Once a month a tractor-trailer rolls up to the Family Early Learning Center, a one-room preschool in East San Jose, Calif., that doubles as a food pantry for poor families with young kids. On a bright Friday in August, a dozen or so women from the neighborhood gathered for the truck's arrival. Volunteers as well as customers, they had come to help unload the monthly delivery of groceries from the local food bank.

The truck driver moved a huge pallet of potatoes onto a pallet truck and rolled it to the door of the school. Then came big, round watermelons; then purple onions.

"Cantaloupe?" the driver called out, wondering where to unload it.

"We're going to do that outside," a woman answered.

The women broke down the pallets as fast as they could. A crowd of customers would gather soon. Anything the women could carry went inside the school - boxes of celery, onions, eggs, pinto beans, generic corn flakes, rice and creamy peanut butter. Outside, the driver unloaded green peppers, plums, apricots, bags of potatoes, ears of corn and pears, arranging everything in two rows of big, open bins.

It didn't look like food for the needy. It looked like a farmers' market.

Traditionally food banks have gathered mostly leftover or damaged boxes and cans from supermarkets, food processors and other mass distributors and then passed along the food to soup kitchens and food pantries like the one in East San Jose. Food banks have always found some fresh produce to give away; a few have managed to give away a lot. But for the most part, they have trafficked in processed foods -- widely available free, simple to transport and warehouse and quick to fill empty stomachs.

Increasingly, though, food banks have been looking to agriculture. California is at the forefront of this change. Since 2005, the California Association of Food Banks has struck deals with farms and packers across the state, where, on behalf of its members, it collects truckloads of fruits and vegetables that are too small, ripe or misshapen for supermarkets to sell.

This shift toward more healthful food is partly about obesity and its rise among the poor. But it's also a product of necessity: the food industry has become more efficient, squeezing the traditional supply of surplus cans and boxes. Fresh food offers a big, new food supply -- and maybe, for the food banks themselves, a beneficial new role.

"There's an almost unlimited supply of produce that's not being adequately distributed," says Vicki Escarra, the president of Feeding America (formerly America's Second Harvest), the national network of food banks. Last month she formed a fruits-and-vegetables task force and plans to bring in 25 percent more farm produce through national donors in the next fiscal year. "Identifying where it is and how we can get it and how we can subsidize it -- there are a lot of lessons that can be learned in California," Escarra says. "What they're doing is really innovative."

Bill Foltz stood ankle deep in sandy soil. It was a scorching September afternoon in California's Central Valley. Beside him, a farmer named Nathan Mininger dusted off a sweet potato and took a bite. Foltz works for the California Association of Food Banks, for the Farm to Family project. He and his colleagues are a bit like "gleaners" - the church or charity volunteers who walk the fields after a harvest and carry home leftover fruits and vegetables in gunny sacks. Foltz, however, deals in 20-ton loads and commercial freight. And for the right crop, he can offer a few pennies a pound.

Late last harvest season Foltz met Mininger for the first time at a nearby food bank, where Mininger donated some sweet potatoes now and then. A few weeks later they met for coffee at an old diner off a narrow country road. Foltz was looking for a big haul of free sweet potatoes. "I'd quickly realized that wasn't going to happen," he recalled to me, "not in the volume I was looking for."

The reason was simple. Supermarkets buy the best sweet potatoes -- good size, smooth skin, not too crooked. But just about all the rest, the "No. 2's," farmers can sell to food processors, for everything from fries to baby food. With most crops Foltz can watch the market and solicit donations when he sees that a glut from a big harvest will perish in storage. But not with sweet potatoes. Kept cool and dry, they can last a whole year. Sellers can be patient.

Foltz was motivated, though. Sweet potatoes are one of the most healthful and hearty vegetables in the produce aisle: they're so prized, and so hard to get, that food banks in California paid more per pound for sweet potatoes than for any other fruit or vegetable last season. Foltz explained all this to Mininger, as the two men drank their coffee.

"It's too bad you can't use white sweet potatoes," Mininger said. He explained that high-end supermarkets will pay a premium for No. 1's, but there is no demand for white-sweet-potato fries or white-sweet-potato pie filling. So, unlike with regular sweet potatoes, a white-sweet-potato grower picks only the best potatoes and leaves a lot in the field.

Foltz was intrigued. He and Mininger headed out to the field together to have a look. They followed a harvest crew as it inched down a row. A big blue tractor pulled a shaded, mechanized harvester, carrying six workers in hats and bandannas, and six large wooden bins. A conveyor belt dug white sweet potatoes out of the sand. The workers chose the best ones, put them in bins and let the rest drop off the back of the belt to the ground.

Foltz chatted with Mininger about the added cost of collecting those No. 2's. Mininger said he could do it for a relatively minimal fee and break even, because his workers were already there collecting the No. 1's.

When Foltz returned to the fields in September, for the first day of this year's harvest, one of the six wooden bins had been replaced by a cardboard bin, for the food banks. Foltz and Mininger stepped aboard and peered into the bin, which was slowly filling with small sweet potatoes. In a few days the first shipment would be on a truck bound for Oakland, San Jose and San Francisco. They might get half a million pounds or more by season's end. "This," Mininger said, "is what Mr. Bill is going to feed the world with."

A few days later I drove out to the Alameda County Community Food Bank, a big warehouse near the Oakland airport. A group of volunteers from Chevron, in matching company T-shirts, sorted and bagged ears of corn and red plums that arrived the day before. Five years ago, less then 10 percent of the food that passed through Oakland's food bank was fresh produce -- a pretty typical figure, nationally. Today, fruits and vegetables account for almost half. The Second Harvest Food Bank of Santa Clara and San Mateo Counties, which serves San Jose, has nearly tripled the amount of produce it distributes. At the San Francisco Food Bank, 60 percent of the food that it gave away last year was fresh fruit or vegetables.

Sorting corn and plums is a far cry from the way things used to work. When food banks spread across the country in the 1970s and '80s, a food solicitor at a bank would contact supermarkets, food processors and distributors and arrange to pick up truckloads of dented soup cans or breakfast cereal that got lost in a warehouse and passed its sell-by date. Then volunteers from local soup kitchens, food pantries and church groups would show up at the food bank in vans and station wagons and take the food back to their neighborhoods.

But the food industry has cut back on waste. Factories are quicker to catch mistakes on a production line. Computerized inventory means stores have a better idea what to order, and when, and fewer shipments get lost or expire. Manufacturers have changed the way they reimburse supermarkets for damaged goods, too. The Grocery Manufacturers Association says that unsalables, as a share of gross sales, have fallen significantly since 2005.

There is still surplus and damage and waste. But food businesses have other ways, now, to unload it. Dollar stores and discount outlets have boomed in this decade, and increasingly they buy and sell food -- including leftovers and unsalables that food banks used to get free. Donations of unsalables to Feeding America have fallen at least 7 percent a year for eight consecutive years. The San Francisco Food Bank saw donations from manufacturers drop 18 percent in the last year alone.

A few years ago, San Francisco's food bank anticipated this crunch and began to look farther afield for sources of food. Food banks were traditionally expected to solicit food in only the counties they served. But San Francisco seemed just about tapped. California's big rural middle, meanwhile, had lots of farms and food manufacturers and presumably more surplus food. A volunteer named Gary Maxworthy, a retired executive from a big food distributor, proposed that Northern California's food banks hire a shared roaming solicitor, to look for missed opportunities across county lines.

The food banks assumed that they would turn up more boxes, more cans. But they found peaches -- from a big stonefruit packer in Fresno, Calif., which was regularly donating as many peaches and nectarines as Fresno's food bank could accept and was still dumping millions of pounds of fruit each year, some of it perfectly edible. That gave the food banks an idea. In 2005 they decided to turn their roaming food solicitor into a farm-produce solicitor, and Farm to Family was created. Foltz, a retired logistics manager from a big poultry company, set out looking for fruits and vegetables. He wouldn't be bound by local demand or capacity; Farm to Family could ship wherever there was need. The group would even design delivery routes so that big food banks could get full 20-ton truckloads and smaller food banks could share an order.

That first year Foltz found 10 million pounds of fresh produce, mostly peaches, oranges, watermelons and potatoes. "We were pretty proud of ourselves," he said to me, laughing. "We had no idea how much was out there."

Foltz is one of three Farm to Family solicitors now, including a retired fertilizer and pesticide salesman and a part-time hay farmer. Together they're on pace to bring California's food banks more than 80 million pounds of produce by the end of this year, including 66 different kinds of fruits and vegetables, from spinach and cauliflower to pluots, rainbow chard and honeydew. And they expect to find much more.

Each crop presents a different puzzle. Take carrots. According to Foltz, just two California firms supply a huge share of the national market. "And they're vertically integrated," he explained. "They'll grind the big ones down into baby-cut carrots and charge for that. They do carrot juice. They do shredded carrots for prepackaged salads." That makes them unlikely to sell anything at or near cost, much less to donate large quantities. So Foltz has to concentrate on smaller growers and packers.

Peaches, plums and nectarines are much easier to source. Farmers pick just about everything off the trees and take the harvest into a packing shed, where it gets sorted into grades and boxed up for delivery to supermarkets. But the fruit is fragile and it turns quickly, and there isn't much of a juice market, which means that packers have few options for unloading their ripening surplus. That makes it an easy target for Foltz.

But the very reason that soft, quick-ripening produce is so often available also makes it a challenge for food banks to handle. When Oakland's food bank moved into a new warehouse in 2005, it installed a huge cooler, as big as a suburban house. Suzan Bateson, the food bank's executive director, recently took me on a tour. "We built this with the vision that it would be our future," she said, as we stood shivering inside. That year her food bank became one of the first in the country to ban donations of carbonated beverages, which meant an immediate hit of roughly a million pounds to the food bank's most important statistic: pounds distributed. "I made a promise to the board that I'd replace it with fresh produce," she said.

Around that same time, food banks across the country were beginning to look more closely at the food on their shelves. "When I first came to the food bank, a lot of the shipments were snack food and candy," says Paul Ash, director of the food bank in San Francisco. Food banks have always preferred more healthful food, of course, but that didn't seem nearly as urgent as empty stomachs. Suddenly, facing all the illnesses associated with obesity, from diabetes and heart disease to hypertension, it did. "It was like getting hit in the head with a hammer," Ash says, "realizing that hunger and obesity could occur together."

And so fresh produce has seemed increasingly worth the cost and the difficulty. Nationally, Feeding America has negotiated deals with giant supermarket chains, including Kroger and Wal-Mart, to salvage unsold produce, as well as meat, dairy and prepared foods before they spoil. It recovered 198 million pounds last year, up from 96 million the year before. The Vermont Foodbank actually bought its own 20-acre farm last year, and food banks across the country have contracted with growers or planted crops on their own small plots of land. (Such efforts have required food banks to raise more money. It's not always an easy sell to donors; people like organizing food drives. But it usually makes sense: the money spent on a $2 jar of applesauce could otherwise buy up to 40 pounds of Farm to Family apples.)

California's bigger food banks have increasingly delivered their goods rather than having pantries come pick up the food. Produce often arrives near the end of its shelf life, and shoestring pantries can take only so much away. Early on, Oakland's food bank set up a shipping route and sent a refrigerated truck around the county. Then it added another truck and more routes. Now it enlists five refrigerated trucks, each one stopping at as many as 15 or 20 local food pantries, schools and church parking lots each day and depositing only as much as an agency can give away in a couple hours.

When the vegetable in a big haul is a little out of the ordinary -- say, artichoke or eggplant -- the food banks even send along recipes to encourage customers to make use of it. "These efforts have dispelled the myth that low-income people don't eat fresh produce because they're too dumb or whatever," says Joel Berg, director of the New York City Coalition Against Hunger. "Pantries will say their customers love, love this stuff."

On the day of my visit, Michelle, a woman at the Family Early Learning Center, took two bunches of celery from inside the preschool and then stepped outside. She was full-figured, with a kind, round face, her hair in a messy bun. She added pears and peppers and bananas and plums -- a couple or three of each -- until her small cart was full.

Feeding America estimates that demand at food banks, nationally, has increased 30 percent in the last year, in some communities as much as 150 percent. In a survey last month, 98 percent of member food banks said that the increase was due mostly to people seeking emergency food for the first time. Michelle worked full time as a janitor for the last nine years, all for the same company, and made $320 a week. In July she lost half her hours, and her mother moved in, to recover from heart surgery. So she found this place.

She can afford peanut butter, she said. But free fruits and vegetables are a big deal. She just started volunteering at a community garden that rewards its volunteers with small bags of vegetables. "Since my hours went down, I look at the Safeway ads and get whatever is cheapest," she said. "You don't get very good food." I asked what she and her son typically ate. "Eggs with hot dogs cut up," she said, pausing to think. "Rice and beans. Yeah." She will eat better this week; and maybe next week. But nutrition will remain a luxury - especially on her salary; prices for fresh produce, she notes, remain high. Still, she said, placing her groceries in the car with care, "I'd rather do fresh than frozen."