Is canned foods are good to eat ?

In canning and bottling, the key ingredient is the container itself. Sterilized and airtight vessel seals out the germs that would make a meal of its contents. What's on the inside the deviled ham or lima beans  or bottled pickle remains inviolable, ready to eat for up to five years.

Initially, the contents undergo some form of preservation, usually cooking at high temperature; bacteria like extreme heat even less than they like cold. Sometimes, the canner adds acidic ingredients as preservatives.The prepared food is then sealed in the container, which is sterilized by heat- a blitzkrieg on remaining microorganisms. 

The temperature required for sterilization depends on the food.Traditional home-canning recipes often are for high-acid pickled foods and fruity preserves that can be safely sterilized by simple boiling. 

But to kill off dangerous germs such as the bacteria that cause botulism, low-acid meats have to get very hot-in the range of 2 I 5°F .This requires cooking under pressure.

If canned goods spoil (and they rarely do), it's always because bacteria slipped into the food during preparation or canning.The live bacteria inside produce carbon dioxide as waste, which bloats the can in that telltale sign of spoilage.