## Almost but not quite unlike tea

09.11.2009 16:00

On Saturday I bought some fancy Thé des Sables green tea in a new tea shop in Ljubljana. As explained by the friendly miss in the shop the French instructions on the bag say that it must be infused for 3 minutes in water at 75°C.

Unfortunately, I don't have a thermometer at hand that I would wish to stick into something I'm later going to drink. And even if I had one, I don't think I would bother to use it for each cup of tea.

So the question is, if I have boiling water from a kettle (obviously at 100°C) and cold tap water (let's say at 10°C), what's the perfect volumetric mixture to make the tea (i.e. something you can gauge by visual inspection alone)?

If T1 is the temperature of boiling water, T2 temperature of cold water, Tf desired final temperature, c specific heat capacity of water and m1 and m2 masses of boiling and cold parts of water respectively, then:

\Delta Q = \frac{(T_1-T_f)m_1}{c} = -\frac{(T_2-T_f)m_2}{c}
\frac{T_1-T_f}{T_f-T_2} = \frac{m_2}{m_1}

For temperatures I mentioned above, this gives mass (and volume) ratio of 0.38 or, in other words, a mixture of about a quarter cup of cold water and three quarters of boiling water.

There you have it, physics joins law and open source in service of a good cup of tea.

Posted by | Categories: Life

You also have to consider the temperature and material of your cup.

Consider it an exercise for the reader. I'm quite satisfied with a 10% error in temperature of my tea.

Posted by Tomaž

But back on the topic of tea, I've been at Le Palais des Thés and I had the impression that they've got the book smarts (the clerks there have to undertake some training), but lack in personal experience and taste.

Another grudge I hold against them is that they offer you a tea sample and tell you how it tastes like. Of course then your brain thinks it tastes like you're being told ...I want to *taste* my tea sample myself — being *told* the taste obsoletes any personal experience whatsover.

Well, considering it's a pretty new shop you can't blame them for the lack of experience. But yes, I know what you mean. I like Cha down the street better. It has less of that fancy imported feeling.

Although I must say I like the fact that they have dry samples of all their teas that you can smell before buying.

Posted by Tomaž