Should humanity face a nuclear apocalypse of worldwide war, we need to understand which foods might be safe for survivors to eat, and how long the foods will last.

To understand this, we need to ask what makes food spoil.

Most foods spoil because of the growth of microbes. Preserving food is an attempt to limit microbial growth. Food can be preserved by drying, salting, chilling, or storing in air-tight containers.

• Drying is the most effective because microbial growth is inhibited.
• Salting...

Preservatives are used in foods to extend their shelf lives. One of McDonald's Big Mac in Iceland is an example of a long-lasting processed food. It has been on display since 2009, in a glass box. Preservatives that has been discontinued by McDonald's are:

• calcium propionate that pre...

• Twinkies will last no longer than similar treats. One Twinkie has been kept in a time capsule for up to 44 years.
• Honey is almost impossible to spoil because it is high in sugar and low in water. Some honey samples are 3,000 years old.
• Very fat-rich foods like butter an...

• Unless a nuclear or chemical incident has contaminated the food, all foods that are not in the fresh aisle can be eaten with confidence. That is tinned or dried foods and even frozen foods. Vacuum packed would also be useful.
• Slow-dried food could still harbor microbes. Spray-dri...