THIS IS ABSOLUTE AND ALSO DANGEROUS
When we make preserves to the Water bath we boil the product inside a closed boat with which we do not do other thing than to sterilize it. This sterilization is what will allow us to store the pot in the pantry for long months without risk of contamination.
When we do vacuum packaging with the packaging machine we do not sterilize the contents of the can, all we do is extract the air with oxygen. With this we achieve that the product has a longer duration and that it retains its flavor and texture for longer but never for months. In addition, the jar vacuum packed by this method should be stored in the refrigerator at less than 5 º C and its approximate duration will be 2.5 to 3 times what would have lasted inside a jar without being vacuum packed.
The conservation of cans made by vacuum packaging without sterilization is very dangerous because the absence of oxygen is the ideal place for the development of Clostridium botulinum bacteria that produces the very dangerous poisoning called botulism.
This bacterium can not develop when the food is stored in the refrigerator at a temperature below 5 ° C or frozen.
The people are armed then a mess and tells us that when doing the bath Maria preserves is packaged vacuum.
Indeed, this is true. By heating the water and begin to boil inside the jar the volume of the food expands and expels the air out of the jar. When the jar begins to cool the food contracts to its natural volume and when there is no air, there is an empty space inside the jar. The external pressure pushes the lid of the jar inwards and is what makes it sealed and the jar vacuum packed but we have also sterilized (by boiling) so that there is no risk (if done correctly) of that the bacteria that could produce botulism develop.