Give tea leaves room to open
Compact leaves can occupy a surprising amount of room once wet. Check the space in the infuser, not just whether the dry portion fits.
The dry portion is only the beginning
A tightly rolled oolong can fit neatly into a small infuser and then open into a mass of large leaves. If those leaves become wedged together, water has less opportunity to move through the portion evenly. The outside may receive plenty of contact while the centre remains crowded. Adding more dry tea to compensate can make the same problem worse.
Look at the leaves after a brew. They do not need to float freely across an enormous pot, but they should not resemble a tightly compressed plug when you open the filter. A basket with a broad body often makes this easier than a small spherical infuser. Choose by the space available below the waterline, since a tall basket that is mostly above the tea does not offer much useful brewing room.
Change the container before the recipe
Try the same weighed portion, water volume and timing in a larger basket. Keep the tea fully immersed and allow a little space above the wet leaves. When the brewing time ends, lift the basket carefully onto a dish that can hold the drips. Compare the result after it has cooled enough to taste comfortably. You are testing the container, so avoid changing three recipe settings at once.
Brewing loose in a pot is another option if the spout filter can retain the leaves or you have a separate strainer. Check that you can empty the pot promptly. A roomy vessel loses its advantage if a blocked spout makes pouring take so long that the infusion becomes too strong. Very fine broken leaves may need a different mesh from broad whole leaves.
Leave room for cleaning too
A suitable filter should also be easy to empty. If wet leaves are packed into a narrow hinge or deep seam, cleaning becomes an unpleasant daily job. Let the equipment cool before handling it, remove the spent leaves, and rinse the places where particles collect. The best size is not necessarily the largest one for sale. It is the one that gives your usual portion room while fitting securely in the mug or pot you actually use.
