These magical beans can keep your coffee hot for hours. Not blazing hot, burn your tongue on the first sip, and not disappointingly lukewarm, but coffee fit for every baby bear—just right. Genius.
But not really magic. The beans, called "Joulies" by inventors Dave & Dave, are made out of a metal phase-change-material inside a stainless steel shell. As soon as you drop Joulies into a boiling hot cup of coffee, the metal inside the beans melts, absorbing heat until your lovely liquid reaches a perfect 140 degrees Fahrenheit. It only takes a few seconds. As your perfect cup begins to cool, the metal inside the beans solidifies, releasing heat little by little, keeping the beverage warm for several hours.
The metal inside a Joulie is not special in its ability to absorb and release heat. Any substance that melts absorbs heat, and any substance that solidifies releases heat. The inventors used this well-known tenet of thermodynamics to fuel their invention.
The only downside of this seemingly wonderful modern coffee-lovers solution is that, although Joulies are shaped like a traditional coffee beans, they are actually much larger and so displace a lot of liquid in your cup. But, frankly, refilling your cup a few times is a small price to pay for perfect temperature coffee for hours.
The inventors Dave & Dave were neighbors and classmates in Pennington, NJ who engineered, prototyped, and hand-manufactured the first Joulies. They are now trying to raise money to manufacture their magic beans on Kickstarter; the project has been up for weeks now and has accumulated $89,000 in startup cash. If you support the idea, go donate.