Physical state of water at 80 degrees C on the upswing or downswing of boiling.

[BradP]

I have read that many tea masters insist that when infusing a tea that requires less-than-boiling water, you should first let the water reach a full 100 degrees C and let it cool back down to the target temperature, rather than take it off the burner as it is approaching boiling. I think it was called "breaking the seal" or something.

Could letting it reach a full boil really make a difference in the content (e.g. mineral profile) of the water? Or any other way? Just curious.

 

[LeonhardEuler]

Pure water at 80°C is the same regardless of its history of boiling, but if there are impurities in the water, boiling can have an effect. Any impurity that is more volatile (easy to vaporize) than water will be diluted, while less volatile impurities such as minerals will become more concentrated.

One other possible effect to keep in mind is that if you put a thermometer in a container of water and it reads 80°C, that is not necessarily the temperature everywhere in the container. If, for instance you heat a pot of water on a stove top and put the thermometer at the bottom of the pot, this is likely to be the hottest part of the water since heat needs to be transferred from the bottom of the pot to the top. Once liquid water starts to boil, the temperature reaches 100°C almost exactly, and pauses at that exact temperature for a while until all the liquid boils away. Because of this, the temperature becomes extremely uniform during boiling (or any phase change, like freezing as well). If the liquid cools down from the boiling point, it will probably have a much more uniform temperature distribution once it is measured at 80°C, since cooling will occur from all sides and be slower.
I'm not at all knowledgeable about tea, and I have no idea if this will actually have a noticeable effect on the taste of the tea, but it seems to be at least plausible. Someone would have to test it to be sure.

 

[Dr Lots-o'watts]

... actually have a noticeable effect on the taste of the tea, but it seems to be at least plausible. Someone would have to test it to be sure.

I would say this largely depends on the taster. Someone who drinks tea often and who is accustomed to a specific tea prepared a certain way, is more likely to be sensitive to small variations in the preparation, whether it's in the quality the water or the leafs.

But some tea drinkers also place great importance on the serving ritual itself, whether differences in taste are discernible or not. Like gardening or knitting, it's not necessarily about efficiency, logic and practicality.

 

[BradP]

Great points Euler. Thanks.