The sidewalk sign says “16 steps to better coffee,” which is true enough. But you’ll need to walk a few more paces — past the glass-covered pastries, past the cash register, past the espresso machine — to reach the true heart of Sweet Science Coffee in Adams Morgan.

It’s a section in the back of the subterranean shop. Proprietor Sandra Wolter calls the space her “slow-brew bar.” It’s a counter where Wolter will use one of her many gadgets to brew, arguably, the finest, most balanced cup of coffee in the District. But the counter is also where Wolter will share, if you’re interested, a tiny fraction of the coffee wisdom she has accumulated over four-plus decades.

Now, I know what you’re thinking: Wolter must be one of those insufferable geeks who complains about the dark-roast blends at Charbucks while sipping a fruity, $8 cup of specialty coffee extracted from naturally processed beans purchased from some remote farm high in the Andes.

Relax, she’s not that kind of coffee geek.

Wolter, in fact, has developed a “passion statement,” which concludes with an acronym, the official code language of Washington. “It is all about HCOC,” the statement reads on the shop’s website. “Human Contact Over Coffee. We are passionate about preserving this value for the future.”

This is what separates Sweet Science Coffee from the rest: It’s a shop firmly committed to specialty coffee and all the gadgetry that comes with it. But it’s also aligned with the spirit of old coffee­houses, where a cup of mud was an excuse to gather and talk, not log on to the free WiFi for the afternoon.

Sweet Science is a partnership between Wolter and the Popal Group, the family-run company that operates Lapis, the Afghan restaurant above the coffee shop. The Popal family covers the rent and labor costs. Wolter supplies all the coffee and equipment, which is extensive. She has a La Marzocco espresso machine, a Mahlkönig EK43 grinder, Japanese cold-brew towers and seemingly every brewing device ever created, including a Karlsbad porcelain brewer that uses no filter whatsoever.

For a shop buried in a basement, with little natural light other than the sun that illuminates the stairwell, the space feels open and inviting. It’s partly because of the whitewash walls, but the room itself has a comfortable, lived-in ambiance, with mismatched chairs, fireplace facades, oversize mirrors, large Afghan rugs and a communal table in back, by the slow-brew bar. The space feels like home, or at least home away from home.

At 46, Wolter has been around long enough to see the evolution of the coffee business. She worked at her family’s cafe and roastery for six years in Germany, eventually switching to a TV reporter job for more than a decade. Even as a journalist, she never lost touch with the coffee scene.

After her mother died, in 2013, Wolter wanted a fresh start. She found it two years later when she moved to Washington to launch her Sweet Science Coffee pop-up at its first Adams Morgan location. Her shop lasted only a year, the result of a rent dispute with her landlord.

Her current agreement with the Popal family is only a temporary, six-month arrangement, which began in February, to see how the experiment pans out. “I’d like to stay and make it work,” she says. “I would definitely like to have my own shop, too.”

A large part of Wolter’s vision for Sweet Science is to provide a space for tightly wound Washingtonians to decompress. The baristas under her watch can pull a mean espresso and prepare any number of espresso-based drinks. Sweet Science also has its own custom blend, Pivotal Moment from Brio Coffeeworks in Vermont. The sweet, chocolate-y blend, with a touch of lemon brightness, is available as drip coffee. There are even biscotti, muffins, biscuits and croissants made by Ruth Stolzfus, pastry chef for the Popal Group. Prices range from $1.50 to $8.

But the place to be is the slow-brew bar, which allows you to literally stop and smell the coffee. Beans from such roasters as Commonwealth Coffee, Ruby Coffee or Ceremony Coffee are placed in small jars, which you can open and sniff to see which one appeals to you. Wolter dials in a recipe for every bean on the bar, relying on a different brewing device for each. She, for instance, uses a Kalita Wave to brew the honey-processed beans from Costa Rica and relies on a siphon to brew the Rwanda Twumba beans. The wait is part of the deal.

“You can take those 10 minutes for the pour-over . . . to free your mind and free your thoughts for a moment,” Wolter says. “And get more ideas!”

For your pour-over, Wolter may pull out her notebook in which she has written precise, step-by-step instructions for each coffee, down to how many grams of water to pour for every pass over the grounds. Each time I visit Sweet Science, I learn something about coffee and brewing. Better yet, I walk away with a coffee of unusual complexity, like a recent cup of Kenya Gondo AB from Ruby with its bracing citrus acidity that cuts through the sweetness.

As a barista dedicated to science, Wolter has been conducting an experiment at her new location. She’s keeping a log of every slow-brew customer. She wants to find out how many treat the shop as an office, squatting with their laptops for hours, and how many consider it a communal space or library, where they can pull a book from the shelves in back.

The results?

Between 80 and 90 percent of the slow-brew customers do not bring a laptop and surf the Web. Those types are not the serial squatters at Sweet Science.

“They either read or meet friends,” Wolter says, “and they tend to share the coffee.”

Sweet Science Coffee, 1847 Columbia Rd. NW, 202-344-5639.

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