1.3 What brewing actually does

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Tip

Module 1 · Lesson 3 of 4 — part of 1. The Chemical Core. New here? Start at the module hub for the full chapter map.

Superscript numbers are clickable footnotes (jump to the source, caret jumps back; hover often pops the note). Collapsed “More detail…” boxes hold solubility tables, ISO strength numbers, and second-steep physics so the open page stays kitchen language.

The only lab most of us own

You already met the plant (Lesson 1.1) and the factory fork (Lesson 1.2). Now the leaf is in your hands. Brewing is not magic and it is not “just waiting.” It is hot (or cold) water acting like a selective extractor: some guests leave the leaf early and easily; one needs more heat and time—the way a tea bag clouds a mug.

Classic infusion studies treated steeping as a measurable problem: how fast caffeine and related compounds leave the leaf, and how water temperature changes those rates.12

You only need three kitchen dials for the open story: time, temperature, and how much leaf. Dense milligram tables and lab-strength recipes live in the foldouts.

TipEveryday words for this sitting
  • Extraction — moving compounds from leaf into water.
  • Early guests — caffeine and L-theanine leave relatively easily.
  • Slower guest — EGCG wants more heat and time.
  • Cold brew — slow extraction in cold water; not caffeine-free.

Three guests, three exit speeds

Caffeine dissolves readily and comes out relatively easily. L-theanine is very happy in water even when cooler and also comes out early. EGCG—the standout green-tea plant compound—needs more heat and time. It is also less happy if the brew turns too alkaline.34

If you dunk a tea bag for ten seconds, the drink is pale and mild. If you leave it for minutes in hot water, it gets stronger. That is extraction: more time and heat usually mean more compounds in the water—until taste turns too bitter for you.

Think of three friends leaving a party. Two are already at the door. One is still finishing a conversation in the kitchen. Heat and time persuade that third friend to leave—but shout too long and the party gets harsh.

Compound How it behaves in water Notes from sources
Caffeine Dissolves readily; much more soluble as water heats About 20 g/L at 20°C; much higher near boiling5
L-Theanine Very soluble even at lower temperatures About 350 g/L at 25°C; cup yields depend on tea type and brew time6
EGCG Needs more heat; less stable if the brew is too alkaline Water extraction of green-tea catechins is often most efficient near about 80°C for a timed steep; very hot, long steeps risk degradation7

Keenan and colleagues measured how much L-theanine actually lands in a real cup. For a 200 mL cup steeped two minutes, they reported roughly 24 mg in ordinary black tea, lower averages for some specialty blacks and whites, and roughly 8 mg in the green teas they tested—with brew time as the big dial.8 Shaded Japanese greens (Gyokuro, Matcha) can sit higher still; the Cup reference keeps those everyday ranges in one place.

Perva-Uzunalić and colleagues mapped how temperature and time change catechin and caffeine recovery from green tea. Short, hot extractions can be efficient; pushing temperature and time too far starts to destroy the very catechins you hoped to pull.9

Classic infusion studies treated steeping as solid–liquid extraction: how fast caffeine and theaflavins leave the leaf, and how water temperature changes those rates.1011 Pack tables summarize effective diffusion at about 80°C as higher for caffeine and L-theanine than for EGCG—which matches the kitchen feel that EGCG is the “slow guest.”1213

Caffeine dissolves readily—on the order of 20 g/L at 20°C, about 108 g/L at 60°C, and hundreds of g/L near boiling in the pack/Spiro framing.14 L-theanine is extremely water-soluble even when cool (about 350 g/L at 25°C in solubility notes the packs cite), which is why it appears early in a steep.15 EGCG needs more heat and time (pack solubility near 33.8 g/L at 80°C), and it is less stable if the brew turns too alkaline (packs flag instability above about pH 6.5).16

Cold brew. Cold water slows extraction; it does not delete caffeine. Given enough time (often 12–24 hours in the literature discussed in the packs), caffeine can reach levels similar to—or above—a short hot steep.17

Temperature and what you feel later. Brewing green tea well below 80°C tends to lower the EGCG-to-caffeine ratio, so the cup you later feel is chemically skewed—not only milder in taste.18

Myth check: “Cold brew means no caffeine”

Cold water only slows extraction. Given enough time (often 12–24 hours in the literature discussed in the packs), caffeine in cold brew can reach levels similar to—or even above—a short hot steep.19 Smile politely at the “caffeine-free cold brew” story; then check the clock.

Particle size matters. A fine fanning grade in a tea bag has more surface area, so compounds often exit faster than from whole loose leaves—one reason a three-minute bag can taste “done” while a whole-leaf pot still has another steep in it. That is still the same extraction physics Spiro-style studies measured; only the geometry changed.2021

Lab vs kitchen strength. ISO 3103 (sensory preparation) uses about 2 g leaf per 100 mL boiling water—roughly 5 g per 250 mL—stronger than many home cups that use about 2 g per 250 mL.22 The Cup reference sticks to everyday baselines so lab and kitchen do not get confused.

What you control tomorrow morning

Dial Turn it up What usually rises first
Time Longer steep Caffeine + theanine early; bitterness/catechins later
Temperature Hotter water EGCG and overall strength; also risk of harshness
Leaf amount More grams per mug Everything—use the Cup reference, not vibes
Leaf style Broken bag grade vs whole leaf Speed of extraction (surface area)

A quiet bridge to Chapter 2

If you want more of the “green tea catechin” side of the cup, hotter water and a bit more time help EGCG extract—but they can also pull more bitter material. Caffeine and L-theanine are already relatively easy to extract.

There is also a quiet bridge from this kitchen scene to Chapter 2: EGCG needs more heat to extract well. Brewing green tea well below a comfortable green-tea temperature tends to skew the cup toward caffeine relative to EGCG. So temperature is not only about taste—it changes which compounds dominate the cup you later feel.23

Story in one minute

Brewing dissolves leaf solids into water. Caffeine and L-theanine exit easily. EGCG wants more heat and time—and can degrade if you overcook the cup. Cold brew only slows the clock; it does not delete caffeine. Your mug strength is usually weaker than tasting-lab liquor, which is why lab headlines and kitchen feelings disagree.

TipYou can stop here
  • Hot water is a selective extractor: some guests leave early; EGCG needs more heat and time.
  • Time, temperature, and leaf amount are the three dials you actually own.
  • Cold brew slows caffeine exit—it does not delete it.
  • Want calmer-focus chemistry? Do not fear a full timed steep—theanine comes out early—but match temperature to style (greens often near a comfortable hot, not a rolling boil).
  • Want maximum catechin extraction from green tea? Heat and time help until bitterness and degradation win.24
  • Believe cold brew is caffeine-free? Re-read the kinetics.25

A practical, fact-based starting pattern many drinkers use after this lesson:

  1. Weigh or habit-ballpark leaf (home cups often ~2 g / 250 mL—not ISO’s stronger liquor).26
  2. Greens: water near 80°C, timed steep; taste before you punish the cup.
  3. Blacks: near-boiling is common; bitterness is your brake pedal.
  4. Want cold brew? Budget hours, not seconds, and assume caffeine will show up.27
  5. Compare your results with the Cup reference ranges—not with capsule-trial milligrams from Module 2.

This is kitchen literacy, not a prescription.

  1. Extraction = heat × time × surface area × leaf amount.
  2. Caffeine & theanine = early guests; EGCG = slower, heat-hungry guest.
  3. Cold ≠ caffeine-free.
  4. ISO liquor ≠ home mug.28
  5. Temperature changes which compounds dominate—not only how strong the cup tastes.

A second cup: why the second steep tastes different

Whole-leaf drinkers already know the plot twist: the first steep is not the whole story. Because caffeine and L-theanine exit relatively early, a first infusion can feel brisk and stimulating, while later steeps—especially with greens and oolongs—shift toward softer amino-acid and aroma notes as the easy guests have partly left.2930 Broken bag grades compress that drama into one fast act: high surface area, quick dark liquor, fewer polite second chances.

That is still extraction physics, not mysticism. It is also why “I used the same grams” can produce different cups when leaf style changes.

Module 2 will talk about calm focus and stress markers after you swallow. This lesson’s quiet warning: if you brew green tea far below ~80°C, you may skew the cup toward caffeine relative to EGCG.31 You did not invent a new plant—you changed the guest list. Pair that with Chapter 1’s timing clocks (Lesson 1.4) and you get a fairer reading of “this tea felt different today.”

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Footnotes

  1. Spiro, M., & Jago, D. S. (1982). Kinetics and equilibria of tea infusion: Kinetics of extraction of caffeine and theaflavins. Journal of the Science of Food and Agriculture, 33(4), 333–340.↩︎

  2. Spiro, M., & Siddique, S. (1981). Kinetics and equilibria of tea infusion: Part 1. Analysis and partition constants of the components of black tea. Journal of the Science of Food and Agriculture, 32(10), 1027–1032.↩︎

  3. Keenan, E. K., et al. (2011). How much theanine in a cup of tea? Effects of tea type and method of preparation. Food Chemistry, 125(2), 588–594. https://doi.org/10.1016/j.foodchem.2010.08.071↩︎

  4. Perva-Uzunalić, A., et al. (2006). Extraction of active ingredients from green tea (Camellia sinensis): Extraction efficiency of major catechins and caffeine. Food Chemistry, 96(4), 597–605. https://doi.org/10.1016/j.foodchem.2005.03.015↩︎

  5. Spiro, M., & Jago, D. S. (1982). Kinetics and equilibria of tea infusion: Kinetics of extraction of caffeine and theaflavins. Journal of the Science of Food and Agriculture, 33(4), 333–340.↩︎

  6. Keenan, E. K., et al. (2011). How much theanine in a cup of tea? Effects of tea type and method of preparation. Food Chemistry, 125(2), 588–594. https://doi.org/10.1016/j.foodchem.2010.08.071↩︎

  7. Perva-Uzunalić, A., et al. (2006). Extraction of active ingredients from green tea (Camellia sinensis): Extraction efficiency of major catechins and caffeine. Food Chemistry, 96(4), 597–605. https://doi.org/10.1016/j.foodchem.2005.03.015↩︎

  8. Keenan, E. K., et al. (2011). How much theanine in a cup of tea? Effects of tea type and method of preparation. Food Chemistry, 125(2), 588–594. https://doi.org/10.1016/j.foodchem.2010.08.071↩︎

  9. Perva-Uzunalić, A., et al. (2006). Extraction of active ingredients from green tea (Camellia sinensis): Extraction efficiency of major catechins and caffeine. Food Chemistry, 96(4), 597–605. https://doi.org/10.1016/j.foodchem.2005.03.015↩︎

  10. Spiro, M., & Jago, D. S. (1982). Kinetics and equilibria of tea infusion: Kinetics of extraction of caffeine and theaflavins. Journal of the Science of Food and Agriculture, 33(4), 333–340.↩︎

  11. Spiro, M., & Siddique, S. (1981). Kinetics and equilibria of tea infusion: Part 1. Analysis and partition constants of the components of black tea. Journal of the Science of Food and Agriculture, 32(10), 1027–1032.↩︎

  12. Spiro, M., & Jago, D. S. (1982). Kinetics and equilibria of tea infusion: Kinetics of extraction of caffeine and theaflavins. Journal of the Science of Food and Agriculture, 33(4), 333–340.↩︎

  13. Perva-Uzunalić, A., et al. (2006). Extraction of active ingredients from green tea (Camellia sinensis): Extraction efficiency of major catechins and caffeine. Food Chemistry, 96(4), 597–605. https://doi.org/10.1016/j.foodchem.2005.03.015↩︎

  14. Spiro, M., & Jago, D. S. (1982). Kinetics and equilibria of tea infusion: Kinetics of extraction of caffeine and theaflavins. Journal of the Science of Food and Agriculture, 33(4), 333–340.↩︎

  15. Keenan, E. K., et al. (2011). How much theanine in a cup of tea? Effects of tea type and method of preparation. Food Chemistry, 125(2), 588–594. https://doi.org/10.1016/j.foodchem.2010.08.071↩︎

  16. Perva-Uzunalić, A., et al. (2006). Extraction of active ingredients from green tea (Camellia sinensis): Extraction efficiency of major catechins and caffeine. Food Chemistry, 96(4), 597–605. https://doi.org/10.1016/j.foodchem.2005.03.015↩︎

  17. Spiro, M., & Jago, D. S. (1982). Kinetics and equilibria of tea infusion: Kinetics of extraction of caffeine and theaflavins. Journal of the Science of Food and Agriculture, 33(4), 333–340.↩︎

  18. Perva-Uzunalić, A., et al. (2006). Extraction of active ingredients from green tea (Camellia sinensis): Extraction efficiency of major catechins and caffeine. Food Chemistry, 96(4), 597–605. https://doi.org/10.1016/j.foodchem.2005.03.015↩︎

  19. Spiro, M., & Jago, D. S. (1982). Kinetics and equilibria of tea infusion: Kinetics of extraction of caffeine and theaflavins. Journal of the Science of Food and Agriculture, 33(4), 333–340.↩︎

  20. Spiro, M., & Jago, D. S. (1982). Kinetics and equilibria of tea infusion: Kinetics of extraction of caffeine and theaflavins. Journal of the Science of Food and Agriculture, 33(4), 333–340.↩︎

  21. Spiro, M., & Siddique, S. (1981). Kinetics and equilibria of tea infusion: Part 1. Analysis and partition constants of the components of black tea. Journal of the Science of Food and Agriculture, 32(10), 1027–1032.↩︎

  22. International Organization for Standardization. (2019). ISO 3103:2019 — Tea — Preparation of liquor for use in sensory tests. https://www.iso.org/standard/73224.html↩︎

  23. Perva-Uzunalić, A., et al. (2006). Extraction of active ingredients from green tea (Camellia sinensis): Extraction efficiency of major catechins and caffeine. Food Chemistry, 96(4), 597–605. https://doi.org/10.1016/j.foodchem.2005.03.015↩︎

  24. Perva-Uzunalić, A., et al. (2006). Extraction of active ingredients from green tea (Camellia sinensis): Extraction efficiency of major catechins and caffeine. Food Chemistry, 96(4), 597–605. https://doi.org/10.1016/j.foodchem.2005.03.015↩︎

  25. Spiro, M., & Jago, D. S. (1982). Kinetics and equilibria of tea infusion: Kinetics of extraction of caffeine and theaflavins. Journal of the Science of Food and Agriculture, 33(4), 333–340.↩︎

  26. International Organization for Standardization. (2019). ISO 3103:2019 — Tea — Preparation of liquor for use in sensory tests. https://www.iso.org/standard/73224.html↩︎

  27. Spiro, M., & Jago, D. S. (1982). Kinetics and equilibria of tea infusion: Kinetics of extraction of caffeine and theaflavins. Journal of the Science of Food and Agriculture, 33(4), 333–340.↩︎

  28. International Organization for Standardization. (2019). ISO 3103:2019 — Tea — Preparation of liquor for use in sensory tests. https://www.iso.org/standard/73224.html↩︎

  29. Spiro, M., & Jago, D. S. (1982). Kinetics and equilibria of tea infusion: Kinetics of extraction of caffeine and theaflavins. Journal of the Science of Food and Agriculture, 33(4), 333–340.↩︎

  30. Keenan, E. K., et al. (2011). How much theanine in a cup of tea? Effects of tea type and method of preparation. Food Chemistry, 125(2), 588–594. https://doi.org/10.1016/j.foodchem.2010.08.071↩︎

  31. Perva-Uzunalić, A., et al. (2006). Extraction of active ingredients from green tea (Camellia sinensis): Extraction efficiency of major catechins and caffeine. Food Chemistry, 96(4), 597–605. https://doi.org/10.1016/j.foodchem.2005.03.015↩︎