Couple of reasons: The first one being oxidation. Oxidation is when matter loses electrons which are a major makeup of plant life. This the beginning of the breakdown of vegetable matter. Exposure to moisture from the air is also why vegetable matter will start to break down.
Reactions that spoil food need oxygen to occur
An airtight container keeps out fungal spores which is the main cause of mould.
If the food is non perishable, it can be left out if stored properly. Place the food in an airtight container. You can use a plastic storage bag for this too. Foods of this kind can last for a week or more.
Yoiu cannot really store perishable food for large amounts of time but to longer it life ther are a few steps that can be taken. 1. Airtight. Perishble goods perish due to contact with oxygen. Kepp it in an airtight container. 2. Light encourages perishability so keep it somewhere dark and cool.
The foods should always be stored in a plastic container. it should not be stored in any metal container as it gets corroded by acids present in the food and thus makes it toxic which act as poison in our body.
By using proper processing methods, canning provides for long term storage of foods without refrigeration. Cans don't break like glass and protect the food from oxidation due to exposure by light. It is portable and protects the food well under adverse conditions. The main problems are underprocessing, seam failure, dents and rust. In the United States, it is a highly regulated industry.
Seal the food in an airtight container or with freezer wrap and place it in the freezer. The best temperatures for long-term freezing of foods is between 0 degrees F to -18 degrees F, depending on the length you plan to leave the food in the freezer.
25lb of Dry Pet food See this link for a good example: http://www.amazon.com/Iris-Airtight-30-Quart-Pet-Food-Container/dp/B00024JPXW That would depend on the food. Dry foods weigh much less than wet foods and even among dry foods there is a large range in density.
Follow the directions on the clearer container. Keep them stored well away from any foods or food preparation areas.
Once opened, canned foods should not be stored in the can - even if refrigerated. Store the unused soup in a clean container, then seal and refrigerate. Use it within a day or two.
So the food can be stored away for a longer period of time without it going off.
Sous vide products are stored refrigerated - under 40°F. you also need to package the product in a suitable container to prevent the contamination of other foods, contamination will meen that bacteria will spread to other foods.
For long term storage, foods must be packed in a container that has minimum moisture and oxygen content, so the box should be airtight and leak-proof. Stainless steel food containers or glass food containers are probably the best options, since plastic can leak harmful chemicals into the food if stored for too long.