Illustration: Bratislav Milenkovic

The next great sports drink wasn't perfected on the field. In 2011 sports physiologist Allen Lim was hanging out in his friend's garage in Boulder, Colo., mixing together powdered ingredients—potassium, sodium, glucose, fructose, and various electrolytes—in paint buckets. "If you bought them from the local hardware store, they gave you lifetime free shaking on the machine," he says. "I doubt they knew I wasn't mixing paint." His mission was to package a healthy, effective alternative to mainstream syrupy options. "It's not just that those drinks have too much sugar," Lim says. "They have excess flavoring, coloring, preservatives, and vitamins—all those molecules contribute to gastrointestinal distress." (Gatorade, which has 80 percent of the market, disputes this idea and argues the sugar in its drink is "designed to provide fuel for athletes," says spokeswoman Lauren Burns.)

Lim worked much of the last decade for the Slipstream cycling team (now the Cannondale-Garmin Pro team) as its riders competed in the Tour de France. His job was to ensure the 25 cyclists were getting proper training, food, and liquids. "But their guts hurt," he says. "They were throwing up and getting cramps." He traced the issue back to the squad's go-to drink, a popular brand he won't disclose. He tested every other option on the market, all of which caused similar issues. "We tried cutting them with water," he says. "But then they weren't getting enough salt. So we added Alka-Seltzer tablets, which made it taste gross."

Then he started experimenting with homemade concoctions. He tested those on the team's top athletes, including Bradley Wiggins, who would go on to win the 2012 Tour. After a year of trial and error, the formula started working well, and cyclists from other teams began to ask for the secret swill, too. "I completely avoided our team sponsor's drink and would sneak Allen's into my water bottles," says Ted King, a professional cyclist.

At first, Lim made the product only for athletes who asked. Then, in 2010, sports drink company FRS—which sponsored Lance Armstrong at the time—offered to buy Lim out. As he mulled over the contract, a bird flew by and pooped on it. "I took that as an omen," he says.

Instead, he went into business with two partners, investing $200,000 to create a company, Skratch Labs, aimed at pros and more casually fit folks. "There are more people participating in things like running and bike races," says David Clucas, deputy editor of SNews, a trade publication that covers the industry.

That's given rise to boutique electrolyte drinks, most of which are sold in national groceries like Whole Foods and Kroger. No one tracks category sales yet, but the running retailer Fleet Feet says it sold about $900,000 worth of specialty sports drinks in 2014, and that number will increase to $1.1 million this year. Fifty-six percent of its sales are for beverages from Nuun, a company in Seattle that's seen 40 percent growth during the past two years and expects to take in $20 million in 2015. But Skratch Labs ($19.50 for 40 servings) is Fleet Feet's fastest-growing offering: In one year, it's swelled to about 10 percent of boutique drink sales. "People like the story behind how it was made. It tastes good, and it works," says Luke Rowe, vice president for business development at Fleet Feet. Skratch has expanded sales by more than 100 percent each year, earning just less than $5 million in 2014.

Unlike Gatorade, Powerade, and some other producers, Lim eschews colorings. He uses as little sugar as possible and incorporates more sodium citrate to better match the amount of salt we lose when we sweat. "When Gatorade was first formulated in the '60s, it was probably a lot like Skratch," he says. "But then they added sugar and color to sell it to the 7-Eleven crowd." Skratch is sold as a powder, for portability, and Lim also makes hydration mixes ($2 powder packets), including one geared toward efficiency-obsessed office workers.

Most scientists argue people get plenty of electrolytes from food, but that doesn't deter Lim. He says the sports drink demographic will only continue to grow. Lately he's received orders from the Atlanta Falcons, Boston Red Sox, and San Jose Sharks, even though they're sponsored by other drink manufacturers. And he had to move his operation into a 12,000-square-foot warehouse in downtown Boulder. "It's not glamorous," he says, "but it's a lot bigger than the garage."