Midway through their final semester at the Univeristy of California, Berkeley, Nikhil Arora and Alejandro Velez were getting ready for life in the corporate world. Despite the sluggish economy -- this was the spring of 2009 -- they had attractive jobs lined up, Nikhil as a consultant at PriceWaterhouseCoopers, Alex as a banker at Credit Suisse.

So what did they do? They chucked the job offers and began to grow mushrooms out of coffee grounds.

Two years later, they have no regrets. Their startup, called Back to the Roots, is literally a growth company: It sells mushroom kits that enable people to grow and harvest up to 1.5 pounds of gourmet oyster mushrooms in as little as 10 days, out of a cardboard box filled with used coffee grounds. Out of the box thinking, you could call it.

Despite a stumble or two, the company’s doing well. Back to the Roots sells the kits online and at Whole Foods Markets. It employs about a dozen people, most at a 10,000 square-foot warehouse in west Oakland, CA. Every day, they turn trash -- about 20,000 pounds a week of coffee grounds, collected from Peet’s Coffee & Tea outlets in Northern California -- into cash.

I spoke with Arora this week via Skype because I like businesses that find a way to extract value out of stuff that would otherwise be thrown away. That idea was what intrigued Arora and Velez, too; they were taking a class in business ethics when the professor, Alan Ross, mentioned that mushrooms could be grown from coffee grounds. After class, Nikhil and Velez -- who, until then, didn’t know one another -- approached him to learn more.