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The owner of Mukasa-En, MUKASA Yasuyuki, is one of the most prominent tea farmers in Japan. His technique of tea cultivation and production is so sophisticated that tea farmers visit him to study his skills from many areas of Japan. … Continue reading
If a laser light is passed through some suspension which contains submicron or micron order particles, we can see the line of light scattering. For example, a water containing small amount of milk exhibits a red line of light scattering as follows.
The scattered light indicates the information about size, shape and motion of particles suspended in the liquid. Thus, light scattering can be used to measure the size, size distribution and motion of submicron-sized particles [Mat099]. The technique are applied to not only chemical industry but also biological use [156], environmental measurement and food industry etc.
As mentioned and shown previously (Part 1), tea infusion can scatter the laser light, exhibiting the red line of light scattering. Compared with the other liquid having similar color, we can obviously find the difference in the property of light scattering as follows.
A liquid left side is an energy drink containing mainly amino acids and vitamins. Its yellow color is derived from vitamin B. Although the color of both liquid are so clear we can see through the wood grain of table, however, only tea infusion does scatter the laser light while energy drink doesn’t scatter.
It is supposed that the difference is caused by the existence of polyelectrolytes sized between micron and submicron order.
We can observe the red line of light scattering in the case of each tea such as black tea, oolong tea, pan-fired tea, and bottled green tea.
Even in the case of a bottled tea, which has been filtrated by porous media to remove or prevent sediments and sedimentation in its manufacturing process.
Based on the of Ito En Ltd.[P001], the components such as polysaccharides and proteins which cause sediments are removed by porous material filtration and silica adsorption. Beside, the patent article describe that D90 is more than 3500 micrometers, indicating that polyelectrolytes still remain in the bottled tea after filtration and adsorption process.
We can observe the aggregation process in a cup of tea, especially in the case of deep-steamed green tea as follows.
Aggregates grow bigger with elapse time, resulting in settling on the bottom of teacup.
This change affected the taste and mouthfeel of tea, I felt.
When I tasted the tea after infusion immediately, I could feel somehow viscous. After sedimentation, the supernatant was seemed be mild and have delicate sweetness, as same as before settling, while it seemed to have lower viscosity compared with before sedimentation. The sediments-rich part seemed to be more viscous and its taste itself seemed to be same as before sedimentation. On the other hand, I felt stronger aftertaste, which changed from slight astringency and green flavor to sweet taste.
This sense is the reason why I suppose polyelectrolytes and their aggregates are essential for the body, aftertaste, mouthfeel of teas.
In the next part, I’d like to show some images about my speculation.
<References>
[Mat099] Williams K. An education material for the biophysics in Yale University.(URL : http://keck.med.yale.edu/biophysics/talks/6Folta-Stogniew_tcm284-30259_tcm284-284-32.pdf)
[156] Peetermans,J.A. et al. (1987) : European Biophysics Journal 15:65-69.
[P001] Ito En Ltd. Bottled green tea drink and its manufacturing process. WO2012029131 A1 (2012.03,08)
Tea has various polyelectrolyte, such as 4 types of catechins in green tea, pectins, polysaccharides, theaflavins and thearubigins in black tea, and so on.
We know these constituents determine tea taste.
In addition, complexes or aggregates of these polyelectrolyte could affect taste and mouthfeel of tea, in my personal opinion.
If laser light is applied to some solution which contain submicron size particles such as polyelectrolyte, the light scatters as depicted in some scientific blogs. We can see a red line of light scattering in the suspension. We obviously find the suspension turbid.
Tea infusion can also scatters laser light as follows, even though its color is clear as we can see through the wood grain of the table.
This means tea infusion contains submicron-size particles, although this tea infusion doesn’t seem to be turbid.
What are these particles?
I guess these could be the complexes or aggregates of tea polyelectrolyte.
Polyelectrolyte can aggregate by some mineral ions such as calcium, ferric ion, etc. and bind such ions making complexes. I think lower infusion rate of tea polyelectrolyte under higher concentration of calcium ion, as clarified by Sipro et al.[140]
I’d like to continue to post such kind of personal speculation.
[140] Spiro M., Price W.E., Miller W.M., Arami M. (1987) : Kinetics and equilibria of tea infusion: Part 8—the effects of salts and of pH on the rate of extraction of theaflavins from black tea leaf, Food Chemistry 25:117-126
Green tea “Sencha” has a potential to be brewed more than three times.
In Japan, it is recommended to infuse green tea at low temperature at first infusion and then re-steep at higher temperature than the previous infusion. An example of water temperature to infuse deep-steamed green tea “fukamushi cha” is shown as follows.
In this condition, extraction behavior of each constituents determining tea taste is shown in the following picture, based on results measured by Sakamoto et al. [089].
The first infusion makes us enjoy umami due to amino acids and delicate taste with fresh aroma. In the case of higher grade one, these flavors keep longer and finish smoothly and more gracefully.
The second infusion has a nice balance of umami with bitterness and astringency. In the case of higher grade one, in some minutes after sipping it, aftertaste can keep longer and change to sweet gradually. In the supposition of the author, this grdual change in aftertaste to sweet would be caused by the conformation change of taste-determining polyelectrolyte such as catechins, tannin, saccharides and their complexes, due to the change in their surrounding chemical conditions such as electrochemical potential and oxidation-reduction potential.
The third infusion has more bitter and astringent taste derived from catechins.
In addition to these taste, we can enjoy the change in infusion color also, especially in case of deep-steamed green tea. Till the third infusion, its color is getting deeper green with the progress of re-steeping.
As just described, we can find expressive faces of green tea by re-steeping.
Furthermore, we can arrange the flavor of green tea by adjusting water temperature and steeping time based on the extraction kinetics of each taste-determining constitution.
In my personal opinion, I prefer longer infusion time at 1st infusion, resulting in more umami and fine aftertaste for me.
Please try various arrangement of infusion conditions as you like!
<Reference>
[089] Sakamoto A., Nakagawa M., Sugiyama H., Horie H. (2002) The compositions of the respective infusions of Sencha brewed three times, Tea Research Journal94:45-55 (in Japanese)