By ALANA AL-HATLANI A stream of Park Slope families, girls with selfie sticks, and man buns with skateboards trickle into Prospect Park at 11a.m. on a Sunday—a congregation of urban foodies on their way to a fast-food ‘service.’ Everyone stakes their claim at a handful of benches or optimal shady patches of grass. Groups circle the booths before they open. They divide and conquer; cash in hand, splintering off to minimize wait time for raindrop cakes, ramen burgers, and something called a wowfull, at the weekend Smorgasburg food fair.

In 1986, it was molten chocolate cake, 1994 was the year of Starbucks, and in 2006 fro-yo was all the rage. While these foods haven’t expired quite yet, they’re pushing their sell-by date. As for 2017, each month seems to bring a new trendy food, from rainbow bagels to raw cookie dough. Tomorrow, it may be fennel pollen and jicama. Only Instagram and local farmers’ markets will tell.

Food trends aren’t new, but the number and ubiquity of them is, with trends exploding across social media, especially among millennials. Everyone’s a foodie today. But just as fast as these some of these trends appear, they disappear. Why does a food trend go from plate to trash-can?

“Like all death,” says David Sax, author of “Tastemakers: Why We’re Crazy for Cupcakes but Fed Up with Fondue,” “there is no one cause.”  Suspected causes include: oversaturation, death by social media, and replacement.

Oversaturation: Too much of a good thing.

Avocado toast, avocado roses, avocado fries, an entire restaurant devoted to avocados, the market is flooded with the green fruit, but that isn’t  necessarily a good thing for avocados. “​Once something is no longer novel, it’s often over,” says Eve Turow Paul, a millennial marketing expert. “Cool often is equated with special and unique. If something becomes super common, it can lose its ‘cool’ cache. ​”

With the sheer volume of food products on the market, it’s easy for consumers to move on. There are 15,000 new food products every year, and only 200 are still on shelf three years later, according to Phil Lampert, a Forbes columnist and food-marketing expert. Now that Silicon Valley is involved in developing new food products and launching them faster, like the meatless-plant burger, it no longer takes the standard three to four years, from development to sale, for a product to hit the market.

Social media also expedites the death of a food trend, with information at the touch of a button, the 15-minutes of fame is reduced to two.

Trend or Fad?  There is a key distinction.

“A fad is short lived, ideas in food that might pop up for a season, for maybe a few years, but peters out,” says Sax.

Dip n’ Dots, Jell-O salads, and fondue, can be classified as fads while trends reflect much broader changes in people’s eating habits. Japanese food, for example. “There is not a grocery store in the U.S. that doesn’t have a sushi counter,” says Sax.

Food trends tend to follow a rule of three: easy to acquire, replicable, and not too costly.

The Cupcake Case Study

It’s 9:45 a.m. and Georgetown Cupcake in Soho doesn’t open for another 15 minutes, but already a pair of twenty-something girls are knocking on the door. They know about the free cupcake of the day, studying Tweets for the secret flavor that earns them one of 100 treats.

By noon there is a steady line up Mercer Street and all the free chocolate salted caramel cupcakes are gone.  A trail of people leave with a shiny pink box decorated with a conspicuous black swirl sticker that much like the Starbucks siren lets the world know what’s inside without a peek: a $4 confection, a little bigger than a mandarin orange, with some elaborate configuration of fondant and frosting on top.

Cupcakes are relatively cheap, easy to make, and customizable, but are no accidental success story.  The infamous “Sex and the City” scene at Magnolia Bakery didn’t invent the cupcake trend. Sax sees other reasons, from nostalgia—cupcakes are among the first foods kids make with parents—to simplicity. Unlike the Cronut, cupcakes don’t require extensive pastry knowledge to replicate.

The right time and place also help. Sax believes that nostalgia was especially powerful when cupcakes first emerged in the early 2000s post 9/11 and then again when they reappeared in popular culture after the 2008 recession as they became comfort foods in difficult times, simple and reminiscent of childhood.

Trends, unlike fads, are connected to wider cultural phenomena. “Craft beer has a deeper culinary and political message behind it than just, locally sourced DIY hops or whatever,” says Sax.  Craft beer is a “narrative” that consumers buy because they care about the place, the family, and the techniques that create their beer.

Oh, and taste, that’s pretty important too, “People will try anything once, but they have to return to it, integrate, it in their life,” says Sax.

The McDonald’s Effect: A Fast Food Chain Starts Selling It

For a generation defined by experience rather than material goods, food is the perfect inexpensive adventure.  “They don’t have money and have high college debt, so they can’t go on a vacation, but they can go to Koreatown,” says Lampert.

Bragging rights enhance the experience. Food has always been marker of status. Caviar, lobster, and champagne all conjure a certain image and salary. Among millennials, Instagraming the limited-edition unicorn Frappuccino—within hours of release—is a way of showing off.  But once anyone can get a Cronut at Dunkin Donuts, there isn’t much to gloat about. In part, ubiquity sounds the death knell, but then so does the retailer, as traditional fast-food corporations are decidedly ‘uncool’ places to eat.

In a new world of fast food, just one out of five millennials have eaten a Big Mac, according to the Wall Street Journal, showing the brand’s waning popularity with the generation. From cage-free eggs to antibiotic free chicken, McDonald’s has tried to appeal to younger consumers, especially concerning food sources and health. Call it the Chipotle effect, but millennials want food fast with Slow Food sourcing ethics. McDonald’s can’t seem to make that work. The average customer is looking for breakfast all day, not quinoa salads.

Corporate doesn’t always fail. Starbucks, from their exposed-brick coffee shop aesthetic to their cold brew, has managed to stay on top of what smaller, hipper coffee shops do to keep millennials hooked. When chains can successfully sell food trends that only reinforces it. “When I can buy organic milk Walmart, the trend is established,” says Sax.

The Obituary: Traditional media proclaims its death

Year-end recaps happen for any sector, food included. Inevitably the lists emerge with trends that must “die.” In 2016, critics wanted everything from gold flakes to rainbow-colored food to go away. But their wishes were not granted because their wishes may not carry weight any more.

Social media has helped democratize critiques, with Yelp shifting the power of trend-makers into the hands of individuals and small businesses. Anthony Bourdain singing the praises of a restaurant on Twitter is perhaps better press than a stellar Pete Wells review. “Food critics and magazines are commentators today more than anything. Chefs, artists, entrepreneurs and everyday individuals are the trendsetters,” says Turow Paul.

The Replacement: Something better comes along.

Quinoa was replaced by more obscure ancient grains like farro and millet.  Hot lattes have been replaced by draft lattes that pour from a tap like beer.  Harissa is quickly becoming the new Sriracha.  It’s only a matter of time before something new comes along.

“Trends fade as they were usurped by competitors (those same fajitas and sushi platters giving way first to burritos and ramen soups and then to fish tacos and izakayas),”’ writes Sax in “Tastemakers.”

Millennial trend setting is being edged out by the emerging Gen Z. Food marketers are already studying their relationship with food finding, “a world of difference,” in comparison to their predecessors, according to Lampert.

While millennials are known for shopping online, he found that Gen Z likes shopping in store, 67 percent preferring brick and mortar to online. Like the “Silent Generation” of the 1950s, Gen Z is shaped by the 2008 recession and rise of global terrorism. They crave stability, with three-quarters wanting to own their own business.  They are generally frugal, don’t trust brand-names, hence Trader Joe’s tops their list of food retailers, and are even more socially conscious than millennials. They want to know how a product is made, where, and if it is made by people who share their same values, especially concerning the environment. Experts like Turow Paul predict they’ll make growing your own food trendy. Meaning soon, not just trees will be growing in Brooklyn.