Why do coffee/hot beverage lids have a little hole on the top part? What is its purpose?

Why do coffee/hot beverage lids have a little hole on the top part? What is its purpose?

You can check the answer of the people under the question at Quora “skinny brew coffee pyramid scheme

0 thoughts on “Why do coffee/hot beverage lids have a little hole on the top part? What is its purpose?”

  1. Corey and Trip have provided the correct answers, but you could have also discovered the answer by the simple expedient of covering the hole tightly with your finger and observing the results, thus making it a teachable moment 🙂

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  2. There’s really only one reason.
    It’s to let air in when you drink. When you take sip, do you ever notice the whistling sound? That’s air being pulled into the through that tiny hole. You’re removing liquid from that container. For the pressure in the cup to stay the same, you need to replace that volume. If you try putting a piece of tape over the hole and take a drink (not with coffee hot enough to burn you or cloths you don’t want coffee on) you’ll find it doesn’t go as smoothly. You might even cause the cup to collapse inward. Spills are also a lot more likely.
    The hole does not to help to let out steam. Hot coffee does not continuously produce steam unless you’re heating it continuously as well. Besides, there’s already much bigger hole that would provide that.
    The closest thing to the idea of escaping steam happens when you first put the cup on. Air that was previously exchanging with the room is not trapped under the lid. As it warms up, it expands. If the lid was a perfect seal and had no holes at all, it just might pop back off, but that’s a one time expansion as the air warms, and not a continuous source of escaping gas. Conversely, as the coffee cools, there’s a contraction. Again, the drink hole would take care of that just fine by itself.
    If you ever use a travel mug, you might notice that the first time you open it, it’s under positive pressure because of the heated air inside. If you then close it and let it sit a while, the next time you open it, it’s under negative pressure because the hot air has now cooled some.

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  3. It serves two purposes, both based on simple physics. If you take a sealed container of liquid, and only put one hole in it, the liquid cannot be poured from the container smoothly, the liquid will bubble and splash – an undesirable behavior in a hot liquid you are attemping drink – because air is entering the container (to fill the space displaced by the liquid) through the same hole the liquid is exiting from.
    Similarly, the top acts as an insulator for the heat from the beverage. If the spout on the top is sealed, the steam produced by the hot liquid needs to escape, or risk melting the top, or dislodging it from the cup from the steam pressure – which causes more spills and burns. Its the same reason you should avoid putting steaming hot coffee in a sealed, insulated thermos without letting it cool first.

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  4. Good answers above. I always use the point of one of my keys to poke that hole a little bigger, which makes the drink flow smoother and faster. Some batches of the lid also have an imperfect hole which doesn’t let enough air in.

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