h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Due to the (semi)heatwave in recent days, I thought I'd try my hand at making iced tea. Instead of going to all the trouble of boiling water, making tea, then pouring it over ice, I decided to save myself time by just putting the tea leaves in cold water. Having done so, I wandered off, and came back in about five minutes' time to find the tea leaves sitting placidly at the bottom of a completely colourless cup of water. I am sure there is a perfectly good reason for all this, but neither I nor my scientifically inclined friends can come up with one (the best suggestion so far has been that hot water is needed to break down some sort of coating on the tea, but we can't find anywhere to verify this). Any thoughts would be appreciated as we are perplexed.

Well, I think when you boil tea you're doing 2 possible things

1) dissolving chemicals in the tea leaves into the water
2) causing those chemicals to undergo reactions

Rates of chemical reactions depend strongly on temperature. One rule of thumb is that around room temperature, "typical" rates (relevant to bio and organic) can double for every 10 degree increase in temperature

The change in temperature between 20 and 100 C is 80 C -> that would be a factor of 2 raised to the 8 power change in the rate of reaction or 256. So *in theory* if it takes 1 minute to make tea with boiling water, it would take 256 minutes with room temperature water (~6.25 hours).

To make the best cup of tea you always have the water boiling as it is poured over the tea leaves. As opposed to coffee when you're meant to let it come off the boil a bit...not sure why .

But you *can* make iced tea with cold water: A793659

It's pretty good, too. I've made it several times

Aha, you have to leave it overnight. The reaction time must be the thing, then. Thanks!

Ah, you got there before me, broe

The principle is the same for tea or coffee - cold brewing takes much longer but tastes much better.

These are interesting sites

http://www.silentliontea.co.uk/info+articles+tea-preparation.html

http://www.teatalk.com/

Tastes better, Gosho? I can't agree - tea must be made with boiling water - letting it stew in warm water just isn't the same.

It depends on the tea and the method, B. 'Stewing' suggests heat, but cold brewing is done with cold water and in the fridge. I guess it doesn't really need to be done in the fridge but that's where it usually goes because it's being made for iced tea/coffee and you might as well cool it down anyway I guess. You could probably do it at room temperature with successful results.

We use hot water to make tea and coffee only because it's quick, but hot water extracts some of the more unpleasant flavours from the leaves/beans too if not brewed carefully. Cold brewing doesn't do that but it takes much longer. And it doesn't get stewed. We all know the taste of stewed tea You don't get that taste with cold-brew because the chemicals that produce it can only be extracted by hot water, as far as I know.

There's a brand of cold brew coffee-maker here which is silly enough to publish the method on its website http://www.toddycafe.com/customerservice/instructions.php meaning that we can use this method at work to make our iced coffee but with the regular coffee filters and a jug. I've tried it at home too, cold-brewing the coffee concentrate and then adding boiling water to it to make a cup of hot coffee. It's quite delicious, but as I don't drink a whole lot of coffee, and when I do I hot-brew it well enough that it doesn't taste bitter, it's more of a chore than it's worth. I just brew fresh-ground drip coffee whenever I fancy a cup.

Another option is sun tea, but you guys in the British Isles don't get enough sun to do it properly. You get a big jar (a gallon or two), fill it with cold water, add some teabags, and stick it outdoors somewhere that it'll get a lot of sun. Leave it there all day, and you have a refreshing, bitter-free tea with dinner.

I tried making cold-water tea overnight there, and it's delicious! So the fridge is now full of plastic containers with different concoctions brewing. I'm particularly looking forward to iced Earl Grey and lemon.

Well, I've been inspired! I think I'll give the Earl Grey a go meself today!

I recommend Darjeeling too.

Earl Grey tea is an abomination sayeth the Lord!

And I don't care for it much either

Assam or Darjeeling are the best for making iced tea, I find.

Assam? Really? I wouldn't have imagined it would work well but I might well try it since I have some knocking about .

I suppose hot water brews tea a little faster because the heat creates convection currents, allowing it to mix more. Though I should think that effect is only very slight.

I've just put some loose tea in a jug and bunged it in the fridge. I gave it a stir around so it didn't just float on top. But then I noticed that the tea seemed to separate. So now I have a layer of tea leaves floating on the surface and a layer at the bottom of the jug. There are a few bits in between which are slowly floating...well, both up and down. Not the same bits, you understand. But while one leaf is floating up, another is floating down. They appear to be separating.

I can't really think why this is. Something to do with surface tension, perhaps?

Assam is good for iced tea because it's got plenty of flavour and strength, like Darjeeling and the better quality Ceylon teas. Weak or subtle types of tea make an insipid iced tea that's about as interesting as drinking water... and tastes like it too.

Iaconian - hot water extracts the flavour from tea leaves and coffee grounds much more quickly than cold. That (and the fact that we like to drink tea and coffee hot) is the main reason we boil water to make tea or coffee. But it also extracts more of the flavours we don't want, which is why there's such an art to brewing hot tea or coffee.

No idea why your tea's doing that, Ioconian. I put mine in one of those infuser things (is that the proper word? I just took a complete mental blank) so it didn't happen.

And I don't like Earl Grey on its own, but it's incredibly good with vanilla (and lemon, if I'm feeling exotic).

I wonder if there's a H2G2 Tea Club yet.