In the early days of Amy's Kitchen, founder Andy Berliner got a few calls a year from large companies looking to purchase the budding maker of natural frozen foods. More than 20 years later, the company now gets calls from suitors every single day.

Berliner says none of the offers have ever tempted him to sell the family business.

"We really kind of love what we're doing," he says. "In the long run, it's worth it to have that independence. Particularly if you like what you're doing."

Amy's has been a huge success story for an independent business that started with one frozen pot pie and has rocketed to control about half of the natural frozen food market in the United States. All through its growth, the company has held onto the core fan base that made it a hit in natural food stores in the late '80s.

In short, though the company has expanded to 1,800 employees and two plants with a third opening soon in England, no one has tarnished Amy's with the dreaded label of "selling out."

Berliner credits the success to ability to keep the business in family hands all these years, and a dedication to customer service that aims to provide everyone with the small-company feel. 

Keeping true to your roots can be tricky for independent businesses that want to grow and expand into new areas. No one wants to be seen as selling out the base as soon as a big paycheck comes along. Businesses who've forged ahead without ditching their roots offer these tips:

Expanding Without Losing Your Indie Culture: Focus on Customer Service

What's the main thing that separates an independent shop from a big box chain?

"All of it comes down to how they treat their customers," says Woody Sumner, publisher of the trade magazine Independent Retailer. "The price issue is always going to be an issue against the chains. The battle for the independents is won on the field of customer service."

Business observers say independent companies that have hit the big time always make their customers feel like they're still working with a small, personal operation. While a major chain might direct you to a call center or generic service e-mail, successful independents treat their customers with individuality.

"My wife reads every single consumer e-mail or letter," Berliner says. "And we respond to some of them personally.  That's basically what we are: we feel we are a service-oriented company trying to fill people's needs for healthy food."

Portland-based Stumptown Coffee Roasters has grown from one cafe in 1999 to three in Portland, two in Seattle and two in New York City today, plus a thriving wholesale business. 

The company has 150 employees, but 11 of those are full-time educators who teach others the proper way to make an espresso and serve Stumptown coffee. With such a big bicoastal operation now, the company wanted to make sure the quality isn't diluted, says Matt Lounsbury, director of operations.

"It can go right out the window depending on who's handling that coffee," he says. 

Stumptown also hosted a holiday party where it invited wholesale customers to play the video game Rock Band and interact with the company.

"A lot of our full time job is not just spending time with employees, its spending time with customers," he says. "[Sales people] spend better part of the week going out and seeing people."

How to Expand Without Losing Your Indie Culture: Stay in Touch

Successful independent companies not only respond to their customer concerns, they treat their customers as consultants and stay in touch constantly.

"Staying community based is important," says Kaya Oakes, author of the 2009 book Slanted and Enchanted: The Evolution of Indie Culture.

Need inspiration? Think about independent record labels such as Merge and Matador, which has thrived financially by working closely with artists and keeping up communication with fans. Doing so which builds credibility, Oakes says. Smart companies even seek their customers' input on business decisions.

"Crowdsourcing is a form of that," she says. "The companies are more willing to listen to their consumers, more willing to respond."

Keeping your customers in the loop on any changes makes them feel more connected to your company, Sumner says.

"You cultivate relationship with customers, notifying them of new products that they're going to be interested in on an ongoing basis," he says.

Having a set of values or ethics you share with the public helps, Oakes says, because it shows you stand for more than just making a profit. She says companies can gain easy cachet with their communities by contributing some money to charity or to help seed new local businesses.

Expanding Without Losing Your Indie Culture: Be Selective

It might seem counterintuitive, but if you have a strong independent base, you might want to ask yourself: Should I be trying to grow this fast at all?

Stumptown, for instance, turns down growth opportunities almost daily because they don't fit the company's standards, Lounsbury says. The company would rather grow slowly and selectively than seize every chance at expansion. It's not snobbishness; just smart growth, he says.

"We're still a small company," he says. "As we continue to focus on quality, we've continued to focus on who we've worked with. Our coffee's not for everybody."

Even with Stumptown's recent decision to supply a coffee stand in a terminal at New York City's John F. Kennedy airport, the company made sure the servers used the right equipment and passed a full training program.

"We're interested in people who will want to make good coffee," he says.

Berliner of Amy's learned the value of growing slowly the hard way. Before he was in the frozen food business, he ran Magic Mountain, an herbal tea company. He sold the company at an early stage but then watched it fall apart.

"It wasn't a very good experience," he says. "Stay financially strong. Grow a little slower than you could."

Expanding Without Losing Your Indie Culture: Know your Market

Finally, experts say you should respect your independent roots by knowing what your customers want.

Sumner says you can use your wholesalers as a resource on changing market trends if you're unsure what to do.

"Very often independent retailers rely on wholesale sellers of merchandise to inform them," he says. It doesn't hurt to talk to seek advice from other successful businesses in your market as well. "The people whose boots are on the ground and who are successful and are still open for business, generally, they're the one that independent retailers can learn a lot from."

When Amy's expanded into major supermarkets, health food stores fretted that the company was abandoning its small specialty store base. Eventually, the company was able to appease the stores by offering a more diverse line of products in health stores. 

"We said the company's goal is to make good healthy food available to as many healthy people as would want it," Berliner says. "Mass-market stores only carry a few Amy's products."

Stumptown made the decision to not expand into ancillary offerings such as T-shirts to avoid changing its image as a coffee-first company.

"We've only sold coffee," Lounsbury says. "We've continued to focus on that."