The unfurling of tea leaves during steeping.
When tea leaves are harvested and dried, they curl or shrivel and remain in that state until hot water is used to brew the tea. As the leaves unfurl, they can be seen to ‘convulse’ from the re-hydration process, looking like they’re in agony – hence the term. This process is only seen with loose tea leaves, not in bagged teas.
This is an expression used by the tea trade referencing the unfolding or unfurling of tea leaves in hot water. It is an interesting thing to observe especially those specialty teas that have been rolled or twisted such as jasmine pearl or an oolong, for example. One important thing is to allow enough room for the tea leaves to unfurl in order to brew properly.
This is why you should use an infuser (basket, ball, or tea sack) that is at least twice the size of the amount of tea you will be using, allowing plenty of room for the tea leaves to unfurl. Or simply add loose tea to the bottom of your cup, depending on your steeping and serving style or traditional practice. Another reason pyramid shape tea bags have become so popular – these give more space for specialty, loose leaf/full leaf teas to fully open during steeping.