The Interesting Reasons To-Go Coffee Cups Have That Extra Teeny Hole

Starbucks alone goes through about 7 billion disposable cups every year, according to CNBC. Every one of its hot beverage cups has a tiny little hole in the top that most of us never think twice about. Despite what you may have heard, that little hole on your to-go coffee cup lid is not just a product of manufacturing, nor is it there to let you experience aromas better — but it's not useless either. In fact, this design feature has several important functions that allow you to enjoy your coffee safely and conveniently.

First and foremost, that small hole allows steam to escape. If a lid is fully sealed right after the cup is filled, steam can gather inside. Under the right conditions, that could build enough pressure to pop the lid off and result in a nasty burn. Letting a tiny bit of steam escape instead makes that pressure build up less likely to happen.

The other benefit of that hole relates to a balance of pressure and airflow while drinking. Some readers may remember those vintage soda cans with two press button holes on the top that needed to be pushed in by hand. One hole was for designed for drinking, while the other performed the same function as a tiny coffee lid hole. Without proper airflow, liquid doesn't pour out smoothly and causes pressure to build. When you stop drinking and remove your mouth, airflow returns and relieves pressure, which can cause liquid to rush toward the opening and spill in the absence of this extra hole.

To see for yourself what happens when pressure isn't equalized, fill a coffee cup with a cool liquid and then cover the hole up with your finger. Now try to pour your liquid out. Instead of pouring smoothly, it will suffer from negative pressure and glug out rhythmically. For room temperature liquids this is just an inconvenience, but for hot liquids it can be dangerous as the inconsistent flow could lead to splashing.

Something you also may not have considered before is how the heat of your macchiato or latte could damage the lid. You might simply expect the lid on your warm beverage to be able to handle hot liquids, but without that little vent on top, steam can cause it to warp. A warped lid, or one that's starting to melt, is another safety hazard that could lead to accidents or burns while you're drinking.

That tiny hole on top of a coffee lid also ensures a more pleasant drinking experience. Any size would allow steam to escape and air to flow so that the liquid pours out smoothly. However, a larger hole in the lid could lead to extra spills and mess, as well as poor temperature control. If the hole was bigger, your coffee would cool more quickly. There was some precision engineering that had to go into determining the exact right size for that hole so that it could give you all of the benefits and none of the drawbacks of a larger hole. That's pretty impressive for such an insignificant-looking thing. So next time you order your favorite hot drink from Starbucks (or any chain for that matter), take a moment to appreciate all the help that little hole in the lid is providing.