EAST LANSING, Mich. (AP) — There’s a surprising amount of science in a bag of potato chips.

Researchers have spent decades developing potatoes for chip makers that can grow in all kinds of climates, avoid diseases and pests, sit in storage for months and still deliver a satisfying crunch. They’ve also kept an eye on consumer trends; a shift to snack-size portions has increased the demand for smaller chipping potatoes, for example.

“The potato industry is dynamic,” said David Douches, a Michigan State University professor who leads the school’s Potato Breeding and Genetics Program. “The needs change, the costs, the pressures that they have, and the markets change. So we have to adapt to that with our varieties.”

Douches has developed five new potato varieties for chips in the the last 15 years. His latest breakthrough is a bioengineered potato that can maintain a proper sugar balance when stored at colder temperatures, which can help keep potatoes from rotting. He is currently growing seeds for commercial testing of the potato, which is not yet on the market.

Douches’ work helps fight world hunger; he has developed disease-resistant varieties for farmers in Nigeria, Kenya, Rwanda and Bangladesh. But he’s also helping U.S. chip makers, grateful snackers and Michigan’s $2.5 billion potato industry. While Idaho leads the U.S. in potato production, Michigan is the top producer of potatoes for chips.

There are around 50 unique potato varieties grown for chips in the U.S. right now, according to the National Chip Program, a cooperative that brings together Michigan State and 11 other university breeding programs with growers, companies that make chips, and the U.S. Department of Agriculture.

Efforts to improve those varieties are constant. The National Chip Program evaluates around 225 new potato varieties each year and selects 100 for further trials, said Tim Rendall, the director of production research at Potatoes USA, a trade group that oversees the chip program.

The close partnership between researchers, farmers and potato chip companies is unusual in the food industry, said Phil Gusmano, the vice president of purchasing at Better Made Snack Foods, which has produced potato chips in Detroit since 1930. Better Made worked closely with Douches when he was developing two of the varieties the company uses now, Gusmano said.

“We were able talk about size profile and different needs that make a really good chip,” Gusmano said. “And the great thing is, they’re willing to listen to what we have to say, because if they put together a potato that doesn’t really meet the needs for the end processor, it doesn’t do them any good.”

Breeding a new type of potato can take up to 15 years, Douches said. The simple potato has a surprisingly complicated genetic structure, with four chromosomes in each cell compared to two in most species, including humans. That makes it harder to predict which traits that cross-bred plants will inherit, he said.

“We’re never able to fix a trait and carry that over to the next generation, so it’s very difficult to find a potato that has all the traits that we want,” Douches said.

Douches became fascinated with potato breeding and genetics while in graduate school. At Michigan State, he focuses on chipping potatoes, since Michigan is a leading producer. Around 70% of the state’s potato crop is destined for chip processing, according to the Michigan Ag Council. The trade group estimates that one of every four bags of potato chips produced in the U.S. contains Michigan potatoes.

Breeding potatoes that can sit in storage for nearly a year has been one of the biggest challenges in Douches’ 40-year career. Historically, farmers harvested potatoes and then stored them in huge piles at around 50 degrees Fahrenheit (10 degrees Celsius). Temperatures any colder cause sugar levels to rise in the root vegetables, and higher sugar content leads to darker potato chips. But warmer storage conditions can lead to rot.

“You think they’re just these inanimate objects, but they actually are respiring and breathing,” Douches said. “When you do that to them, you’ve got, like, a two- to three-day window where they’re happy.”

His Manistee variety, which was released in 2013, can be safely stored until July at 45 F (7.2 C) degrees. His new bioengineered potato can be stored at 40 F (4.4 C).

Gusmano said Better Made used to source potatoes from outside of Michigan for half the year because the Michigan potatoes it harvested in the fall only could be stored until February. The company now uses newer varieties, like Douches’ Mackinaw potato, which can be stored until July and is resistant to several common diseases.

“We’re not shipping potatoes from all over the country to be fried here in Michigan,” Gusmano said. “Instead, they’re being shipped from an hour and a half away all year long.”

Dee-ann Durbin And Mike Householder, The Associated Press