Tinned or canned foods are an integral ingredient of any food production facility and, while tinned foods are generally considered to be fully sterile after production, there are several factors that can affect the safety of the foods in tins.
The structure of a tin is designed such that the foods held inside are fully separated from the outside environment in all ways, such that there is no opening of any kind from the outside of the tin to the inside.
Through the canning process tins are fully sealed, usually using a double seam seal between the lid and the body of the can or tin.
The contents inside the canned foods are in an environment that is under a constant vacuum and anaerobic (no oxygen) conditions.
The insides of the can body and lids are lined with an inert layer, mostly a plastic lacquer layer, to keep the contents separate from the metal that the tin is made of.
Depending on various chemical characteristics of the food product, the foods are heated at different temperatures to obtain full sterility (no living bacteria at all). The heating is normally done in pressurised vessels, filled with water, called autoclaves so as to obtain heating temperatures above 100°C. Most foods are heated to above 121°C to ensure all bacteria are killed regardless of what growth or survival phase they may be in.
All of these production parameters result in tinned foods being highly shelf stable for extended periods of time and thus make tins an excellent means of storing bulk foods without the need for refrigeration.
HOWEVER, if any one of these parameters is not met during production or are compromised after production then the integrity of the tin and thus the food inside is also compromised.
When receiving and storing tinned foods the following needs to be monitored to avoid unsafe foods being used in the food production facility:
- Rusted or dented tins
- The rust and dents compromise the structural integrity of the internal inert layer, thus rustling in metal ion leeching into the foods which can have a chemical toxicity effect and can make the foods have a poor taste.
- Severe rust and dents can cause pin-holing or ruptures in the tin body or seam which will release the vacuum inside the tin and allow oxygen, liquid and microbe ingress into the food in the tin.
- If tins arrive at the facility dented or rusted, they should be rejected upon receiving and sent back to the supplier.
- If tins are dented after they arrive in your facility (dropped while packing them onto the dry store shelves for instance), they should be issued to the production operation, opened and the contents decanted into a sealable container immediately. The foods should then be treated as normal prepared foods.
- Foods should never be stored in their original tins once opened, not even in a fridge. They should be decanted into a sealable container.
- The same problem as above, of ion or chemical leeching, may easily occur once the tin has been opened and the raw edge is exposed to the foods.
- Opened tins are often difficult to store fully covered.
Expired tinned foods
- While the unofficial and potentially misguided consensus may be that tinned food can be kept and used beyond its expiry date, it is not a good idea at all to do so.
- The manufacturers of tinned products put the expiry dates on the products for a reason and as the experts on their own products, we should follow their guidance.
- Rotate tinned food according to expiry dates so as to use the older foods first.
- Do not receive food that is past, or close to being past, its expiry date.