Preserving

­Because food is so important to us, food preservation is one of the oldest technologies used. I­n certain cases, a preservation technique may also destroy enzymes naturally found in a food that cause it to spoil or discolor quickly. An enzyme is a protein that acts as a catalyst for a chemical reaction, and enzymes are fragile. By increasing the temperature of food to about 150 degrees Fahrenheit (66 degrees Celsius), enzymes are destroyed. A food that is sterile contains no bacteria. Unless sterilized and sealed, all food contains bacteria. Bacteria naturally living in milk will spoil the milk in two or three hours if the milk is left out on the kitchen counter at room temperature. By putting the milk in the refrigerator you can't get rid of the bacteria that is already there, but you do slow down the bacteria enough that the milk will stay fresh for a week or two. Milk is a big example since it spoils fast but their is always a way that we can slow the process. Fruits a big thing to we learned how to pickle and jar it up to make it last longer we have been doing this as long as we have been eating.

http://science.howstuffworks.com/innovation/edible-innovations/food-preservation.htm