What weighs less than a penny, is smaller than a strawberry, but bold enough to give even the most adventurous of beer drinkers pause?

The Dogfish danger cap, that's what.

If you've ever had a bottle of World Wide Stout, 120 Minute IPA, Fort or Olde School Barleywine, you've popped the cautionary exclamation shark, but what you might not know is how exactly that little yellow and black cap came about.

"It's definitely one of the most distinct caps out there," says Dogfish Head purchasing guru Chad Collier, "but it wasn't originally a design thing."

All Dogfish beers over 15% ABV get a yellow and black danger cap.

Turns out the danger cap was more function than fashion, and we owe it all to World Wide Stout and a few plucky beer buyers. Back in the late '90s, World Wide Stout was the most potent beer on the planet. The ridiculous amount of barley and the time it takes to brew World Wide mean it's a little pricier than your average 12-ounce bottle of beer.

But here's the rub: The label and copper cap on World Wide Stout looked a lot like the label and copper cap on our much more down-to-Earth Indian Brown Ale, especially since neither has a neck label. A few bold – some would say unethical – beer buyers were taking bottles of Indian Brown out of their six-packs and replacing them with World Wides. Most retailers were none-the-wiser and ended up on the losing end of this creative transaction.

World Wide and Indian Brown separated at birth? The danger cap tells the tale.

"The barcode on the carriers would still scan as Indian Brown," says Dogfish Head Founder and President Sam Calagione, "so we created a very bright, noticeable cap so retailers would know that these beers are to be sold individually and not hidden in 4-packs or 6-packs."

The caps were a natural fit for our other high-alcohol beers, so each beer we brew over 15% ABV now gets its own little yield sign. Beers between 9% and 14% get a red cap – or crown, in beer industry lingo – and beers below 9% ABV get a copper cap. Palo Santo Marron – our year-round, wood-aged brown ale – gets its own wood-grain crown.

Once in a great while, a rogue danger cap will slip through and get crimped onto a bottle of beer under 15% ABV, but it rarely makes it out the door.

"We usually notice anything that's off," says Eddie Atkins, Dogfish Head's packaging line lead. "They're not hard to spot when you're looking at a sea of red or copper."

Caps of all stripes are relatively inexpensive, but play a priceless role in freshness. "They're the least expensive piece of critical quality we run on that line," says Chad. "A kinked cap can shut down the bottling line for hours."

Over the years, we've seen some pretty creative uses for danger caps: magnets, mosaics, earrings and checkers. But these days, their raison d'être is to remind Dogfish supporters to go easy on our biggest beers.

"When you see a danger cap," Sam says, "you know it's time to sip, share and savor."