(Inside Science) – Saffron is the world's most expensive spice, costing up to $5,000 per pound. It is generally grown in arid regions where temperatures rarely drop below the freezing point.
Now, though, a team at the University of Vermont, in Burlington, is developing a process for growing the spice -- often used to color and flavor everything from rice dishes to main courses and desserts -- during the state's winter, when the temperature can fall far below zero Fahrenheit.
"We've grown it for two years under good conditions," said Margaret Skinner, a research professor in the university's Department of Plant & Soil Science. "It's fairly straightforward and easier than growing tomatoes."
If the team can scale up its research effort successfully, it promises Vermont's small farmers a subsidiary source of cash during the winter months, when they typically rely on low-revenue vegetables such as Swiss chard, spinach, and kale to maintain their incomes.
The project could also put a Made in America label on a product that currently accounts for more than 25 tons of imports to the United States annually. Iran currently grows more than 90 percent of the world's saffron crop. Spain and Italy are other major sources of the spice.
Growing saffron is not entirely foreign to the U.S. Amish farmers in Pennsylvania have planted it for 200 years, while the Iranian community in California grows small amounts. But the concept of saffron as a consistent revenue-producing winter crop is new.
Saffron's most common use is to complement food.
According to Susan Liechty, a lecturer on herbs who is a past president and current board member of the Herb Society of America, several research teams have studied saffron's potential role in treating stomach problems and depression.
For example, a review of scientific studies by scientists at Australia's Murdoch University in 2014 provided "initial support for the use of saffron for treatment of mild-to-moderate depression," while calling for further research "to expand our understanding of the role and actions of saffron in major depression."
The spice also appears in perfumes for men. Clothes manufacturers and rug makers traditionally used it to dye their products a deep red and similar colors.
Saffron originates in an unusual type of crocus that blooms in fall rather than spring. The plant starts life as a bulb called a corm that's similar to a tulip bulb. Each Crocus sativus plant contains violet petals surrounding three thin reddish orange threads, called stigmas, that are essential to the plant's reproduction.
"You plant the bulb and wait six weeks to two months," Liechty said. "When the blooms are almost open, you pick them and bring them where you can work with them, to pick the three stigmas and dry them."
Plucking the stigmas is a delicate, time-consuming process done by hand.
According to Arash Ghalehgolabbehbahani, an Iranian postdoctoral researcher who works with Skinner, a single gram of saffron requires the stigmas from 100 to 150 flowers.
"It's definitely labor-intensive," Skinner added. "The traditional argument is that saffron costs so much because it's so expensive to procure."
Ghalehgolabbehbahani, familiar with saffron growth in Iran's Khorasan province and aware that saffron corms can resist cold, inspired the project two years ago when visiting his wife, who was studying at UVM.
"Arash said one day: 'Why don't you grow saffron here?'" Skinner recalled.
She reported that the plants either froze to death or were eaten by rodents. But then she thought of high tunnels. These are plastic-wrapped structures like unheated greenhouses that have extended the green mountain state's growing season for winter greens by a month or more.
The tunnels are typically unoccupied -- and thus available to support saffron crocuses -- between December or January, when growers finish harvesting their winter greens, and March, when they plant tomatoes.
In summer 2015, Skinner and Ghalehgolabbehbahani planted some saffron corms in milk crates that they placed in high tunnels as winter approached. The crates protected the plants from rodents and made for easy removal of them from the tunnels when the spring brought warmer weather and growers needed the tunnels for their tomatoes.
The experiment proved remarkably successful.
"Our yield of the stigma was four times higher than in Iran," Skinner said. And analysis of the saffron by University of Mississippi biochemist Charles Cantrell revealed that its chemical properties equaled those of the spice grown elsewhere in the world.
The next step is persuading farmers to adopt saffron as a complement to their other products. Skinner and Ghalehgolabbehbahani have calculated that the spice could bring in $4 per square foot. That exceeds the $3.50 rate for tomatoes and $1.81 for winter greens.
Farmers could also sell the corms produced in the process, for 30 cents to $1 apiece.
"Each year the mother corm will die but produce several baby corms that survive," Skinner explained.
However, growing commercial saffron could face some difficulties at the beginning. As Ghalehgolabbehbahani pointed out, "You have to select good corms to start."
Liechty posed a practical question. "Will farmers be willing to pay the costs of harvesting it?"
To address those issues, Skinner and Ghalehgolabbehbahani hope to establish a North American center for saffron research and production. The center they envision would establish links among researchers and stakeholders and set up strategies to develop and expand market opportunities for saffron.
"The work we have done has sparked interest that could not have been there a few years ago," she said. "The center would be a catalyst to harness all of the interest."