The Irish have their traditional potato dishes. The Italians have their traditional tomato-based pasta sauces. There are also the traditional cuisines of Malawi and Thailand that make use of peanuts.
So, how old, on average, is traditional cuisine? Is there any research on how long it takes for a new dish or ingredient to integrate itself into a culture’s cuisine to the point it’s considered traditional?
110 years max, realistically 80 years.
Remember, up until a couple of hundred years ago most people were illiterate, and what little written material that was available to the public was not books of recipes.
So the traditional diet was whatever people could remember eating all their lives. As soon as the oldest people who grew up on another diet died, the new diet became traditional.
This reflects a rather surface understanding of tradition. It isn’t passed on from individual to individual, but individuals within a larger group to other individuals within the same larger group. When grandma dies, her kids still remember how she used to make it.
Further, there is invariably variation within the cuisine (recipes & preparation differ slightly, etc.) Aunt Ursula made it different from grandma. Finally, no tradition is static, so what happens in all cultures is gradual change over time. Grandma used to cook with butter when she was young. Then she switched to margarine. Finally, she stopped making that recipe altogether.
Some cultures change faster than others, largely depending on how much contact they have (more new ideas = more likely to change) and resources. So first the OP has to define how much change is allowable before a tradition counts as “changed.” If it has to be static, the answer is pretty easy: a point in time. If you want, “how long before it is recognizably different,” I’d say less than an individual lifetime in today’s world. The study of traditional foods is called “foodways” and it’s a fairly recent area of study, so there’s isn’t anything in the way of hard-core cross-cultural longitudinal data. Anecdotally, though, while certain basic dishes and flavour combinations last a long time, traditional cuisine itself is pretty flexible.
Well, for the two cuisines mentioned byt the OP, not more than 500 years. Both the tomato and the potato are native to the New World, so neither Ireland’s potato dishes nor Italy’s tomato dishes existed before those two plants were brought back to Europe.
Wiki article on tomatoes:
Wiki article on potatoes:
Peanuts are also originally from the New World. They were imported into Asia by the 1600s. Given the fact that Portugal had colonies in both Brazil and West Africa, they probably reached Africa before then.
Chilis, used in Indian, Thai, African, and many other cuisines, are also of American origin.
I assume that the OP already knew that those were new-world vegetables, and that that’s what prompted the question.
Corn also. I do wonder how long it took. ‘‘Well my mother never cooked tomatoes, potatoes, corn, or peanuts.’’
I would argue that people consider something “traditional” if it’s been around all their life. I think many Americans consider the green bean casserole to be traditional, and that was only invented in 1955.
True, but American corn doesn’t really seem to have caught on in the rest of the world the same way that potatoes or chilis have. You’ll see it occasionally, but I can’t think of any “traditional” Old World dishes that are based on corn.
Polenta is generally corn-based, although I’ve read that it’s occasionally made with chestnut flour. Apparently, back in the pre-corn days it was made with barley.
So how does any of this contradict what I said.
When the oldest person who who can remember not eating a food dies, then a new tradition has emerged. It makes no difference whether the survivors don’t remember the new food being made by Aunt Ursula or they don’t remember it being made by Grandma. If they don’t remember it being made then the tradition is dead.
Ditto for the idea that recipes vary regionally. Of course they do. Thai food still varies regionally, nonetheless peanuts are an intrinsic part of traditional food cuisine.
Thank you. 
Yes. That’s why I specifically singled all of them out. Apparently, the (resumed) contact with the New World hit a number of Old World cuisines like a hammer. Or, at least in the case of potatoes and tomatoes, like an invasion by a band of shady zombies. 
Anyway, there are some good responses in this thread. I thought it might be a bit longer than 80-110 years, but the arguments seem to make sense at any rate. scr4’s post is very interesting on that front.
You said
But the new diet becomes traditional as soon as it’s adopted into the tradition. It has nothing to do with memory. You can be aware of an earlier iteration of your traditional cuisine. Tradition doesn’t mean “only the oldest things we know about.” It simply means that there is continuity over time. Nor is tradition limited to the uneducated. I imagine quite a number of Thais are aware that peanuts and chilis are non-native.
It’s my personal theory that when some dish is called part of the traditional cuisine of some region or country, it means that it was a standard food item there between 1900 and 1950. Some dish that was standard in 1450 (but which disappeared from their menus before 1900) is not considered part of the traditional cuisine of that region or country. Any ordinary cook (as opposed to a food historian) would never have even heard of the item. It’s just a forgotten piece of history. Any food item that has become standard in that region or country’s cuisine since 1950 is nouvelle cuisine for that region or country. I disagree that green bean casserole is a traditional item (in the U.S.) as yet. There are people living who remember when it was introduced.
Though to be honest, in chinese cuisine the chili slipped into dishes that were already rendered ‘hot’ by other spices-if you like in Paul Buell’s Soup for the Qan, there are a number of dishes that are very pungent. BalPo soup is a good example, mutton, mutton broth, chick pea, radish [daikon] and the heat provided by black cardamom, black pepper, asfoetida and vinegar. It uses corriander leaves as garnish. Interestingly enough, the recipe is still made today.
[I love a recipe that can be *directly* traced back to the origin in an actual published cookbook from the 1300s!]
Maybe ‘traditional’ is ‘pre-industrial’?
It’s all a question of definition. In the Middle Ages, 1000 years ago, or in the Stone Age, 10 000 years ago, people ate grain gruel/ stew. When the potato arrived, it was added as part of the stew, along with spices from the spice islands. Does this count as traditional recipe or a new one?
Likewise, while the Italians invented the Pizza Margharita for their new Queen rather late, and the currently traditional Italian pizza is with Tomato sauce, the idea of a flat bread with stuff on top can be found in many cuisines. The Turkish imbiss places call their Lamacun Turkish pizza so people know what it is.
And while Spaghetti with tomato sauce had to wait for Columbus, Spaghetti with other sauces like Alio e Olio (garlic and oil) were traditional before, since legend has it that Marco Polo brought the noodles from China to Italy. (Since it’s doubtful he went all the way, or rather, just travelled part of the silk road and listened to stories from other relays, him bringing back noodle recipes is also a bit doubtful).
On the other hand, traditions can form and spread quickly. In the 50s and 60s,Currywurst was a new street food in Germany. But in the 90s, it was overtaken by the rising star of popularity, the Döner Kebap (from the many Turkish eateries).
The new trend in the last 10 years (besides the rise of Sushi everywhere) is Wraps - they came over from America, and now everything is being wrapped, even things that were never wrapped before.
What he said. Spaniards are aware that fideuá was invented thereabouts of the 1950s - yet try and pry it out of our “traditional recipes” books. It’s an iteration on fish paella, itself one of the many varieties of paella (according to legend, fideuá is what a fishing boat’s cook came up one day that he ran out of rice/ discovered that the rice had been ruined: he simply used noodles instead of rice). Fideuá sort of inherited the traditionality of fish paella, while providing yet another variation on the same theme. There are restaurants in an around Valencia which cook nothing but varieties of paella: they do not have any pastas. No. Nope. Well, except fideuá, which “as anybody knows” is a variation on paella and therefore “counts” for purposes of having a paella-only restaurant.
Another clarification would be what exactly you mean by “traditional.” Are hot dogs and hamburgers “traditional” American food, even though they have German roots? How about the American version of pizza, which has been around for more than 50 years? I think most people still consider pizza “Italian” food, while few think of hot dogs and hamburgers as “German” food.