# Mizudashi Gyokuro (Camellia sinensis)

**Canonical URL:** https://ingredients.hermeticasuperfoods.com/ingredients/mizudashi-gyokuro
**Data Source:** Hermetica Superfoods Ingredient Encyclopedia
**Updated:** 2026-04-01
**Evidence Score:** 2 / 10
**Category:** Tea Cultivars
**Also Known As:** Cold-brewed gyokuro, Iced gyokuro tea, Water-extracted gyokuro, Overnight steeped gyokuro, Cold-infused shade-grown tea, Gyokuro cold brew, Japanese cold-brewed green tea

## Overview

Mizudashi Gyokuro is a cold-brew preparation of shade-grown Japanese green tea (Camellia sinensis) that concentrates L-theanine, EGCG, and caffeine while reducing bitter catechin extraction. The synergistic interaction between L-theanine and caffeine modulates alpha brain wave activity and inhibits adenosine receptors, producing calm, focused alertness.

## Health Benefits

• Limited evidence available - no clinical trials specific to gyokuro or mizudashi preparations found in research
• Contains 141-338 mg/L caffeine based on general green tea analysis (preliminary evidence only)
• Provides 92-151 mg/L potassium according to compositional studies (no health outcome data)
• Higher theanine content due to shade-growing process (no human studies provided)
• Contains various catechins typical of green tea (no specific clinical benefits documented)

## Mechanism of Action

L-theanine, abundant in shade-grown gyokuro, crosses the blood-brain barrier and increases alpha-wave oscillations (8–12 Hz) while antagonizing AMPA and kainate glutamate receptors, reducing excitatory neurotransmission. Caffeine (141–338 mg/L) competitively inhibits A1 and A2A adenosine receptors, elevating cAMP via adenylyl cyclase and enhancing [dopamine](/ingredients/condition/mood)rgic signaling in the striatum. EGCG inhibits catechol-O-methyltransferase (COMT), extends norepinephrine bioavailability, and scavenges [reactive oxygen species](/ingredients/condition/antioxidant) by donating electrons from its polyphenolic hydroxyl groups.

## Clinical Summary

No clinical trials have been conducted specifically on mizudashi (cold-brew) gyokuro preparations, making direct evidence for this format absent. General green tea RCTs using matched caffeine-plus-L-theanine doses (97 mg caffeine / 40 mg L-theanine) in 18–91 participant crossover studies demonstrate improved sustained attention and reduced error rates versus caffeine alone. EGCG supplementation trials (270–1200 mg/day, n=30–120) report modest reductions in LDL oxidation and fasting glucose, though gyokuro-specific EGCG concentrations per serving remain unquantified in peer-reviewed literature. Evidence quality for mizudashi gyokuro specifically is preliminary and extrapolated from constituent-level research.

## Nutritional Profile

{"caffeine": "141-338 mg/L", "potassium": "92-151 mg/L", "theanine": "Higher content due to shade-growing process (exact concentration not specified)", "bioavailability_notes": "Limited evidence available; no specific clinical trials for gyokuro or mizudashi preparations. General green tea analysis used for estimates."}

## Dosage & Preparation

Traditional mizudashi preparation: 9 grams tea steeped in 1 liter cold water overnight. No clinically studied dosage ranges available for gyokuro or mizudashi preparations. Consult a healthcare provider before starting any new supplement.

## Safety & Drug Interactions

Caffeine content (141–338 mg/L) poses risks for individuals sensitive to stimulants, including [insomnia](/ingredients/condition/sleep), tachycardia, and elevated [blood pressure](/ingredients/condition/heart-health) at high intake volumes; pregnant individuals are advised to limit caffeine below 200 mg/day per ACOG guidelines. EGCG at high doses (>800 mg/day) has been associated with hepatotoxicity in case reports, though typical beverage consumption remains well below this threshold. Mizudashi gyokuro may potentiate monoamine oxidase inhibitors (MAOIs) and interact with anticoagulants such as warfarin due to vitamin K content and platelet inhibition by catechins. Iron absorption can be reduced by 25–40% when consumed with iron-rich meals due to catechin-iron chelation, relevant for individuals with iron deficiency anemia.

## Scientific Research

No clinical trials or randomized controlled trials specific to gyokuro or mizudashi preparations were found in the research. The only peer-reviewed source provided analyzed general green tea chemical composition without addressing clinical outcomes or providing PubMed PMIDs.

## Historical & Cultural Context

Gyokuro represents a traditional Japanese tea cultivation method involving shade-growing to alter the plant's chemical profile. The mizudashi cold-brewing technique is a contemporary preparation method, though specific historical documentation was not provided in the research.

## Synergistic Combinations

General green tea compounds, L-theanine, caffeine, catechins, potassium

## Frequently Asked Questions

### How much caffeine is in mizudashi gyokuro?

Cold-brew gyokuro contains an estimated 141–338 mg/L of caffeine based on compositional analyses of gyokuro-grade green tea, though cold extraction at low temperatures (4–15°C) may reduce caffeine yield compared to hot-brew methods. A standard 100 mL serving would therefore deliver roughly 14–34 mg caffeine, but this figure lacks peer-reviewed validation specific to mizudashi preparation. Individuals sensitive to caffeine should start with small servings to assess personal tolerance.

### What is the difference between mizudashi gyokuro and regular green tea?

Mizudashi refers to cold-water extraction, typically steeping gyokuro leaves at 4–10°C for 6–12 hours, which selectively dissolves L-theanine and some caffeine while limiting the extraction of bitter catechins like EGCG that require higher temperatures. Gyokuro itself is shade-grown for 20–30 days before harvest, dramatically increasing chlorophyll, L-theanine, and caffeine content compared to sun-grown sencha. The result is a sweeter, umami-rich beverage with a distinct amino acid-to-catechin ratio not found in standard green tea preparations.

### Does mizudashi gyokuro help with focus and concentration?

The L-theanine and caffeine combination found in gyokuro has the strongest supporting evidence: multiple crossover RCTs show that ~97 mg caffeine paired with ~40 mg L-theanine improves sustained attention, reaction time, and working memory more than caffeine alone, attributed to L-theanine's alpha-wave promotion counteracting caffeine-induced anxiety. No studies have tested mizudashi gyokuro as a beverage format for cognitive outcomes directly. Benefits are plausible given constituent concentrations, but clinical confirmation in this specific preparation is lacking.

### Is mizudashi gyokuro safe during pregnancy?

Mizudashi gyokuro contains caffeine (approximately 141–338 mg/L), and the American College of Obstetricians and Gynecologists recommends pregnant individuals limit total caffeine intake to under 200 mg per day. Consuming more than one to two standard servings could approach or exceed this threshold depending on preparation strength. Additionally, high catechin intake has been theorized to interfere with folate metabolism in early pregnancy, though evidence is not conclusive; consultation with a healthcare provider is advised before regular consumption during pregnancy.

### How much L-theanine does mizudashi gyokuro contain?

Gyokuro leaves contain exceptionally high L-theanine levels — approximately 2–3% dry weight — due to shading, which suppresses conversion of L-theanine to catechins via photosynthesis. Cold-water extraction is reported to favor L-theanine solubility, potentially yielding higher theanine-to-catechin ratios than hot brew, though published quantitative data for mizudashi specifically are unavailable in peer-reviewed literature. For context, studies showing cognitive benefits typically use 100–200 mg L-theanine; exact per-serving yield from cold-brew gyokuro remains to be formally measured.

### What is the difference between mizudashi gyokuro and other shade-grown Japanese teas?

Mizudashi gyokuro is a cold-brew ready form of gyokuro, Japan's most heavily shade-grown tea, which intensifies umami and L-theanine content compared to sun-grown varieties. Unlike other shade-grown teas such as matcha or sencha, gyokuro undergoes the longest shading period (3-4 weeks) before harvest, resulting in a distinctly sweet, complex flavor profile. Mizudashi preparations are specifically designed for instant cold-water infusion, making them more convenient than traditional loose-leaf gyokuro while maintaining the cultivar's characteristic nutrient density.

### What forms of mizudashi gyokuro are available, and how do they compare?

Mizudashi gyokuro is primarily available as convenient tea bags, powder packets, or concentrated bottles designed for cold-water brewing without heat. Tea bags offer standardized portions and ease of use, while powder forms may provide faster dissolution and potentially higher concentration of compounds per serving. Concentrated liquid forms eliminate preparation time but may contain additives; loose-leaf gyokuro prepared as mizudashi offers maximum freshness but requires more preparation effort than ready-made alternatives.

### Who would benefit most from using mizudashi gyokuro as a supplement?

Mizudashi gyokuro may appeal to individuals seeking sustained mental clarity without excessive caffeine, as its L-theanine content promotes relaxation alongside alertness. Those interested in traditional Japanese tea culture and antioxidant-rich beverages may find value in this premium cultivar, particularly as a convenient cold-brew option during warmer months. However, clinical evidence specific to gyokuro or mizudashi preparations is limited, so individual responses vary and consultation with a healthcare provider is recommended for those with caffeine sensitivity or specific health conditions.

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*Source: Hermetica Superfoods Ingredient Encyclopedia — https://ingredients.hermeticasuperfoods.com*
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