Tea water thermocontrol

Some teas are best brewed with water of a certain temperature. Like green tea, which the recommendation is to brew with water that is 75-80°C. But not everyone has an electrical kettle with temperature control, or want the bother of having one. That is fine, they can use this method instead.

1. Add the tea to your teapot. It can be in a bag, if that is what you prefer.
2. Add a measured amount of cold tap water.
3. Fill up with freshly boiled water from your electrical kettle.
4. Let steep.

For this method to work, it requires that:

• You fill your teapot to the same level every time.
• You have gone through the measuring and calculating, to figure out the right amount of cold water to add in step 2. You only do that once in the life of the teapot.

To calculate the amount of cold water by hand, you start by determining what values the four parameters have.
t_c: temperature of cold water
t_h: temperature of hot water
v: volume of tea water
t_t: target temperature of tea water

Then you plug them into this formula, and do the calculation:

v_c = v·(t_h - t_t) / (t_h - t_c)

The formula is derived this way...

The temperature of the tea water is: t_t = (v_c·t_c + v_h·t_h) / v , where v_h is the volume of hot water

Getting rid of v_h gives: t_t = (v_c·t_c + (v - v_c)·t_h) / v

Simplifying gives: t_t = (v·t_h - v_c·(t_h - t_c)) / v

Isolating v_c gives: v_c = v·(t_h - t_t) / (t_h - t_c) QED