How can I cool tea quickly?

What is wrong with a regular ice cube? As you state that the tea is not yet ready, you just use slightly less water and then add the ice cube, which has a fixed temperature.

I use this for large scale ice tea production. As I use 1:1 hot water : ice cubes I simply brew a double strong tea.

One solution would be to use Whiskey Stones. These are essentially stone (or metal) cubes that you normally use for whiskey to chill it without diluting it. This will also work for your tea

However, if this is a problem you run into regularly, you can freeze an ice tray with tea to make tea ice cubes and use that to cool down your tea. The main downside is, you would need to use the ice cubes on the same type of tea or it will affect the taste of the tea.

Possibly even easier than using ice or fridges or anything... pour it repeatedly from one container to another. Constant exposure to the air will rapidly cool the drink, you can get it to drinking temperature in less than a minute.

(Just make sure you pour accurately, or use larger containers. Spilling hot tea is no fun.)

Here's an example of a street vendor, who likes to be a show-off with this kind of thing. You can see him cool tea to drinking temperature in 10 seconds.

https://www.youtube.com/watch?v=-surEvJXj34

I do this everyday before I leave for work. I can't have really hot tea. So once my tea is ready:

1. I put it in a tea pan (a deep pan used to make tea). You can substitute with any other clean deep pan.
2. Add cold water to the kitchen sink
3. Stand the tea pan in the kitchen sink for 2-4 minutes

And I have the perfect temperature for my tea that suits me :)

You can always stand it in cold water for more or less time to suit you. And it does not affect the taste of the tea. I have tried to put the tea in the fridge before but it hasn't worked for me.

Pour the tea back and forth between two cups until the desired temperature.

Adjusting the height of pouring is fun to play with to get faster results but try it over a kitchen sink.

If you'd love to bring a gadget into play:

Many parents use a "Cool Twister" to quickly bring the water for baby bottles from boiling to a choosen temperature in less than 90 seconds. You could also run your tea through it and cool it down - or parts of it.

The manufacturer suggests the use for tea and coffee on his website as well:

Can the Cool Twister also cool down coffee or tea? Basically yes. The temperature can be chosen individually between approx. 40 and 80° C. [...]

Boring but effective: brew, pour and sugar/cream as usual; when teacup/mug is hot to the touch, transfer to fresh cup.

make a concentrated infusion (same amount of tea less (boiling) water). When finished fill up with cold water.

I put a silver spoon in the tea. It makes the spoon extremely hot very quickly, but the silver spoon will take the heat. Careful when removing the spoon as it will be hotter than you imagine!

The system I use at my office desk is this: I have a small aluminum soda can (7.5 oz size) that I keep about an inch and a half of water in. I leave about 1.75" of empty space from the top of my mug. Once the tea is made and infused, I simply float the can in the tea for a bit. This pulls out just enough heat to make the tea pleasantly hot with no mouth burning.

(Note: Don't forget to clean the can and change the water so the water doesn't get nasty.)

A saucer was invented for that purpose (to accompany cups with a handle). Pour hot tea into saucer using the handle provided and slowly drink off from a point on its edge while raising the diametrically opposite point.

Stirring with any metal spoon will rapidly cool the tea, as the metal will absorb the heat. Silver, as suggested, is a good conductor, but any metal will do.

According to Physics.SE (and graciously cited by XKCD What-If), dipping the spoon in and out is slightly faster, though not by a highly significant value, and stirring or simply doing nothing will still get similar results.

Note that while you could use the results of that first link to time your own tea-cooling, I would recommend timing it yourself in your own environment, since the temperature and air pressure is likely to be different for you wherever you drink tea.

Shake it up (in a cocktail shaker?) with ice cubes then pour it out again through a strainer. This is how I make iced tea in summer. Obviously you shake it a bit longer for iced tea!

If you like to sugar your tea, you can replace the sugar by honey. It's better to me (but it also depends on your taste ^^).

Enjoy your tea !