My first million: Gary Hirshberg of Stonyfield Farm

Running a not-for-profit renewable energy centre in the early 1980s seems an unlikely foundation for a multimillion dollar business, but then Gary Hirshberg is not your run of the mill entrepreneur. Indeed, if you were to ask the now 52-year-old for his general thoughts on the world of business all those years ago, he would probably have told you that it "was all things evil" and that he "wanted nothing to do with it".

It's very different now. Hirshberg is the head of a $300m (£165bn) organic yogurt business now pushing into the UK. Preaching to disinterested crowds on the danger of climate change 30 years ago, he realised that he could change people's perceptions far more easily with a consumer product than he ever could through an NGO. "In hindsight, that assumption has proven to be true."

It was 1983 when friend Samuel Kaymen first asked him to come on board at his seven-cow organic farm in rural New Hampshire. Kaymen had "pioneered a fantastic yogurt recipe", which he was selling on to the local community. Word caught on, and soon enough they were selling throughout the state. By 1987, it was time to ramp up the business, and they made plans to move to a bigger dairy 50 miles away who agreed to take on production. Unfortunately, the dairy suddenly went bankrupt, leaving Hirshberg to watch helplessly as it was shut down. In one weekend, with orders rushing in from all sides, Stonyfield lost $400,000 in orders from a business that was turning over just $2m a year. They had to move back to the original small farm, but sales had grown well beyond its capacity. "We proceeded to lose $25,000 every single week... for about 50 weeks... All we were doing was trying to fill orders and not lose shelf space as I tried to figure out what to do."

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Keeping the business afloat wasn't easy. Sometimes, Hirschberg would call his in-laws in the middle of the night to borrow money for wages. "I'd... call [my wife's] mother, thinking Meg was still asleep, to see if I could borrow a couple of thousand dollars... and Meg would be on the other line telling her mother, don't do it'." But a canny eye for marketing helped. When a local DJ said he'd rather eat camel manure than Stonyfield yogurt, Hirschberg sent him the manure. "That ended up getting us air play for six months as this guy did have to actually admit that our yogurt did taste better than camel manure."

By 1992 Hirshberg finally had enough investors to fund expansion into a larger facility. This enabled them to sell to supermarkets in Boston, New York and all the way down the east coast. "We turned our first profit that year on sales of about $10m and then, as they say, never really looked back." Danone bought a majority stake in 2001 in a deal that allowed Hirshberg to stay as CEO.

So now he is heading for the UK, where organic food accounts for just a single-digit percentage of total food sales. "We believe we can add to the variety and help to grow organic there. It's only when we can penetrate to the double digits... that we'll be able to say that we've made a real difference."