Fortunately, teas very rarely truly "expire." Even left out, tea can last for years and never (assuming it isn't left in a particularly moist environment.. mold and mildew can ruin any dry good) become dangerous to consume.. but that doesn't mean you'll want to consume it. When exposed to light and air for a long period of time, tea dries and begins to break down, leaving you with a stale-tasting, crumbly, weak mess.
You can always test a tea that has been left out and forgotten. Brew a small cup, depending on how long it has been out and your personal tastes you may find the tea to be perfectly fine. Even if it is drinkable, you will definitely be able to tell it is a bit old, especially in black teas.
|Tea tins on the counter|