I want to know how the tuna can be kept for so long in a can. Do they use preservatives? Or is it just tuna and water (or oil or brine)?

  • If you can't define what you do and don't want, it's usually best to just not ask about it. Ask what's in canned tuna besides tuna and water (or oil or brine) and then you can figure out if you like it or not. (removed discussion of natural/artificial stuff - it's a recurring topic here and we don't need it rehashed every time)
    – Cascabel
    Feb 25 '16 at 12:25

The preserving effect of canning is based on

  • removing all bacteria and fungi (normally present at least to some extent even in perfectly safe food) by a combination of heat and pressure over a certain time
  • preventing new bacteria or fungi from reaching the food by sealing the containers
  • avoiding oxidation by sealing the cans
  • sometimes supporting this by ingredients that are very inhospital for bacteria and fungi like acids (pickles, anyone?) or sugar (less available water).

For your tuna, this means the heat/pressure of the canning process is sufficient to prevent spoilage for a long time.

Special preservatives are typically not necessary. Checking the label should confirm this. If one brand should have choosen to add them nonetheless, you can pick another manufacturer.

  • Perfect answer, though I would start with "No chemical preservatives, but tuna is preserved in the following way..." Or something like that.
    – Escoce
    Feb 24 '16 at 15:27
  • 3
    @Escoce, NaCl counts as "chemical" for you? Feb 25 '16 at 7:30
  • That's like asking "How about H2O?" Everything is and is made of chemicals. The omega-3 acids are chemicals too. Besides salt is not required for preservation in this case, it's a flavor enhancer so that canned tuna isn't as bland as it normally would be.
    – Escoce
    Feb 25 '16 at 16:19

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