Joel Salatin is pulling on his braces. He's just had his picture taken wearing a suit – our photographer wants to show that he's not just a hands-on local farmer but also a new- era businessman – and now he's getting back into his work gear: muddy jeans, straw hat, and a farmhand's shirt that reads, in embroidered script, "Roy".

"Roy?" I ask.

Salatin follows my gaze to his chest and laughs. "The cleaner sells unclaimed ones for 50 cents each," he explains. "I might be Pedro one day, and Roy the next."

Such is the unpredictable world of Joel Salatin, hero of the new local food movement, feted for his ingenious chemical-free farming methods and admired for his outspoken articulacy on the horrors of industrial food.

We are at Polyface, the small farm his family has run since he was four years old (Salatin and his wife Teresa now have two grown-up children of their own, who also work there). The rambling white clapboard farmhouse – a gold plaque above the fireplace designates it a historic landmark, built in the 1750s – stands in an absurdly picturesque landscape in Virginia's Shenandoah Valley. On the January day we visit, 24 inches of snow have fallen in a few recent hours and turned the surrounding fields into rolling white patchworked dunes dotted with black cows. And as if its children's-book looks were not enough, the roads have names like Cattleman and Sugar Loaf and Buttermilk Spring.

The farm is closed to visitors during these months, the coldest of the year; the purpose of this period, as Salatin writes on the Polyface website, is "the rejuvenation of the Salatin family". Needless to say, they are not just sitting around. Farmhands are cleaning out the hens' hoop houses out back; a new batch of live-in apprentices is building a temporary structure next to the tractor garage; Teresa is dealing with admin and taking down the Christmas tree. And Joel has dashed off another book over Christmas. His many self-published tomes, which offer first-hand guidance on how to repeat his successful experiment, have wonderful titles such as Everything I Want To Do Is Illegal and (the new one) The Sheer Ecstasy of Being a Lunatic Farmer.

Salatin, who has been farming in this way for years, came to more widespread attention thanks to Michael Pollan's bestselling book The Omnivore's Dilemma – he refused to ship meat to Pollan outside of the meat's own bioregion, and became an important figure in the book. Now he provides the charismatic moral backbone of Food, Inc, a hard-hitting documentary featuring Pollan and co-produced by Eric Schlosser, the investigative reporter who wrote Fast Food Nation.

Food, Inc suggests some shocking links between big government and big business in the food industry, along with some appalling statistics. For instance, in the 1970s, the top five beef packers controlled 25% of the market; now the top four control more than 80% – meaning that if ever meat is tainted by bacteria or chemicals it has the potential to reach vast numbers of people; in 1972, 50,000 food safety inspections were conducted by the US Food and Drug Administration, and three decades later that number had gone down to 9,164; 70% of all processed foods have some genetically modified ingredient; in 2007, E coli from food affected 73,000 Americans – something the film correlates directly with the increase in consumption of processed foods and the scale and cleanliness of the country's huge industrial slaughterhouses. But beyond the statistics, the sheer sight of carcasses being dunked in ammonia, endlessly and mechanically, would make any meat eater want to stop eating meat. The very banality of it – the fact that we could, the filmmakers suggest, change the world with every bite yet somehow refuse to – is horrifying.

The first thing I ask Salatin when we sit down in his living room is whether he's ever considered becoming a vegetarian. It's not what I had planned to say, but we've been in the hoop houses with the nicely treated hens, all happily pecking and glossy-feathered, and I've held one in my arms. Suddenly it makes little sense that this animal, whose welfare has been of such great concern, will be killed in a matter of days. Naive, I know, and Salatin seems surprised. "Never crossed my mind," he says. The problem that's leading the "animals-are-people movement", as he refers to it, is two-fold, in his view. First: "The industrial food system is so cruel and so horrific in its treatment of animals. It never asks the question: 'Should a pig be allowed to express its pig-ness?' And the second thing of course is the urbanisation of the world, to the point where people are not now connected to their ecological umbilical, so that the only connection anyone has to an animal is a pet cat or a pet dog. And that really gives you a very jaundiced view of cycles of life – death, regeneration."

It's true that America is particularly susceptible to this – even without knowing much of the information revealed by Pollan or Schlosser or Food, Inc director Robert Kenner, you sense it. The US is especially blind to it for the sake of convenience or affordability. But living in a city like New York, as I do, on the occasions when you allow your field of vision some leeway – into the future health of your children, into the vastness of the country – you see how integral the city's relationship to the origins of its food is to its profound ill health. The enormous quantities produced by the few monopolies in power, the distance food travels to get to your door, the bounteous look yet empty, aqueous taste of its fruit.

I ask Salatin when he first realised his country was poisoning itself.

"Well, goodness," he says, and reaches back into the learned resources of his mind. "Chemical agriculture really started with Justus von Liebig in 1837 [Liebig was the father of the fertiliser industry, and also the father of the Oxo cube], telling the world that: 'Oh, a plant is really only nitrogen, potassium and phosphorus.' I think it's important to understand that in the big historical context of things, there has been land degradation from civilisation since the beginning of history. I mean, the Rajputana desert in India is a manmade desert caused by overgrazing. Land degradation did not start with chemical agriculture. But chemical agriculture offered new tools for annihilation."

But what, I press him, can we say about the moment we're in now? Are we in a state of crisis or a continuation?

Salatin quotes Joel Arthur Barker on paradigms – every paradigm, he says, exceeds its point of efficiency. Agriculture is always the last sector to join the new economy, because farmers are very conservative. So only now has the industrial paradigm in agriculture come to the end of its workability, Salatin explains. "What happens is all these things we're seeing – campylobacter, E coli, mad cow, listeria, salmonella, that weren't even in the lexicon 30 years ago – that is the industrial paradigm exceeding its efficiency. So these Latin squiggly words that we're learning to say – bovine spongiform encephalopathy – are nature's language screaming to us: ENOUGH! And the question then is: what will it take for us to listen? And my contention is that Wall Street is still wearing conquistador mentality and uniforms, and nobody is listening to the pleadings of nature saying: 'Enough.'"

Salatin says he thinks that in the clash between artisanal and industrial "we're just beginning to see the tip of the iceberg", and he doesn't like to predict who will win. Personally, he tries to be an optimist, but he adds ominously that "time will tell. Who would have thought in 1925 that six million Jews would have been gassed in Germany? A lot of crazy things have happened in history".

Human arrogance is one thing Salatin strongly warns against. Of course, it's one way of explaining the large-scale upset to the natural order of things. But Salatin also thinks the way you treat animals is a reflection of the way you will go on to treat human beings. One of his more romantic and far-fetched-seeming statements in the documentary is to this effect, and it turns out to be one of the most centrally, shockingly true: the treatment of illegal workers by big food corporations. Films like Food, Inc, Salatin suggests, are finally "exposing the kind of corruption and evil that is the shortcut. What happens when you don't ask: how do we make pigs happy? Well, you view the pig as just a pile of protoplasmic structure to be manipulated however cleverly human hubris can imagine to manipulate it. And when you view life from that kind of mechanistic, arrogant, disrespectful standpoint, you very soon beginto view all of life from a very disrespectful, arrogant, manipulative standpoint. And the fact is, we aren't machines."

It's probably safe to say that not all farmers in Virginia speak like this. Salatin, the son of an economist who moved here and turned local chemical farming habits on their head, was born in Venezuela and worked as a reporter for the local newspaper in Staunton, Virginia before he came to work at the family farm. He met Teresa when they were in high school and married her almost 30 years ago.

Salatin is a remarkably youthful 53-year-old: his skin is strangely unweatherbeaten, and his eyes, behind large square glasses, are full of life. He writes prolifically and commands several thousand dollars a pop for public speaking engagements on topics such as "Dancing with Dinner", "Holy Cows and Hog Heaven" and "Forgiveness Farming". He's funny, informed – he thinks nothing of dropping Louis Pasteur or Sir Albert Howard into the conversation – and rewardingly heated in his arguments. He also seems to have come into his own somewhat. When I ask him what he and his wife disagree about, given that they have worked together so closely for so long, he says he has to respect her need for privacy, while she has to put up with his exercising his own very particular gifts: "I'm out here in my world of people and parties," he says, "and she's being crushed. But she appreciates that this is where we are now. I need people – theatrics and schmoozing and storytelling are part of my talent."

Now, perhaps we can all easily agree that eating Salatin's meat is better for us (and I can certainly vouch for its tastiness, having had Polyface chicken in a local restaurant in Staunton), but getting down to basics, I ask him if I were from Mars how he would explain why I should eat his meat. Salatin offers five reasons.

"The first thing is," he says, "it's safer from a bio-security standpoint. If you eat our stuff, it's gonna be only sold real close right here. There's a short chain between field and fork, and the shorter that chain is – the fresher, the more transparent that system is – the less chance there is of anything from bio-terrorism to pathogenicity to spoilage. You wanna get diarrhoea? Eat industrial food.

"Number two is what I would call your own personal immune system." The more antibiotics are given to the animals we eat, he explains, the less responsive we become to antibiotics when we need them for medical reasons. "You've been drugging yourself at dinner every day."

Thirdly, he goes on, they've had their meats checked, and they are unequalled in their nutritional density and power, however you want to measure it – "Omega 3, omega 6 ratios, riboflavin, polyunsaturated fats, vitamin A…"

Four: it tastes better.

"And the fifth reason," he concludes, "is: it's better for the environment. It's a very landscape-therapeutic production model."

So: we know why we should eat this. How many of us can? Salatin currently feeds between 7,000 and 9,000 locals. That's a tiny proportion of the American population; how sustainable is his system?

"Can I feed the world? That's a wonderful question, one of my favourites," Salatin smiles, having more or less asked the question himself. "Not only can we feed the world, this is the only system that really can feed the world."

And, I ask, what happens to the next 9,000 people, and the next and the next?

"Well, there are a couple of answers to that," Salatin replies, taking off into vivid detail about a small part of how he actually operates. "Let's take cows, for example. With good, controlled grazing, where we're moving these cows every day to a new patch, on our farm we're averaging 400 cow days per acre – a cow day is what one cow will eat in a day. Our county average is 80. Because grass grows in an S-curve, so when you have cows in continuous grazing, they keep the grass short, in what I call its nappy phase. And what we want to do is get it in its juvenile adolescent growth curve. We don't want it to grow into what we call nursing-home grass. I say this not for humour – it is funny, but: everybody can understand that. People grow faster between 12 and 18 than at other ages. And so if we can maintain the forage in that fast juvenile-growth stage, then we are metabolising way more solar energy in the biomass than you are at any other time in the growth cycle of the plant. And to do that, you have to manage the meeting between cow and grass. You can't just turn the cows out and hope that it'll happen, because it won't. Cows always eat dessert first."

So, I ask, you're saying this particular system of management and growth could be taken anywhere in the world and replicated?

"Absolutely."

And why are people not doing that?

"Well, I don't know," Salatin says, stretching his shoulders into an exaggerated shrug. "Why don't people like the truth? It's a big question. One answer is: it hasn't been done before. It's just not what Grandpa did. And remember, farmers are conservative. If the neighbour doesn't think it's a good idea, it's not a good idea. Whereas my position is: a good idea is what the neighbours think is a terrible idea!"

Just on principle, I laugh. Salatin is marvellously perverse. "Exactly," he says. "You know it won't work if the neighbours think it will."

You must have terrible neighbours, I suggest.

For a second, he pauses. "No, we have wonderful neighbours! And the other thing is, if everybody started doing the kind of farming we do, it would completely invert and realign all of the food-system power economic structure in the world. We're looking at cultural revolution – that's what this is."

Salatin is not entirely without critics – I don't mean big-brother big-business bad-guy critics; I mean people who are trying to do the same thing in a more purist way and regret that he is being hailed as the saviour. In Jonathan Safran Foer's new book Eating Animals, a poultry farmer named Frank Reese, who raises heritage breeds only, not birds whose genes are identical to the industrial birds, criticises Salatin in these terms. "That farm is a joke," Reese says of Polyface. "Joel Salatin is doing industrial birds. Call him up and ask him. So he puts them on pasture. It makes no difference. It's like putting a broken-down Honda on the autobahn and saying it's a Porsche."

I put this to Salatin, and initially he denies it. "That's just wrong," he says defensively, "Just because it's in print doesn't mean it's true." Salatin doesn't know Frank Reese. He asks if Reese is in favour of using only heritage breeds, and I say that's my understanding of it, yes.

"OK," he concedes. "You know what, that's fine if you want to do that. I'm not opposed to heritage breeds. We have some heritage breeds. Here's the problem though: marketability. When you say: 'Can we feed the world?', we're not going to turn around the system by feeding only 10% of the population. We gotta feed 90%."

You don't think people will pay…

"Double?" he says, finishing my question. "No, they won't. And besides, it's all dark meat. No double breast. Hey, 40 years ago, every woman in the country – I'll be real sexist here – every woman in the country knew how to cut up a chicken. When we started doing these pastured chickens, it was a moot point. Nobody asked for breast – it didn't exist! I mean as a separate item. Now 60% of our customers don't even know that a chicken has bones! I'm serious. We have moved to an incredibly ignorant culinary connection."

Salatin is hitting his stride now. "We tried heritage chickens for three years and we couldn't sell 'em. I mean, we could sell a couple. But at the end of the day, altruism doesn't pay our taxes. And I'm willing to say: 'You know what? I don't have all the answers and I pick my battles and compromises.' If you want to get brutally honest, in my opinion we shouldn't even have egg sales in America! Every restaurant and every home should have two or three chickens. I mean, you got a parakeet, why not have two chickens? You get eggs instead of a parrot keeping you awake at night. In a perfect world, that's how it would be."

This tirade from Salatin is quite a performance, and not without good, convincing intentions. But it's also peppered with apparent contempt, which makes one wonder: is he the spiritual, crusading zealot he appears to be? Who is he trying to save: us, the world, or farmers like himself? His answer to this question is that you can save all of those at once, if only people would "take charge of their food system". Let's hope he's right.

Salatin looks at his watch. While we pack up, he attends to other things. We wait around to say goodbye, but he's on the phone, and it looks like it's going to be a long one. He's launched into his spiel again with gusto, and he gives us a smile and a wave, talking into the receiver all the time. We ask Teresa who's on the other end of the line.

It's Oprah – naturally.

Food, Inc opens on 12 February. We have two pairs of tickets to the premiere to give away, see www.observer.co.uk/foodinc for details

Dishing the dirt – the author of Fast Food Nation and co-producer of Food, Inc, and the director of the film discuss the american food industry

Eric Schlosser "We showed the film to the head of the US Department of Agriculture and he seemed very sympathetic to it, but his argument was: 'Make us do it.' There is so much resistance to change that you really need a movement. Of all the sorts of reforms, the one that will be easiest to do in the US is food safety, because there's not a big popular lobby for 'shit in the meat' – Republicans, Democrats, if you ask them: 'Do you want faecal material in your hamburger?', most people say no. The regulatory changes to food safety are very simple – Kevin's Law [named after a child who died after eating E coli-contaminated meat] would mandate that meat is tested as it leaves the plant. This isn't about a socialist revolution. This is about: if there's deadly pathogens in the meat, you're not allowed to sell it. If we find it, we're allowed to take it off the shelf. I'm optimistic about the possibility of that change. The industry line is: just cook it. It's a way of shifting responsibility away from selling a tainted, faulty product, and onto the consumer. The ultimate message is: if your food's poisoned, it's your fault. If you're obese, it's your fault."

Robert Kenner "It was amazing making this film. I had no idea food was such a litigious subject. Kevin's mother is asked how his death changed her eating habits, but she can't answer on film because she fears she could be sued by the food industry. I was dumbfounded. She mentioned Oprah [who was sued by Texas beef producers for saying on her show that she would never eat another burger after a segment on BSE in 1996] and I knew about that, but when you connect the dots it becomes a lot more insidious – and in context it made me really scared! We were certainly attacked on a regular basis – several websites were set up to attack the film. We had every word verified three times. We had to negotiate everything. I spent more on legal fees on Food, Inc than I did on my past 15 films, times three.

"One of the big arguments in the US is that it's your responsibility to eat better, but there is a massive amount of effort going into working out how to sell us more calories, to feed our addiction – billions of dollars to figure out how to get you to want their food and to continue the myth that our food comes from a farm with a picket fence and a red barn, when in reality there are a few companies that own products under a lot of different names. We've been so removed that we think chicken is grown in little strips. We subsidise food in the United States that makes you sick. The fact is, we love cheap food, and I'm no different.

"But the job of the film is to say that this food is much more expensive than it looks. We need to start taxing things that make us sick, in the same way we dealt with nicotine. Food, Inc has become an Inconvenient Truth-type of film – the debate is very new in the US. There is a growing food movement, but Food, Inc helped explode it – Michael Pollan had bestselling books before, but now he's being outlawed on college campuses. The food corporations are funding these universities and they say: 'You'll lose your funding if he goes on stage without someone else to counteract what he's saying.' But their market surveys are saying: 'You'd better start listening.' So I'm getting invited to conferences to speak to people from food corporations who'd probably like to shoot me. " Rebecca Seal

The US food industry response to the film can be found here: www.safefoodinc.com

In response to Food, Inc, the US food industry launched www.safefoodinc.com, which says ,"US meat and poultry is among the safest, most abundant and most affordable in the world… We have achieved success through research, technology and plain hard work."