The taste of water differs depending on how tetsubin is made

Many people are aware that a tetsubin effects the taste of water by making it smoother. But, do you know that different brands or different manufacturing method affects the taste remarkably too? I’ve carried out the following experiment to verify the effects of the taste between the different manufacturing processes.

Kamayaki process that affects the performance of a tetsubin

Tetsubin is a cast iron kettle where melted iron is poured into a mold which carries a distinctive design created by the manufacturer. After the casting, the tetsubin is in white-silver color and the tetsubin in this condition gets rusty easily. Thus, the tetsubin is then baked with charcoal fire. This process is called “Kamayaki” which means “firing in a pot”. The term pot refers to a small open kiln. The objective of Kamayaki is to reduce the surface of tetsubin which would prevent it from rusting. The charcoal fire is an unsaturated fire; when the surface of tetsubin is reduced, it will turn into a dark blue color. This process affects the taste a lot. I have requested the tetsubin manufacturer to produce a tetsubin according to my parameter and study the relationship with the taste of water.

1. Tetsubin without Kamayaki
2. Tetsubin with twice as long Kamayaki as standard

I have compared the taste of water boiled in the above tetsubin versus a normal tetsubin. We used hard charcoal for the experiment.

The results are as follow:

1. The tetsubin without Kamayaki noticeably increases body and after taste. The performance of this model in terms of the water taste was the best among 3 tetsubins.
2. The tetsubin baked twice as long as ordinary tetsubin does not make the taste of water smooth at all. The intensity of the after taste was more or less the same as stainless steel kettle. However, the body was weaker than that of stainless steel electric kettle.
3. Kamayaki reduced the body of water regardless of the processing time

Non-Kamayaki produces the best result in terms of the taste

Based on the above experiment, I am affirm that the Kamayaki process affects the performance of a tetsubin. Ironically, the non-Kamayaki tetsubin produces strongest body and after taste, however, there is a downside as it is so easy to get rusty, so fast that it started rusting while I was using it. Since it gets rusty no matter how we use it, it is somehow not practical.

The Kamayaki may affect the surface structure of tetsubin

We found that the longer the Kamayaki is carried out, the lower the performance of tetsubin will be. I assume that it has something to do with the surface structure of tetsubin. Moreover, the inverse proportion between firing temperature and the performance was also observed using clay teapot. The higher firing temperature melts down the mineral granule and decreases the surface area. A tetsubin has more a complex and larger surface area as compared to the normal iron. Using the same theory, I would assume the reason for the decrease in performance after undergoing longer firing or higher baking temperature would be due to the melt-down of the particles and also, resulting in a decrease in surface area of tetsubin.

The type of charcoal used for Kamayaki affects the taste

Based on my investigation, I noticed that different brands of tetsubin use different types of charcoal where some would use hard charcoal and some soft charcoal. The firing temperature of hard charcoal is higher. If we just judge based on the taste, it would be more ideal to use soft charcoal.

Satetsu Tetsubin

Have you heard of “satetsu tetsubin”? Satetsu means sand-iron in English. Although the material used for satetsu tetsubin is not the same among the different manufacturers, the essential point is a satetsu tetsubin does not undergo the Kamayaki process. Originally, satetsu iron has higher density where it is said that the rust is unable to penetrate into the iron structure. Therefore, the satetsu tetsubin does not undergo the Kamayaki process. It produces a strong body and after taste. Long ago, I used to think that the satetsu tetsubin performed great due to its material. But for now, I believe that the main reason for a satetsu tetsubin to perform well is because there was no Kamayaki process performed. However, the satetsu material is very brittle. It may crack with a small mistake in handling which normal cast iron kettle would not.