Thermodynamic ‘stones’ help keep coffee at the right temperature

Over 2.25 billion cups of coffee are consumed every day, with drinkers invariably finding themselves walking a fine line between “too hot” and “too cold.” Aiming to help make that middle ground last longer, Coffee Joulies are small stone-like devices that can be immersed in hot drinks — cooling them while they’re too hot, and then heating them as they cool down.