gyokuro
ingredient / ingredient-gyokuro
玉露
Gyokuro is a type of high-grade sencha made from new shoots grown under shade. Shading is described as maintaining free amino acids and theanine, the umami components, at high concentrations. It uses the same shading-cultivation technique as tencha, but differs from tencha in being finished by rolling.
On this page (7 sections)
Reading the bitterness
Gyokuro does not necessarily have all of its tastes weaken equally when the same tea leaves are steeped repeatedly. In a study that poured 50 mL of 60℃ hot water over 3 g of commercial Uji gyokuro and examined up to 3 infusions under conditions of 0.5 to 4 minutes, 15 faculty and staff members rated bitterness, astringency, and other attributes on a scale of −2 to +2. Bitterness and astringency stayed at a moderate level across the 1st to 3rd infusions, with only small changes across infusion number.
Meanwhile, in the same evaluation, the 1st infusion had somewhat stronger sweetness, umami, and overall taste, and was somewhat more liked. As infusions were repeated, the scores for overall taste and preference fell. Even when the scores for bitterness and astringency did not move much, how gyokuro's overall taste is perceived can still change. However, this is a result examined in 1 commercial sample at 60℃, and the same change does not necessarily occur with other gyokuro or water temperatures.
There is also a study that separated out the umami side. 3 commercial gyokuro products, 10 g each, were steeped in 60 mL of 50℃ water for 2.5 minutes, their components were analyzed, and a model solution was made based on those values. In triangle tests removing each component, a decrease was identified in umami with glutamic acid, in sweetness with theanine, and in body and in the sweetness remaining after drinking with citric acid. This solution lacked the bitter-and-astringent components and aroma, and this is not a result that reproduced gyokuro itself or its bitterness.
Another trial that examined light-exposure time after removing the shading cover confirmed that, under the view that a tea high in the umami component amino acids and low in the astringency component catechins ranks as high quality, the longer the exposure time, the more amino acids decreased and catechins increased. The sensory score also tended to be lower the longer the exposure time.
Sources for this overview
各種製茶の煎出条件とカフェイン・タンニン溶出量及び味との関係
Checked for this overview: Supports the gyokuro sample amount, water temperature and volume, steeping time, the 3 infusions, the 15-person scale, and the result that bitterness and astringency changed little. / Supports the sweetness, umami, overall taste, and preference in the 1st infusion, the change across repeated infusions, and the caveat of a single commercial product and a fixed water temperature.
Checked for this overview: Supports the steeping and analysis conditions for the 3 gyokuro products, the taste changes from removing model-solution components, and the caveat of no bitter-astringent components or aroma.
Checked for this overview: Used for the trend of amino acids and catechins with exposure time, the positioning of catechins as the astringency component, and the trend in sensory scores
Structured claims — open a section to read each claim's confidence, evidence and limits
Composition and content (1)
Scope: Fukuoka Prefectural Agriculture and Forestry Research Center, Yame Branch; gyokuro 'Yabukita'; 2006 field trial (3 replicates)
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ingredient-gyokuro —has_composition→ (the claim sentence above)Sensory (3)
Scope: 1 sample of commercial Uji gyokuro. 15 faculty and staff members of a women's junior college individually rated bitterness, astringency, and other attributes on a 5-point scale of −2 to +2
Note: A result summarizing the average for each steeping time and the score for the representative 3-minute infusion. Changes in caffeine and tannin concentration are not equated with the sensory scores.
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ingredient-gyokuro —has_sensory_response→ (the claim sentence above)Scope: 1 sample of commercial Uji gyokuro, with the same tea leaves used for up to 3 infusions. A 5-point evaluation of −2 to +2 by 15 faculty and staff members of a women's junior college
Note: This is a within-test comparison showing that while the change in bitterness and astringency was small, sweetness, umami, overall taste, and preference showed a different pattern of movement.
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ingredient-gyokuro —has_sensory_response→ (the claim sentence above)Scope: An aqueous solution of amino acids and organic acids modeled on gyokuro infusion. Triangle tests, with 10 or more people per item, conducted by institute staff, temporary staff, and trainees
Note: The model solution lacks bitter-and-astringent components such as catechins and aroma; this is not a test that measured the contribution to the taste or bitterness of actual gyokuro itself.
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ingredient-gyokuro —has_sensory_response→ (the claim sentence above)How processing and cooking change it (1)
Scope: Fukuoka Prefectural Agriculture and Forestry Research Center, Yame Branch; gyokuro cultivars 'Yabukita' and 'Okuyutaka'; a 2006 field trial (3 replicates)
Note: The subject is gyokuro, not tencha (the raw material for matcha) itself. However, gyokuro and tencha belong to the same family of shading-cultivation techniques and involve the same mechanism -- shading changing amino acid / catechin composition. Note that the sensory evaluation uses overall items such as "flavor" from the standard tasting method, not a scale that isolates bitterness alone.
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ingredient-gyokuro —has_composition→ (the claim sentence above)