There are many methods that used for Food preservation and extend shelf life. Low acid and acidified packaged products are applied heat by heating media to cook and kill a target microorganisms. Then these products can be kept for long shelf life under non refrigeration.

Thermally process packaged food can be divided in 2 groups as low acid and acid/acidified food. pH and water activity are a factors that use for consider a product group as following.
- Low acid food (LAF) is a food contains pH greater than 4.6 and water activity (aw) above 0.85. The product must be processed by application of heat to achieve a commercial sterility. The temperature of processing should be in range of 116-125 °C. The target microorganism is Clostridium botulinum type A and B. The process determination is considered from sterilizing value as F0. Generally, minimum F0 is 3 minutes but normal production is normal 5-8 minutes.

- Acid/Acidified food is food that contains pH equal or below 4.6 and water activity above 0.85. The product can be used pasteurization level for heat application. The target microorganisms are spoilage group. The application of heat is depended on pH of product.

- Low acid water activity controlled product, the product that contains water activity is greater than 0.85 and lower than 0.93. Because of aw less than 0.93 can inhibit the growth of C. botulinum.
- High acid food is a food that contains pH lower than 3.5. This product can be produced by hot fill and hold process. 
Examples of work SRA Tech steam water spray retort
Working step in SRA Tech steam water spray retort
Fill water into retort as specifred level. The water level is controlled by PLC to prevent low flow of water and flood the bottom product stacked in bottom layer.
Pre-heating system (if set) will automatically run to set point to maintain the initial product temperature and reduce come up time period affect to short cycle production time. Then the PLC will run to Come up step to bring up the temperatuer to processing period with direct steam inside.
Cooking period, The PLC maintains the temperatuer, pessure, flow rate and water level as setting. lt will be alarm once the critical parameter deviated such as low temperature, low pressure, low flow.
PLC will alarm when changes the period of working (cooking, cooling). The products were cold by indirect cooing system with plate heat exchanger that no need to use chlorinated water.