When you get married, you register for a lot of stupid shit. That’s why I currently own a cast iron tortilla press, a stainless steel turkey lifter, some five-blade herb shears and a silicone honey dipper. One of the more aspirant items I registered for was a crystal decanter, imagining at the time that I’d fill it with good Scotch and keep it on a cart in my office to serve visitors.

Instead, for the first year, it remained completely empty, gathering dust and cat hair. But recently I began to use it as a sort of whiskey waste bin. Whenever I had a few ounces left in a bottle and wanted to clear shelf space, I’d pour it into the decanter. I was, it turns out, inadvertently creating my very own “infinity bottle”—a personal history blend that’s become all the rage among whiskey nerds.

The infinity bottle (or “fractional bottle” or “living bottle”) seems to have first entered prominence courtesy of a 2012 video by popular whiskey YouTuber Ralfy Mitchell. In his thick brogue, he rhetorically asks viewers, “How can you create something which is 100 percent uniquely yours? That is part of your whiskey or spirit drinking history? That becomes, in fact, a family heirloom in time?”

His answer is what he calls a “solera bottle,” likening his experiment to the world of sherry, in which casks are fractionally blended over time via the solera system in order to create consistency. Using an empty bottle from WhiskyBlender, Mitchell affixed a label to the back in order to keep a running tally of each new whiskey he added, and when. An infinity bottle, he says, can create “a taste that you just can’t buy,” one worth far more than what he paid for the component whiskeys. He also imagines a world where children inherit their parents’ or grandparents’ solera bottle started decades before.

Helmut Barro, a German cocktail blogger, was inspired by Mitchell. His infinity bottle began in 2015 with some Four Roses Yellow Label followed by Ben Bracken 12 Year Single Malt Scotch, then Rittenhouse Rye.

“I began to appreciate the work of professional blenders and how difficult it is to keep up a continuous taste experience for a customer,” he explains. “With each new addition [to my infinity bottle], the taste actually changes—sometimes to the good, sometimes to the weird.”

Some people, like Mitchell, are methodical about how they build their bottles, tweaking and testing before adding each new pour. Others choose to live dangerously, tossing the final ounces of any and every bottle into their mix, just to see what happens.

“The flavor changes pretty heavily over the years,” notes Reddit user “robotsongs” (he asked that I not use his real name), who pours a shot of every single malt he’s ever purchased into a Balvenie bottle that’s had its label removed and an infinity symbol painted on the front—courtesy his wife’s gold glitter nail polish. “Sometimes it’s unfocused and fuzzy, sometimes it’s goddamn on point. But no one will ever try that bottle besides me and my friends and it’s a fun and easy project.”

Most all discussion of infinity bottles today is relegated to online message boards, mainly Reddit, under discussion topics like:

“Recommendation for a starter solera?”

“Infinity bottle – do’s and don’ts”

“Infinity bottles…your thoughts/experiences”

According to most posters, the rules of infinity bottles are yours to write. Some people think you should only use the same style of whiskey—that is, if you start with a bourbon, stick to mixing it with other bourbons. Others, myself included, believe that mixing and matching—throwing bourbon, rye, Japanese whisky and Scotch all in the same bottle—is what makes these infinities interesting.

“I keep records of each mix because they are never quite what I expect,” explains another forum poster from Wisconsin. “Wasmund’s [a Virginia whiskey] and Ardbeg taste like bubblegum.”

Though whiskey—if not Scotch—is most frequently used, it’s not the only spirit that’s been subject to the infinity treatment. In fact, many believe Cognac is actually best for infinity purposes. And experiments with both rum and gin have popped up in these message board discussions.

Beyond of the confines of Reddit, the infinity bottle has become something of a handshake among acquainted whiskey enthusiasts. Offering a taste from one’s very own infinity blend is a gesture of hospitality that’s more personal than pouring out, say, a taste of Yamazaki 18 or Pappy. After all, a geek’s most cherished bottle is often his or her own blend. “I must confess I am a bit afraid to add other spirits to my rather long-running whiskey solera, as I don’t want to ruin it,” says Barro. “I’m emotionally attached to it by now.”