What changes when you cover the pot?
A lid changes how readily heat leaves the vessel. Compare covered and uncovered brewing without treating either method as a rule for every tea.
A small part with a noticeable effect
A lid looks like a minor accessory until you compare an open mug with a covered pot on a cool day. Covering the vessel generally helps retain heat during the infusion. This can make a familiar recipe more consistent, particularly if the room is chilly or the brewing time is several minutes. It is not a reason to ignore the tea's recommended water temperature at the start.
The lid can also collect condensation. When you lift it, keep the underside over the vessel or a drip dish rather than over your lap. A knob may become hot even if it looked comfortably cool a moment earlier. Use the handle or grip intended by the maker, and do not balance an unsuitable saucer precariously on a narrow mug simply to imitate a purpose-made lid.
Keep the rest of the brew the same
If you are curious about the difference, use the same tea, weighed portion and measured water in the same vessel on two occasions. Cover one infusion and leave the other uncovered. Keep the starting temperature and contact time as similar as possible, then taste at a comfortable drinking temperature. Otherwise you may prefer one cup mainly because it is cooler when you first try it.
Some brewing routines intentionally use an open bowl, while others rely on a lidded pot. Follow a recipe in its intended vessel before deciding it needs correction. A short infusion in a small gaiwan is a different process from a large mug left on the counter. The useful result of the comparison is knowing how your own equipment behaves, not declaring that all tea must always be covered.
The lid does not end the infusion
Once the tea has reached the strength you want, remove the leaves or decant the liquid. Putting the lid back on a pot that still contains leaves keeps both heat and continued extraction in play. If you want to hold finished tea warm, transfer it to a suitable clean vessel after straining. For herbal and fruit infusions, follow the full preparation directions, including boiling water and the specified minimum time; covering a lukewarm drink does not make up for starting it incorrectly.
