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Hi all,

I'm interested in learning more about the effects tetsubin have on tea from a scientific perspective. I'm not interested in subjective experience based on brewing, but I'd like to know what using a tetsubin does, and why! I've tried to find some research on this and haven't found anything yet, so I'm curious.

tealifehk wrote: ↑

Sun Dec 31, 2017 7:37 pm

Hi all,

I'm interested in learning more about the effects tetsubin have on tea from a scientific perspective. I'm not interested in subjective experience based on brewing, but I'd like to know what using a tetsubin does, and why! I've tried to find some research on this and haven't found anything yet, so I'm curious.

When I put mine full of water on a heat source, especially a charcoal stove, it heats the water and then if I pour that water over my tea it makes it taste good. That’s my science for you.

CWarren wrote: ↑

Sun Dec 31, 2017 8:32 pm

tealifehk wrote: ↑

Sun Dec 31, 2017 7:37 pm

Hi all,

I'm interested in learning more about the effects tetsubin have on tea from a scientific perspective. I'm not interested in subjective experience based on brewing, but I'd like to know what using a tetsubin does, and why! I've tried to find some research on this and haven't found anything yet, so I'm curious.

When I put mine full of water on a heat source, especially a charcoal stove, it heats the water and then if I pour that water over my tea it makes it taste good. That’s my science for you.

Pretty subjective there but I have had good results when boiling water in mine (on gas) and brewing with it. I'm more interested in hearing about what's actually happening and why. There is a possibility using a tetsubin might actually make worse tea!

https://www.hindawi.com/journals/jfq/2017/1805047/

It appears adding iron (as ferrous sulphate) to tea causes it to bind with polyphenols, which then are excreted through the digestive tract.

Canadian water filtration company and their target ranges for water pH/hardness/solutes for tea infusion:

https://danamark.com/applications/tea/

So it appears iron does bind readily with polyphenols. What are polyphenols?

https://en.wikipedia.org/wiki/Phenolic_content_in_tea

"Polyphenols found in green tea include but are not limited to epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin."

These (EGCG in particular) are believed to have positive health benefits, but do they impact flavor?

https://ratetea.com/topic/tannins-in-tea/70/

Iron binds with tannins in tea, including catechins. This means water from tetsubin may reduce astringency and bitterness while slightly reducing body. Perhaps the longer charcoal boil in cwarren's case means a higher ppm of iron? Some of the good stuff in green tea would be lost, but the ppm of iron in the water from using a tetsubin is probably very low. IMO tetsubin therefore are likely to have a very subtle effect. I'd like to see numbers on this some time and also a double blind taste test. I came across something that said cooking in cast iron only contributed a tiny bit of ppm/L: I'd wager tetsubin also contribute a tiny bit of iron from use.

Hoping someone can test the ppm/L of iron contributed to tea-quality water from new and used tetsubin.

Some good information here:
http://hojotea.com/categ_e/tetsubin.htm
http://hojotea.com/en/posts-61/
http://hojotea.com/en/posts-27/

Thanks Elise, I was aware of Hojo's writing on tetsubin, but was looking for solid science vs conjecture. I found it interesting that he claims burning charcoal doesn't generate moisture and therefore doesn't cause rust: burning charcoal does indeed give off water vapor!

I would say “solid scientific” writings about tetsubin would only be found in Japanese, I’ll see if I can find something though.

tealifehk wrote: ↑

Tue Jan 02, 2018 5:28 pm

I found it interesting that he claims burning charcoal doesn't generate moisture and therefore doesn't cause rust: burning charcoal does indeed give off water vapor!

From my understanding, charcoal consists essentially of pure carbon, so there is no hydrogen that would produce the water molecule. Of course, there will be some impurities, and trapped moisture, but relatively low amount (?), low enough that the produced water vapour wouldn't condensate on the vessel. The statement is probably meant in contrast with alcohol or gas burning which produces quite a lot of water.

Elise wrote: ↑

Tue Jan 02, 2018 3:28 pm

Some good information here:
http://hojotea.com/categ_e/tetsubin.htm
http://hojotea.com/en/posts-61/
http://hojotea.com/en/posts-27/

There's some confusingly conflicting information on the kamayaki (activation of the iron):

The first article (undated) says that this is the essential procedure to make the tetsubin affect the water:
"Without this process, cast iron kettle is nothing but kettle. It does not really change the taste of water and tea."

While the second article (from 2013) claims the opposite:
"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... 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."

Are his experimental observations contradicting his marketing?

Anyways, this is an interesting source of information.

.m. wrote: ↑

Wed Jan 03, 2018 9:38 am

tealifehk wrote: ↑

Tue Jan 02, 2018 5:28 pm

I found it interesting that he claims burning charcoal doesn't generate moisture and therefore doesn't cause rust: burning charcoal does indeed give off water vapor!

From my understanding, charcoal consists essentially of pure carbon, so there is no hydrogen that would produce the water molecule. Of course, there will be some impurities, and trapped moisture, but relatively low amount (?), low enough that the produced water vapour wouldn't condensate on the vessel. The statement is probably meant in contrast with alcohol or gas burning which produces quite a lot of water.

It seems charcoal contains 1-10% moisture from absorption from the atmosphere. That's quite a bit!

.m. wrote: ↑

Wed Jan 03, 2018 9:54 am

Elise wrote: ↑

Tue Jan 02, 2018 3:28 pm

Some good information here:
http://hojotea.com/categ_e/tetsubin.htm
http://hojotea.com/en/posts-61/
http://hojotea.com/en/posts-27/

There's some confusingly conflicting information on the kamayaki (activation of the iron):

The first article (undated) says that this is the essential procedure to make the tetsubin affect the water:
"Without this process, cast iron kettle is nothing but kettle. It does not really change the taste of water and tea."

While the second article (from 2013) claims the opposite:
"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... 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."

Are his experimental observations contradicting his marketing?

Anyways, this is an interesting source of information.

I think he's saying a balance is needed with kamayaki; too much and you ruin the kettle. Too little and you don't reduce the Fe 3+ to Fe 2+. Unfortunately rust converts some of the Fe 2+ back to Fe 3+. In both cases, though, you are losing a little something when the iron ions hit compounds in the tea. How much is lost? I don't know, and would it even be detectable to the human palate? Also an unknown.