The roads of rural India are thronged with food vendors selling fried snacks, spicy chickpeas, and fragrant breads. It's both a low-margin business and a dangerous one. The principal threat: cookstoves.

Svati Bhogle, the co-founder and managing director of Bangalore-based Sustaintech, was first drawn to the problem of cookstoves more than 20 years ago, when she was studying at the Indian Institute of Science. "In the developing world, wood is the primary source of fuel because it is cheap," says Bhogle, interviewed at the Social Venture Network conference. "You just go around and lop off branches." Over 4 million people a year--many of them women and children--die prematurely from illnesses attributable to household air pollution from solid cooking fuels, according to the World Health Organization. Beyond domestic kitchens, food vendors are also vulnerable to smoke and toxins produced by burning wood.

To address the problem, Bhogle and three other students designed a stove that eliminates smoke by improving combustion and heat transfer. The product had to be as cheap as possible, so the team made it from mud surrounded by bricks, with a gap between the two materials. "Mud is a natural insulator," says Bhogle. "It will absorb the heat up to a point. It keeps your food warm for two or three hours after it is cooked."

But testing the stove required access to the kitchens of rural households--access denied to Bhogle's male colleagues. "There are a lot of social barriers in villages, and kitchens are a place where you would not normally be allowed inside," she says. "But because I was a woman, I had that rapport, so they let me in." Bhogle observed cooking practices in roughly 30 homes, sprinkled throughout rice-eating, millet-eating, and wheat-eating regions. "I looked at their sitting posture, watched toddlers in the kitchen--everything related to comfort and safety that would make the stoves successful," says Bhogle.

Eventually, Bhogle and her colleagues expanded from household stoves to models for small industrial applications. To get their research to market, they established the Technology, Infomatics, Design Endeavor (TIDE), a not-for-profit group that works with small vendors to build and distribute stoves. "I would design a stove for use in herbal medicine and then transfer that design to a local entrepreneur," Bhogle explains. "Then I would help him set up a fabrication shop to make the stoves, and that would make him sustainable." By 2007, TIDE and its vendors had installed more than 10,000 stoves.

Then in 2008, TIDE received a high-profile Ashden Award for innovation in green energy. The £40,000 prize and accompanying publicity encouraged Bhogle to think seriously about scaling. "We were relevant to millions but just serving thousands," she says. A year later, TIDE's founders created Sustaintech as a for-profit initiative to manufacture and sell cookstoves to a mass market. (TIDE retains the intellectual property.)

Sustaintech targets small roadside eateries, whose owners earn less than $10 a day. The stoves cost $250 to $300. But because they are much more efficient, the food sellers--who typically buy firewood rather than collect it--save $1 to $2 a day on fuel costs. Still, "it was a very hard case to make," says Bhogle. "This is the first time they were investing in capital equipment for their kitchens. They did not have refrigerators or ovens. They agreed in principle that the product was good. But the price was high."

To make purchasing easier, Sustaintech allowed customers to try the stoves before buying and then to pay in installments. But customer financing was difficult: Microfinance organizations were dubious that food sellers would adopt the more expensive technology, and they preferred to lend to women in groups. Although the chairman of a major bank agreed to help, individual branch managers refused to service people with no bank accounts or credit histories. But customers borrowed from friends, neighbors, and family, and after a year or so, Sustaintech's installed base was sufficient to bring consumer-finance organizations onboard.

The customers themselves presented another challenge. "People would tell us, I would like a daily collection rather than pay at the end of the month. Because at the end of the month, I will have spent all the money I've saved," says Bhogle. The company compromised with weekly payments, handled by local agencies.

With all that IP already tucked under its belt, the company is understandably sales focused, with 20 of its 30 employees making the rounds of towns and villages. But thanks to word of mouth, radio advertising, and traveling demos, customers are also seeking out Sustaintech: 20 percent of sales are from people calling in. The company requires greater geographic expansion to increase profitability, says Bhogle. The stoves will work in any country where cooking practices are similar.

Since Sustaintech launched, a few competitors have emerged. But those companies' stoves are designed to burn fuel pellets, which they also sell. "They have a recurring revenue model," says Bhogle. "Their fuel is three or four times the cost of ours, which people simply harvest."

In addition to their benefits for health and air pollution, the stoves also reduce deforestation. Two acres of forest are preserved over each stove's five-year lifetime, Bhogle calculates, based on estimates that food vendors work eight to 10 hours a day, 330 days a year.

"I went into this to show that science and technology can be tools for social transformation," says Bhogle. "And that is what we are doing."