If you buy a bag of whole bean coffee at the cultish third-wave coffee shop Blue Bottle and ask the barista to grind it for you, he will say, “Sorry, we don’t do that,” or some variation thereof. You might be surrounded by coffee grinders. One for the company’s Bella Donovan blend. Another for the Ethiopia Hambela Estate Buka. Grinders nearly pouring from the rafters. And there you are, staring slackjawed as the barista gently explains that to preserve the coffee’s quality, you should grind the beans yourself at home. Blue Bottle won’t touch them. As a matter of policy.

Today the VC-backed, Oakland-based chain is debuting a new product: ground coffee.

Called Blue Bottle Perfectly Ground, it’s prepackaged, single-serving ground coffee that will be sold at Blue Bottle’s shops, online, and in Whole Foods alongside the likes of Illy and Peets. Each packet is ground for a specific production method (such as pour over or French press), includes detailed instructions on how to make a perfect cup, and has the sleek white and blue design that has become a Blue Bottle calling card. Packets cost $3.50 each or $17.50 for a box of five.

To those who prize Blue Bottle for its unflappable–some might say fascist–commitment to coffee purity, Perfectly Ground might seem like a terrible idea. Another company chasing the Starbucks dream. James Freeman, the shamanic CEO who started Blue Bottle by roasting beans in a 183-square-foot potting shed in Berkeley, California, wasn’t even sold. He had spent 14 years vowing to never sell beans more than 48 hours out of the roaster. But Freeman was persuaded by Neil Day, a serial entrepreneur who tinkered with engineering problems in his spare time and developed what Freeman calls an “uncompromised way of selling ground coffee.”

The secret is a warehouse in Belmont, California, that Blue Bottle employees enigmatically dub “the dome.” Roasted coffee beans start to go stale when they’re exposed to oxygen. That’s why the decaf Folgers in the back of your cabinet tastes like coffin dirt (and why Blue Bottle baristas won’t grind beans for you). The dome provides a zero-oxygen environment for Blue Bottle to grind beans to the perfect grain, then pour the grounds into airtight plastic packages, effectively locking in the flavor.

There are no public photos of the dome. And Blue Bottle is annoyingly tight-lipped about exactly how it works; like so much in Silicon Valley, the technology behind it is “proprietary.” Day, who has done stints at Shutterfly, Apple, and Sears, developed the technology for the dome at nights and on weekends–a “hobby run horribly amok,” he says. He tested it with coffee from other companies but felt that if he could convince Blue Bottle–and its exacting CEO–he had created something of real value. Many (many) taste tests later, Freeman got on board. Blue Bottle acquired Day’s company in 2015.

I blind-tested Perfectly Ground and coffee from freshly ground beans at Blue Bottle’s light-filled cupping room in Oakland last week, and I couldn’t tell them apart. Mind you, I am not a discerning coffee drinker. Anything is fine as long as it doesn’t come from a gas station, and even then . . . I also had the early stirrings of a cold. But I still had taste buds. And neither sample tasted bad. For prepackaged ground coffee, that is a feat.