Sometimes, looking for answers requires asking the right questions. So I went with the theme of iron concentration, that there might be an optimal concentration for detecting iron as 'sweet' versus 'bitter or astringent'.
Well, yeah, that turns out to be the case, but it's a tad more complex.
For starters, it depends strongly on the minerals present and their charge state.. It also depends on the metal counterion present. Sulfur is one of the most commonly found counterions in drinking water.
Detection and assigned flavor of dissolved minerals in water is a subjective quality of the oral cavity (nose is an active player here), personal experience, physical health, etc.
My educated guess is there is a bit of ion exchange going on with these iron rich activated clays and iron complexes in unlined tetsubin.
There is no 'seasoning' (as in the deposition of insoluble tea complexes that changes the surface of clays/clay pores, as in yixing teapots used with oxidized teas) per se.
A bit of science for those interested in the details.
Sensitivity of Assessors to Ferrous Salts. Czech J. Food Sci.
Vol. 27, 2009, Special Issue
http://journals.uzpi.cz/uniqueFiles/07935.pdf
Qualitative Differences of Divalent Salts: Multidimensional Scaling and Cluster Analysis. Chemical Senses 2005 30(9):719-726.
http://chemse.oxfordjournals.org/cgi/co ... l/30/9/719
Detection thresholds and taste qualities of iron salts. Food Quality and Preference
2006. 17(6):513-521 (Vol 17, issue six, pages 513-521).
http://www.sciencedirect.com/science/journal/09503293
Retronasal smell and detection thresholds of iron and copper salts. Physiology & Behavior. 2007. 92(3):487-491.
http://www.sciencedirect.com/science/journal/00319384
On a practical note, in drinking water treatment, standard practice here in the US is to reduce the iron concentration to a low level (50 micrograms/L), when the dissolved mineral (calcium and magnesium) concentration is low and dissolved sulfur salts are present, to remove metallic/bitter taste arising from iron sulfate.
So, there may be a light at the end of the tunnel, with respect to the assertion of sweetness arising from use of iron-rich surfaces that 'treat' water used for making green tea.
However, your perception of benefit gained may depend on:
(1) water quality and dissolved minerals present
(2) your mood and physical health status that affect taste/odor receptor sensitivity
(3) oral health (including biofilm properties) and history of previous exposure to certain metal salts,
(4) the position of the moon and the stars
j/k with respect to number 4 :-)
(4)
By analogy.
Coconut shell activated carbon treatment is said to provide 'sweet-tasting' water for preparing green tea.
Physical and chemical treatment processes associated with porous activated carbon surfaces used in water purification includes physical sorption of insoluble (hydrophobic) organic contaminants, binding and retention of ions (acids, bases and salts), and catalytic conversion (change in valency/oxidation state and binding of multivalent metal cations (zinc, iron, lead, copper, arsenic, selenium, etc).
Clay used for making pottery is a complex mixture that may comprise as little as 1/3 mined and processed clay by mass. The surface may therefore be assumed to be a chemically complex environment, perhaps (treading cautiously here) by analogy, behaving physically and chemically like that of activated carbon.
*snaps fingers*
You know, I bet our resident teaware artisans might be able to provide us a bit of insight on the clay chemistry at work in these Japanese unglazed clay teapots.
Physical and chemical treatment processes associated with porous activated carbon surfaces used in water purification includes physical sorption of insoluble (hydrophobic) organic contaminants, binding and retention of ions (acids, bases and salts), and catalytic conversion (change in valency/oxidation state and binding of multivalent metal cations (zinc, iron, lead, copper, arsenic, selenium, etc).
Clay used for making pottery is a complex mixture that may comprise as little as 1/3 mined and processed clay by mass. The surface may therefore be assumed to be a chemically complex environment, perhaps (treading cautiously here) by analogy, behaving physically and chemically like that of activated carbon.
*snaps fingers*
You know, I bet our resident teaware artisans might be able to provide us a bit of insight on the clay chemistry at work in these Japanese unglazed clay teapots.
Jul 16th, '09, 15:47
Posts: 147
Joined: Apr 17th, '09, 11:36
Location: Mississippi
I have been spoiled in the southwestern US, they have great natural water supplies. Tons of natural filtration through fine grained sandstones. Probably the best water I have ever had came from an artesian well in Moab, Utah (FO FREE!). It was through sandstone- almost "pure" Si02 baby! The water was quite "soft", but not too flat.
Here in MS though, our soils are FULL of hematite yucky because of this in my opinion. Which makes me agree with Intuit on Fe concentration playing a significant role in taste/quality. The water here is not as good as the water out west with low iron content.
My Pur filter has cracks in it, shoots around like a squirt gun hehe, love using it on unsuspecting guests
Chlorine and very fine grained sediment are my greatest foes in my tap water! Get rid of that and its all good.
Sorry if none of this makes any sense...just my 10 cents. I don't understand how you guys get so picky, no offense, I used public restroom water in a dorm called "Kin-compton" for everything for almost a year. Drank water out of nasty looking ponds with my water bottle that has a filter in it. Maybe my palate is a weakling, not too sensitive. I say go to Moab's artesian well, and filler up! hahaha
Here in MS though, our soils are FULL of hematite yucky because of this in my opinion. Which makes me agree with Intuit on Fe concentration playing a significant role in taste/quality. The water here is not as good as the water out west with low iron content.
My Pur filter has cracks in it, shoots around like a squirt gun hehe, love using it on unsuspecting guests
Chlorine and very fine grained sediment are my greatest foes in my tap water! Get rid of that and its all good. Sorry if none of this makes any sense...just my 10 cents. I don't understand how you guys get so picky, no offense, I used public restroom water in a dorm called "Kin-compton" for everything for almost a year. Drank water out of nasty looking ponds with my water bottle that has a filter in it. Maybe my palate is a weakling, not too sensitive. I say go to Moab's artesian well, and filler up! hahaha
Jul 16th, '09, 15:50
Posts: 147
Joined: Apr 17th, '09, 11:36
Location: Mississippi
Re: By analogy.
I'd love to know what the clay chemistry is also. Hearing purple clay, brown clay, pink clay, yellow clay, green clay isn't very descriptive or helpful. My guess is its some form of kaolinite?Intuit wrote: You know, I bet our resident teaware artisans might be able to provide us a bit of insight on the clay chemistry at work in these Japanese unglazed clay teapots.
Probably
"Potter's clay is found in very large quantities in the provinces of Yamashiro, Hoki, Turoo Iyo, Hizen, Higo, Owari, Mikaera, Idyn, Musashi, and Mino."
The Pottery And Porcelain Industries Of Japan.
http://chestofbooks.com/crafts/scientif ... Japan.html
Tokoname is known for it's kilns, one of six ancient pottery producing cities; for instance, the Seto kilns have been in continuous operation for 2000 years and are thought to have been in periodic operation for as long as 10,000 years. Various clays were mined and transported to these kiln centers; in the modern era, clay type and mixture composition varied according to the type of wares (earthenware, hard pottery, porcelain/vitreous china and stoneware) according to the product type desired.
Typical Banko and Tokoname redware was produced from materials mined from a long thin sedimentary deposit nearby.
" Tokoname has been a pottery town since the 12th century. There are a hundred kilns in town, and most are wood-fired. Most of the clay is local and simply dug from the ground. They have a gorgeous black/gray clay and they're known for the red clay that is used for teapots."
Mentions that lengthy Tokoname wood firing sessions may last for days at at time, with the kilns being manned in shifts.
http://www.watsonwalker.com/travel/japan2002/index.html (Japan travelogue of a pottery-savvy couple)
Tokoname and Banko 'red' clays are known to be mixed-type high iron clays.
Yixing clays are also mixed-type (kaolinite/smectite) high-iron, predominantly kaolinite.
http://en.wikipedia.org/wiki/Yixing_clay
Clay pottery production has been dated to ~ 12,700 BP in Japan.
Jomon Pottery Production in Central Japan. Journal of Archaeology for Asia and the Pacific, Vol. 38 1999.
The Pottery And Porcelain Industries Of Japan.
http://chestofbooks.com/crafts/scientif ... Japan.html
Tokoname is known for it's kilns, one of six ancient pottery producing cities; for instance, the Seto kilns have been in continuous operation for 2000 years and are thought to have been in periodic operation for as long as 10,000 years. Various clays were mined and transported to these kiln centers; in the modern era, clay type and mixture composition varied according to the type of wares (earthenware, hard pottery, porcelain/vitreous china and stoneware) according to the product type desired.
Typical Banko and Tokoname redware was produced from materials mined from a long thin sedimentary deposit nearby.
" Tokoname has been a pottery town since the 12th century. There are a hundred kilns in town, and most are wood-fired. Most of the clay is local and simply dug from the ground. They have a gorgeous black/gray clay and they're known for the red clay that is used for teapots."
Mentions that lengthy Tokoname wood firing sessions may last for days at at time, with the kilns being manned in shifts.
http://www.watsonwalker.com/travel/japan2002/index.html (Japan travelogue of a pottery-savvy couple)
Tokoname and Banko 'red' clays are known to be mixed-type high iron clays.
Yixing clays are also mixed-type (kaolinite/smectite) high-iron, predominantly kaolinite.
http://en.wikipedia.org/wiki/Yixing_clay
Clay pottery production has been dated to ~ 12,700 BP in Japan.
Jomon Pottery Production in Central Japan. Journal of Archaeology for Asia and the Pacific, Vol. 38 1999.
Jul 16th, '09, 18:44
Posts: 147
Joined: Apr 17th, '09, 11:36
Location: Mississippi
Smectites normally absorb right? They are "swelling" clays, so maybe that is why they can influence taste so much in yixing and tokoname, blah blah blah clays. Although I know that kaolinite isn't very keen to react under the earths surface conditions...its in pretty stable chemical equilibrium, but of course things could change depending on conditions, if lets say I decided to use a blow torch on my pots hee hee. jk
From my petrology book quite interesting to me--> isbn-978071673743
A single unit of kaolinite consists of one Si-O tetrahedral sheet and on Al-OH octahedral sheet, with essentially no cation substitution in either sheet. All other clays (and MICAS) are composed of three sheets, an octahedral sheet sandwiched between two tetrahedral sheets...fig in the book don't worry bout it....There is ABUNDANT substitution within all three sheets: Al for Si in the tetrahedral sheets, Mg and Ferrous iron for Al in the octahedral sheet. These substitutions cause charge imbalances within the sheets (Al^3+ vs. Si^4+; Mg^2+ and Fe^2+ versus Al^3+) that are rebalanced by the ABSORPTION of metallic cations on the surfaces of each clay flake. The cations adsorbed are those available in soil waters: the K^+ that was released from orthoclase, the Na^+ and Ca^2+ that were released from plagioclase and ferromagnesian minerals. Illite prefers potassium, SMECTITE prefers sodium and calcium.
BTW since these clays are young clays, they are more likely expandable clays.
I must mention Bowens reaction series as well-----> http://en.wikipedia.org/wiki/Bowen%27s_reaction_series
Also since these clays are fired at high temps me guesses? , also the chemistry will change from when it was dug out of the ground, duhs.
So my guess is that the clay can play an important role on taste, but at the same time I digress.....since these substitutions are not necessarily at the conditions in your kitchen while making tea hehehehehe
Trying to help Intuit , I am a noobie though haha, just trying to use my weak geology knowledge.
From my petrology book quite interesting to me--> isbn-978071673743
A single unit of kaolinite consists of one Si-O tetrahedral sheet and on Al-OH octahedral sheet, with essentially no cation substitution in either sheet. All other clays (and MICAS) are composed of three sheets, an octahedral sheet sandwiched between two tetrahedral sheets...fig in the book don't worry bout it....There is ABUNDANT substitution within all three sheets: Al for Si in the tetrahedral sheets, Mg and Ferrous iron for Al in the octahedral sheet. These substitutions cause charge imbalances within the sheets (Al^3+ vs. Si^4+; Mg^2+ and Fe^2+ versus Al^3+) that are rebalanced by the ABSORPTION of metallic cations on the surfaces of each clay flake. The cations adsorbed are those available in soil waters: the K^+ that was released from orthoclase, the Na^+ and Ca^2+ that were released from plagioclase and ferromagnesian minerals. Illite prefers potassium, SMECTITE prefers sodium and calcium.
BTW since these clays are young clays, they are more likely expandable clays.
I must mention Bowens reaction series as well-----> http://en.wikipedia.org/wiki/Bowen%27s_reaction_series
Also since these clays are fired at high temps me guesses? , also the chemistry will change from when it was dug out of the ground, duhs.
So my guess is that the clay can play an important role on taste, but at the same time I digress.....since these substitutions are not necessarily at the conditions in your kitchen while making tea
hehehehehe Trying to help Intuit
, I am a noobie though haha, just trying to use my weak geology knowledge.
im sleepy and not absorbing info well so I think we have discovered that my teapot is not seasoned. In comparing my glazed and unglazed, the banko holds onto the smell of the tea while the glazed does not. I haven't brewed in my banko for a few days and it still smells delicious. Wont that contribute future tea brewings?
Re: By analogy.
I have been using bamboo charcoal inside my Brita filtered water storage container. The difference is noticeable both in drinking tea and water. This alone, however, is still not enough to equal the flavor and aroma of certain teas made in certain teapots.Intuit wrote:Coconut shell activated carbon treatment is said to provide 'sweet-tasting' water for preparing green tea.
Physical and chemical treatment processes associated with porous activated carbon surfaces used in water purification includes physical sorption of insoluble (hydrophobic) organic contaminants, binding and retention of ions (acids, bases and salts), and catalytic conversion (change in valency/oxidation state and binding of multivalent metal cations (zinc, iron, lead, copper, arsenic, selenium, etc).
Clay used for making pottery is a complex mixture that may comprise as little as 1/3 mined and processed clay by mass. The surface may therefore be assumed to be a chemically complex environment, perhaps (treading cautiously here) by analogy, behaving physically and chemically like that of activated carbon.
*snaps fingers*
You know, I bet our resident teaware artisans might be able to provide us a bit of insight on the clay chemistry at work in these Japanese unglazed clay teapots.
Also, to address the clay issues of Tokoname and Banko, specifically, I asked Hojo about Tokoname clay and its purity. He told me it was all mixed clay with artificial color added (oxides). I asked about older pots and he told me we would have to go back maybe 100 years to get the pure clay. And, with regards to Banko, not all are reduced, although he claims the clay is pure, no additives.
I have a Masaki kyusu and an older dark red Hobin. Brewing green tea in each makes a different taste. The Masaki always smoothes out the astringency taking away the bite that green tea can have. But, it is not good for green oolongs because the flavor is muted too much for my taste.
I have never drank from a Tokoname teapot and have not seen any comaparisons here between it and a banko. So many lovely Tokoname designs and artists working to create the beautiful pots. Can anyone give a good comparison between a Tokoname and reduction fired Bangko pot?
>Banko, not all are reduced, although he claims the clay is pure, no additives.
Yes, it's quite apparent from the color variety in Banko teaware, although the majority I have seen aren't red, they've got that classic purple sheen.
A Banko clay trainee who posts to a Japanese blog, from a family has been making teaware for generations, reported that his attempts to use pure, unmixed clay were fruitless. The fired results were inferior. He's gone back to his father's recipe of mixed clays (plus sand/organic fillers).
Japanese pottery clay character is partially dependent on origin location. It will vary considerably in mineral and organic constituency in the raw state within deposits, too. Clay preparation is an art and this affects chemistry, does pottery forming and firing. These clay processing techniques are kept secret because of the intense competition between hundreds of pottery firms within each kiln center.
I have no doubt that the resulting teapots will vary considerably in their physical/chemical effect in tempering tea infusion characteristics when tested for with the same tea.
Your milage will also vary with sensory ability, all other factors held the same: water supply/season, tea source/harvest/age, teapot used, etc.
Yes, it's quite apparent from the color variety in Banko teaware, although the majority I have seen aren't red, they've got that classic purple sheen.
A Banko clay trainee who posts to a Japanese blog, from a family has been making teaware for generations, reported that his attempts to use pure, unmixed clay were fruitless. The fired results were inferior. He's gone back to his father's recipe of mixed clays (plus sand/organic fillers).
Japanese pottery clay character is partially dependent on origin location. It will vary considerably in mineral and organic constituency in the raw state within deposits, too. Clay preparation is an art and this affects chemistry, does pottery forming and firing. These clay processing techniques are kept secret because of the intense competition between hundreds of pottery firms within each kiln center.
I have no doubt that the resulting teapots will vary considerably in their physical/chemical effect in tempering tea infusion characteristics when tested for with the same tea.
Your milage will also vary with sensory ability, all other factors held the same: water supply/season, tea source/harvest/age, teapot used, etc.