- The basic frozen foods -- vegetables, fruit, fish and meat -- are normally free from added salt and sugar. Frozen meat and poultry can have added water, and polyphosphates (which help to retain the water until you cook the food).
- Make sure that frozen meat (particularly poultry) is completely thawed before you start cooking it. The danger is that you'll start cooking with the centre of the joint or poultry still frozen. The outside will be cooked, but the inside will be an incubator for bacteria.
- Don't re-freeze food which has been frozen and then thawed. The thawing will have increased the bacteria in the food, and when it's thawed again you'll get a second multiplication of bacteria -- possibly dangerous.
- Don't keep thawed food -- especially poultry -- for long periods in the fridge. The highly toxic organism listeria can go on multiplying at temperatures right down to freezing point.
- Dried foods can have additives: watch out for them. Dried fruit may be coated in mineral oils -- potentially toxic preservatives. They may also contain added sulphites, which can cause asthma attacks, headaches and nausea.
Some tins have a no preservatives label -- but there's nothing remarkable about that. Canning meats often have a chemical preservative (nitrite) which is now controversial, because of a possible link to cancer in animals.
Other things to look out for are added flavourings, colourings, and added salt and sugar. Some cans have a breakdown of the proportions of fat, sugar, and salt.
- Don't buy a can if it's dented. The internal lacquer inside the can may have been damaged, and particles from the tin may have dissolved into the food.
- Look out for rusting, faulty seams or swollen ends. If the can is swollen it is possible that gas has been produced inside it. This is caused by insufficient sterilisation, and can provide conditions favourable for the growth of the bacteria clostridium botulensis (a cause of the toxic food poisoning botulism).
- After opening the can, any remaining contents should be stored and handled as fresh food. Make sure the leftover contents are properly reheated before eating.
- Store cans in a cool place. During storage there is sometimes a slow chemical deterioration of the product, depending on storage temperatures, residual oxygen, and the surface type of the can.