We had this for dinner tonight and it is amazing. Delicious, full of flavor, ofcourse everyone wanted the recipe.
My question is what is the purpose of purchasing tuna packed in oil when we drain it anyway? Just curious.
Canning (of virtually any food product) involves sealing the product in an airtight environment and heating it to kill micro-organisms, That's why canned goods last a long time. Thus, tuna canners need some liquid--oil or water--to displace the air in the can. Whether oil or water is a matter of personal preference, as each has unique effects on the tuna's flavor and texture. Think of canned tuna just like most other canned products: for example, canned peas need liquid for the canning process, but you drain it off before using the peas.
Oil packing is an old-timey method for preserving food and, in terms of fish, you will find this tradition was particularly strong along the Mediterranean coast. Packing in oil not only helped to preserve foods, but, since fat=flavor, the addition of fat to the preservation process resulted in a transformed product at the end. Nowadays, the concepts are so different, for example, many try to remove as much fat as possible from their foods and shy away from oil preserved foods in favor of those packed in water. When I think of oil packed tuna or other fish I always think of Mediterranean dishes and while you may drain most of the liquid away, some always remains behind. Mostly, I agree with davidpds above, the bottom line is that it is a matter of taste preference.
Personally I swear by oil packed tuna---particularly the stuff imported from Spain. It has a huge impact in flavor and the Gallician Spanish are experts at capturing that. It will cost you more (sometimes a lot more depending on the section of tuna) but it beats the hell out of Starkist.