Gordon Muir had an epiphany while looking through old photos of The Varsity, an Atlanta-based quick-serve chain established in 1928 by his grandfather Frank Gordy. In the photos, he saw in-store banners and buttons advertising the brand’s noncarbonated beverage, Varsity Orange.

“And I thought, ‘Man, we’re not doing that,’” says Muir, president of The Varsity. “We were really missing the boat. Our gross profit is so much higher on that product because we make it in house every day and have for 80 years.”

At the time Muir came to the realization, the chain was selling about 5,000 units of Varsity Orange (VO) per year. Many of the chain’s younger customers didn’t even know about the drink, which Gordy invented in 1932 after tasting something similar on a New York City street corner.

In June, Muir decided to celebrate VO’s 80th anniversary by giving away the orange beverage at all seven Varsity locations. He was blown away with the results. Two news stations sent reporters, the event was covered online by the Atlanta Journal Constitution, and word spread on Facebook and Twitter. Sales catapulted roughly 3,000 percent, from 5,000 units per year to 15,000 per month.

“Free always works,” says Bonnie Riggs, a restaurant industry analyst at NPD Group. “That’s to generate trial, increase awareness, and remind people, if it’s not a new product, that they have this. It really is good at getting people in the store.”

Sales have been sustainable, fluctuating from 11,000–15,000 units per month, an anomaly in an industry where beverage sales are historically clunky, Muir says.

“On some days, sales are equal to or higher than Sprite,” says Muir, who now displays VO banners in the store. “It’s a historic menu item that’s been the core of the restaurant for all these years. People weren’t thinking about it because we weren’t making them aware of it.”