Credo non ci sia un procedimento particolare ma ho trovato questi due testi
Clay comes from the earth and is thought to play an active role in the process of brewing green tea in Japan. Think of clay as living, organic material that influences the brewing process – good quality clay creates a positive, dynamic, alchemical interaction with the brewing green tea. Its mineral composition has an alkaline effect on brewed tea, and naturally enhances a sweetness that is present in the tea, which results in a desirable favour. Sweet and bitter flavour combinations are particularly appreciated within Japanese cuisine.
The length of time that a teapot remains hot is dependant on the weight and thickness of its clay. Tokoname clay is especially fine and thin; therefore it does not retain heat for long durations, which is ideal for green tea as it requires a relatively low water temperature for brewing. If the Kyusu retained heat for too long, it could over-heat the tea causing an undesirable change in flavour.
The porous nature of clay allows for greater oxygenation during brewing which enhances the flavour of the tea, while seasoning the Kyusu after multiple uses. The flavour of your tea will linger, trapped within the porous clay. It is best to use one type of tea in your Kyusu, to season the interior with the same flavour, and to avoid confusing your palate. The more the Kyusu is used, the better and more unique to the owner it becomes; a functioning record of use and enjoyment.
When it comes to teapots made of unglazed clay, it seems to be the general consensus that one should stick to one type of tea, if not one specific tea.
The idea is that the clay absorbs tea extracts and therefore some of the tea's aromas and flavors will be absorbed by the clay as well. From what I have read, this "seasoning" can have a positive impact on the tea with certain types of tea.
This thread is specifically about sencha and Tokoname clay tea pots. What I am saying may not apply to other types of teas or other types of clay, on which my knowledge is very limited.
When I was new to using clay teapots, this was the rule I followed.
I got two reduction fired Tokoname-yaki clay teapots by Sekiryu and used them strictly for Japanese green tea. To be exact, I used them for a lot of fukamushi and asamushi, some kabusecha and very little gyokuro (negligible amount) as well. Nothing flavored, scented, roasted or mixed with other ingredients, just plain sencha.
What I normally do to clean a kyusu is to remove the used tea leaves, rinse the pot with water a couple of times and use a toothbrush to make sure all leaf particles are gone from the teapot and from the filter. Then I use a small bottle brush to scrub the inside of the spout. Finally when the teapot is already "clean", I fill the pot with boiling water, let it sit for about a minute, and pour it out. Then I let the teapot dry with the lid off. I do all of this shortly after each use. I do not let the used leaves sit in the teapot for hours when I'm done drinking tea.
I think this is a pretty normal cleaning routine and it may even be more thorough than what some do for daily use.
So, after using these teapots very regularly (at least once a day) I noticed that the hot water I passed through the kyusu in order to preheat it had an unpleasant smell to it. I proceeded to taste this water and sure enough, the taste was unpleasant as well.
I am not talking about the "iron" taste that the water gets from the clay, which is not unpleasant at all, I am talking about a bad, kind of foul taste and smell. I figured that this must come from the tea residue or patina which accumulated on the surface of the teapot's inside.
Luckily I had a brand new Tokoname shiboridashi to compare these findings with. Sure enough, the water smelled better, it tasted better. More importantly, the tea tasted better. Don't get me wrong, it's not that the tea from the used kyusu tasted bad. Had I not noticed the smell in the water I used to preheat the kyusu, I had probably not noticed that there was anything "wrong". Still, that underlying smell and taste definitely had a noticeably negative impact on the tea that was brewed in the used kyusu.
So recently, I gave my my most frequently used Tokoname kyusu a thorough cleaning.
First, I soaked the kyusu in warm water for a couple of hours. I figured this could not be a bad idea. Now I think it's probably not a necessary step.
Then, I put about a tea spoon of baking soda (sodium hydrogen carbonate) inside the teapot, added a couple of drops of water to create a paste. After that, I thoroughly scrubbed the inside of the kyusu with a toothbrush, using the baking soda paste.
Shortly after I started scrubbing, the paste started to turn a brownish red and I realized the tea stains started to rub off.
When I was done scrubbing, I rinsed the teapot and proceeded to wipe the inside with a wet microfiber cloth. The cloth turned a brownish red as well so clearly, I wasn't done cleaning. I continued cleaning until nearly no more rusty red rubbed off on the cloth.
Then I rinsed the kyusu with boiling water and let it dry, curious to see how clean it would be when it was dry. I was quite impressed with the results.
Not only did the kyusu look significantly cleaner. After the cleaning, the "foul" taste and smell were gone, and the tea simply tasted better than before the cleaning.
Therefore, I have come to the conclusion that an unglazed clay kyusu that is being used for Japanese green tea needs a thorough cleaning from time to time.