Martha Stewart's Tip For Turning Hot Coffee Into Iced, Without Cracking The Glass

Iced coffee makes getting through the heat of the summer bearable, but making it at home isn't as straightforward as putting ice in a glass and pouring hot coffee on top. Doing it that way will likely lead to your glass cracking, and maybe even shattering. The science behind this reaction is a process called thermal shock. When hot coffee hits cold glass, the inner surface expands while the outer surface remains contracted, creating stress along the structure. If the temperature difference is great enough, that stress can cause the glass to fracture or even shatter. 

Glass for everyday drinking use is rarely made to withstand abrupt temperature changes. Tempered or borosilicate glass can handle temperature extremes, but the tumblers in most cabinets won't. Pouring hot liquid into a cold glass is a shortcut that turns routine into risk. Shards scatter across the counter, the coffee's lost, and you have a tedious cleanup on your hands before you've even had your caffeine.

There are workarounds: Let the coffee cool, use a mug, or pick a sturdier vessel. But these add time, lose aesthetic points, or require equipment not everyone has. The problem isn't rare, and the solution doesn't need to be elaborate. Martha Stewart, whose kitchen advice is always equal parts practical and unpretentious, noticed the problem and suggested a simple fix: Just place a metal spoon in the glass before you add hot coffee.

The science behind the spoon trick, demonstrated by Martha Stewart in a recently reposted vintage clip on Instagram, uses the metal to conduct, absorb, and disperse some of the heat from the liquid. The brittle glass will warm more gradually, reducing the risk of cracking. The beauty of this approach is that it doesn't require practiced technique, specialty glassware, or extra equipment. The spoon is already in your drawer (although, Martha uses a silver spoon, naturally, for faster heat absorption). You should also avoid plastic, which can deform or leach chemicals when exposed to high heat.

Another hot tip for a colder coffee and a chilled glass is to try using cracked ice instead of cubes, which chills the glass more quickly and evenly. Also, if you want to keep your iced coffee cold without watering it down, freeze leftover coffee in an ice tray. Coffee cubes keep the drink strong as the ice melts. The spoon method is also useful when pouring hot tea or other liquids into a glass. Martha's simple adjustment could save you cleanup, wasted coffee, and more broken crockery.