Should a [Ceramic] mug be left covered or uncovered during the tea bag steeping process?

This seems like a case where a very simple A/B comparison will give you the answer for your own personal preference. Just use two identical mugs and do everything else the same except cover one and not the other. If you really want to make it official, put a mark on the bottom of one mug and then have someone else randomize them while you look away. (p.s. not sure why this question is getting negative votes, it seems fine to me).

Covering the mug may help insulate the tea/water, keeping it hotter. If you believe that a more consistent temperature produces a better cuppa, then covering would help (though how much is debatable). I'll leave it to someone else to provide arguments about the ideal steeping time and temperature.

Someone might also make a case that covering the mug keeps aromas trapped in too, but I doubt that does anything to improve the tea flavor, and your concentrated aromas are going to escape as soon as you take the cover off anyway.

So I'd say the insulation/heat conservation argument is where it's at.

Given that tea is 'properly' made in teapots, which always have lids that are put in place after the addition of water, I'd say you are wise to cover your mug. Insulation is probably the only advantage though, as bikeboy says.

I think this is purely one for personal preference. Try it and see.

If you have access to ISO (or I guess BSI or Indian national standards) there is an ISO standard for brewing tea for taste tests, which is moderately interesting.

I had a very fussy colleague train me in making him tea in a mug. It takes nowhere near 5 minutes.

• Put the teabag in the mug while the kettle is boiling
• Use the hottest water you can; it should go into the mug immediately after boiling
• Fill the mug almost to the brim; when you remove the teabag it will make room for milk
• It doesn't take long to get the best of the flavour out. 20 seconds or so; long enough to get the milk from the fridge and find a teaspoon.
• Fish the bag out with a teaspoon; maybe give it a squeeze against the inside wall of the mug
• add sugar (if wanted) then milk (if wanted)

With this method, the tea is still piping hot when it's ready.

If you prefer tea that's been steeped for ages, of course I won't stop you :). Please don't do it if you're making tea for me though!

You would steep for longer in a teapot, but that's because one normal teabag is enough for at least two mugs of tea -- unless you've bought special one-cup teabags, such as you get in hotel rooms.

This applies to ordinary tea and Earl Grey -- things could be different for fruit teas and green tea.

I think covering it only keeps it a little warmer and does nothing to change the flavor (that I've noticed), but in regards to the above comment about using boiling water to make your tea, I must, wholeheartedly, disagree. Black Tea should be brewed at 200°F and Green Tea at anywhere from 170°F-180°F (Although I prefer it at 190°F). I don't know of any tea that should be boiled unless you prefer your tea quite bitter.

So the only thing the lid does is keep the heat in and allows it to steep. I really won't steep much below 180 degree temperature. If it gets to room temperature it will stop the "steeping process".