of microorganisms through the use of dry heat is a gradual phenomenon. With longer exposure to lethal temperatures, the number of killed microorganisms increases. Forced airing of hot air can be used to increase the rate at which heat is transferred to an organism and reduce the temperature and amount of time needed to achieve sterility. At higher temperatures, shorter exposure times are required to kill organisms. This can reduce heat-induced damage to food products
The standard setting for a hot air oven is at least two hours at 160 °C. A rapid method heats air to 190 °C for 6 minutes for unwrapped objects and 12 minutes for wrapped objects. Dry heat has the advantage that it can be used on powders and other heat-stable items that are adversely affected by steam.

Author: Mahesh Kumar Sharma