Canned tuna is truly a wonder of the modern age. If you have ever heard of certain foods, such as Twinkies, being able to survive nuclear Armageddon, then you might begin to have an idea of the chemical wonders inside canned tuna.
So, how long can tuna last in the fridge?
Canned tuna can last indefinitely in the fridge for as long as it is not opened. Once canned tuna is opened, however, it should be eaten within a day. This is because tuna can only last about two days before spoiling in the fridge. If a food can only last one day or indefinitely, something is odd about it.
Clearly, there is a world of difference between canned tuna and normal tuna fish. Here are some of the reasons why these seemingly similar foods have such drastically different lifespans.
Packaging And Sealing
The first and most obvious difference is in the way normal tuna and canned tuna are packaged. This makes more of a difference than you might think, and it has to do with the way bacteria and vacuum seals work.
You see, bacteria are everywhere. They are in the air, on most surfaces, and growing inside most foods. This is cause for alarm as far as most people are concerned, but it need not be. An overwhelming number of bacteria are harmless. In fact, many bacteria are helpful to your body.
Human bodies are strange in that they rely on bacteria they themselves cannot produce in order to survive. Many animals, including tuna, feature this same quirk of biology. This can be a problem, as it creates a situation where the bacterium inside the tuna outlives the tuna that hosts it and continues to grow inside it.
This bacterium will often not be as friendly to humans as it is to tuna. Luckily, humans solve this problem by cooking the tuna, or eating it before that bacterium can grow to an amount that is harmful to humans.
But what if you could extract that bacterium from tuna altogether? What would happen then? Well, such a thing has been done, and it is one of the main reasons why canned tuna can last for so long.
Canned tuna is vacuum sealed. What does this mean? It means that not only is all the bacteria inside the tuna removed, but all the empty space is as well. Well, not all of the empty space. The universe is still 99% empty space, and no vacuum created by humans will change that.
But the point is, there is nothing inside a can of tuna besides the can and the tuna itself.
Preservatives, Preservatives, And More Preservatives
This makes it sound like there is a veritable cocktail of preservatives in canned tuna. The reality is much more straightforward though, as canned tuna contains basically only one preservative: Nitrates.
It is so common for preservatives to be overly busy tongue twisters like “high fructose corn syrup” that the simple name “nitrates” almost sounds menacing. Nitrates are a toxin for lower lifeforms like, you guessed it, bacteria. This is what canned tuna soaks in to create an environment that is inhospitable for bacteria.
Nitrates can also kill humans too in great enough quantity. The amount of nitrates it would take is rather large, but it is actually surprisingly possible as well. The United States Department of Agriculture actually recommends you eat less than twelve ounces of skipjack canned tuna per week to avoid nitrate poisoning.
For denser tunas, the recommended amount is actually less than four ounces per week. This can be a bit alarming when you see skipjack sells tuna five ounces at a time, but remember: Skipjack is safe up to twelve ounces, everything denser than that is safe up to four ounces.
Tuna, Mayo, And You
The last point on the preservation of tuna is how it interacts with mayonnaise. Mayo can have the interesting effect of elongating tuna’s lifespan by a whole day in the fridge. This might not seem significant, but the fact that mayo is so rich with preservatives and fats that it can extend the life of a meat in the fridge is surprising.
Do not take this as an utter condemnation of mayo, however. It is something a new person learns every day: Fat is not inherently unhealthy. Fat by way of sugar is unhealthy because your body does not know how to burn it. Fat by way of animal fat and butter is fine.
This is because fat by animal fat and butter is far easier for your body to digest. Mayo is basically straight fat, and while in excess that can do all sorts of terrible things to your body, you usually do not need much mayo to get the taste you want. The fact that it can help preserve things is just a plus.