What’s pumpkin spice flavor, and why do we fall for it every autumn?

Stand down, cider: The pumpkin spice latte is the official beverage of fall. At least, that’s what a barrage of advertising and artfully composed Instagram photos would have Americans believe.

Like the zombie of so many B-grade horror flicks, every Halloween season the sweet, spicy beverage arises from Starbucks Coffee’s flavor graveyard. “Only it seems to be coming back stronger every year,” says flavor chemist John C. Leffing­well. As president of food and flavor consultancy Leffingwell & Associates, he dutifully takes reporters’ calls about pumpkin spice mania every time the leaves turn. He’s busy, given the recent proliferation of pumpkin spice products: bagels, hummus, even body butter and dog treats. Retail sales of pumpkin offerings have experienced double-digit growth for the past several years, reaching nearly $361 million in 2014, according to market research firm Nielsen.

And that figure doesn’t count Starbucks pumpkin spice lattes, which new product expert Lynn Dornblaser of market research firm Mintel Group credits with starting the trend: Starbucks has sold over 200 million since their 2003 debut.

Pumpkin spice backlash was inevitable. HBO comedian John Oliver has lambasted America’s obsession with “pumpkin-flavored science goo.” And food industry critic Vani Hari, who is better known by her blog moniker the Food Babe, triggered outrage when she wrote that pumpkin spice lattes contain “absolutely no real pumpkin.”

With apologies to the disappointed hordes, pumpkin was never the flavor intent. Pumpkins have volatile constituents, but they’re not the cloyingly sweet kind consumers expect in a dessert. A pumpkin spice product is made to evoke pumpkin pie, which, for the record, isn’t made with carving pumpkins either. The real filling is a specially bred sweet squash that is less fibrous and watery than a typical jack-o’-lantern gourd. The pie’s characteristic taste comes from cooked squash mingling with a spice mixture: cinnamon, nutmeg, ginger, and clove or allspice.

The pumpkin spice latte recipe is a closely guarded Starbucks secret. According to Leffingwell, it’s possible to create a pumpkin spice flavoring by steam-distilling pumpkin pie spices or performing extractions with solvents.

Unfortunately, it’s hard to ensure consistency in flavor strength or taste with natural spices, says Kantha Shelke, a food chemist with food science research firm Corvus Blue and a spokesperson for the Institute of Food Technologists. It’s more sustainable, she says, to use nature-identical flavor molecules in large-scale production. The combined mixture of cinnamon, nutmeg, ginger, and clove or allspice contains at least 340 flavor compounds. But human brains can fill in the blanks if provided with about 5–10% of that natural cornucopia. Major players include cinnamic aldehydes for cinnamon, eugenol for clove or allspice, terpenes such as sabinene for nutmeg, and zingiberene for ginger.

By themselves, however, spice compounds won’t create an appealing food flavor. Heating pumpkin spice ingredients together creates caramelized, slightly burned, wood-fired flavors and aroma compounds. These compounds—products of the Maillard reaction—are “what takes things from air freshener to food product,” Shelke explains. She’s not sure exactly what notes round out a pumpkin spice latte—“those are the treasured secrets of the flavor chemist,” she says. But cyclotene, the go-to compound for maple or brown sugar flavors, or vanillin are likely candidates.

That list of compounds makes sense to Donald E. Mencer. He and his undergraduate students at Wilkes University in Pennsylvania analyzed alcohol extracts of grocery-store-bought pumpkin pie spice powder with gas chromatography-mass spectrometry.

Although the data were what Mencer expected, some results surprised his students. Pinene, which turns up in cinnamon, nutmeg, ginger, and allspice, reminded the students of pine resin and wintry ever­greens, not tasty fall desserts.

UPDATE: This article was modified on September 29, 2016 to refresh its information and data.