What Cold Brewing Really Does to Your Tea's Caffeine

Brewing & Storage｜Author：祥興茶行｜Published：2026-07-13

Cold water works like a selective filter: it holds back most of the caffeine and astringent catechins while letting the sweet amino acids through. And an overnight steep won't send the caffeine soaring.

Drop a tea bag into cold water, leave it in the fridge overnight, and by morning you have a glass of clean, sweet cold-brew tea. Many people choose cold brew because they've heard it "has hardly any caffeine, so you can drink it at night and still sleep." That is broadly right, and the reason is that cold water is selective about what it pulls out of the leaves: some compounds come out readily, others barely come out at all.

The short answer: same leaves, far less caffeine when brewed cold

Taiwan's Tea and Beverage Research Station (TBRS, under the Ministry of Agriculture) ran a direct comparison using Biluochun (碧螺春) green tea: the same leaves steeped in 4°C chilled water for 4 hours on one side, and in hot water for 5 minutes on the other. The cold infusion carried only about a third of the hot brew's caffeine (roughly 32%), while the amino acids responsible for fresh sweetness came out at nearly one and a half times the hot-brew level (about 180%) [1].

In one sentence: switch to cold brewing and caffeine drops sharply while the fresh, sweet compounds actually increase. What cold brewing changes is the ratio of compounds in the whole glass; less caffeine is just one part of that.

These figures come from a TBRS technical-extension trial. They are percentages relative to hot brewing, not absolute concentrations (mg/L), and no sample size or statistical testing was reported. Read them for the proportional trend, not as fixed values.

Other institutions found the same direction. A 2025 study in Food Chemistry measured Anji Baicha (安吉白茶; "white" in name, but actually a green tea): after 1 hour of cold brewing at 4°C, the infusion held 23.20 micrograms of caffeine per milliliter, against 40.90 for a 4-minute steep at 80°C, or 43.28% less for the cold brew [7]. A review from Japan's National Agriculture and Food Research Organization (NARO) also reports that cold water extracts about half the caffeine of hot brewing, and ice water less than 20% [2]. Three sets of green-tea measurements, from different origins and with different methods, agree: brew cold and the caffeine drops noticeably.

The chart compares specific time points: for caffeine, 1 hour of cold brewing against 4 minutes hot; for the two ester catechins, 3 hours cold against 2 minutes hot. Even with several times the steeping time, the cold brew still had less of the ester catechins than the hot brew [7]. The tea studied was Anji Baicha (a green tea), with n=3, so the numbers show a trend.

Cold water works like a filter

When the temperature drops, some compounds stay in the leaf and others come out anyway, because each compound needs a different amount of heat to dissolve. The first chart shows them splitting into two groups moving in opposite directions [1]:

Needs heat to dissolve (scarce in cold water) Caffeine, plus the ester catechins (EGCG and ECG). Catechins are the main source of astringency in tea, a kind of natural defense compound in the leaf, and the ester type is especially bitter and harsh. They dissolve slowly in cold water, so a cold-brew infusion carries noticeably less of them.

Dissolves well even when cold Theanine and the other free amino acids are the source of the infusion's fresh sweetness; think of them as the leaf's natural MSG. Along with them come the free catechins (EGC and EC). These release generously in cold water, and cold brewing can even extract more of them than hot brewing does.

The result is a cold infusion with less of the bitter compounds (caffeine, ester catechins) and more of the sweet amino acids, which is why cold brew tastes so sweet and smooth [1].

〔圖〕Diagram: cold water sorts tea compounds like a selective filter

Studies of extraction kinetics draw the same line. A 2006 green-tea extraction study divided the catechins into two groups: EGC and EC are little affected by water temperature and dissolve quickly even when it is low, while EGCG, ECG, and GCG need both time and heat. At 50–60°C barely any of them dissolves within ten minutes, and only high temperatures bring them out in quantity [8]. Caffeine sits in between: it rises with water temperature, but the study stresses that the increase is only slight [8]. This matches the TBRS numbers: at low temperature EGC and EC still come out, while most of the EGCG and ECG do not.

None of the three laboratory studies in this section (this 2006 green-tea study, plus the 2018 white-tea study and the green-tea temperature-matrix study below) actually brewed at 4°C: this one went no lower than 50°C [8], the temperature-matrix study no lower than 60°C [3], and the white-tea study did not test 4°C either [9]. They explain why low temperature is selective and why the ester catechins lag while the non-esters lead; for actual cold-brew numbers, rely on the cold-brew measurements above.

The Anji Baicha cold-brew experiment shows the same pattern: after 3 hours of cold brewing, EGCG (71.82 micrograms per milliliter) was still below a 2-minute hot brew (97.56 micrograms per milliliter), while EC exceeded the hot-brew level after just 8 minutes in cold water [7]. Esters lag and non-esters lead, consistent with the mechanism.

A white-tea study supports this from another angle. The 2018 white-tea brewing study found that above 80°C, the release of caffeine and EGCG climbs almost exponentially after the ten-minute mark [9], which shows it is low temperature that holds these two back. The study itself was about optimizing hot brewing and concluded that tasters preferred white tea brewed at 98°C. It did not test 4°C and does not vouch for the flavor of cold brew; all it supports is that temperature is the main switch [9].

Another green-tea brewing study compared different temperatures and found that ester catechins undergo a structural change at high heat (epimerization), so high and low temperatures yield different compound profiles [3]. This also supports the idea that the ratio changes.

Cold brewing changes more than the caffeine

The Anji Baicha study also measured taste, aroma, and liquor color, and cold brewing differed from hot brewing on all of them [7].

More fresh sweetness L-theanine, the source of umami, ran 9.2% higher after 1 hour of cold brewing than after 4 minutes of hot brewing. Cold brewing accumulates it steadily, while in hot brewing it starts to decline after 1 hour (heat makes theanine react with sugars and be lost) [7].

Bitterness held down The flavonol glycosides, which are astringent and also add yellow color, dissolve very slowly in cold water; even after 1 hour of cold brewing, their release falls short of 4 minutes in hot water. The study names this as the main reason cold brew does not turn astringent even after a long steep [7].

A different aroma Cold brewing accumulates floral, fresh alcohol aromatics (linalool, geraniol, α-terpineol and others), which rise markedly after the 1-hour mark; hot brewing brings out more of the beany, roasted, malty notes of pyrazines [7]. With the same leaves, cold brew leans floral and fresh, hot brew leans roasted and beany.

A greener, brighter liquor Cold brewing keeps more of the chlorophyll intact, so the liquor is greener and brighter; in hot brewing, heat breaks the chlorophyll down and the liquor browns toward yellow. Colorimeter readings showed the cold infusion growing greener over time while the hot one grew less green [7].

Two additional points. The soluble sugars behind the returning sweetness (glucose and sucrose) increase over time in both cold and hot brewing, so that part is not unique to cold brew. And the aroma data are relative and semi-quantitative, with n=3, from amino-acid-rich Anji Baicha (a green tea); they cannot be applied directly to Taiwanese oolongs or black teas.

Will steeping all night send the caffeine off the charts?

No. A review from Japan's NARO compiled dissolution curves for low-temperature extraction: after 1 hour in water at about 10°C, EGC, EGCG, and caffeine reach about 70%, 20%, and 50% of hot-brew levels respectively; in ice water near 0°C, caffeine falls below 20% of hot brewing [2]. Caffeine reaches a plateau after about an hour of steeping and barely increases after that; even at 16 or 24 hours it stays at around half the hot-brew level [2].

The Food Chemistry green-tea experiment found the same: during cold brewing, caffeine is released at less than half the rate of hot brewing, and it stops rising after the 1-hour mark [7]. Two different teams, two different green teas, the same conclusion.

These two datasets cover Japanese steamed green tea (sencha) and Chinese Anji Baicha (a green tea). Taiwan's ball-rolled oolongs and black teas differ in cultivar and leaf shape and may dissolve differently; the oolong in the next section is an example.

Temperature, not time, sets the caffeine level. An overnight cold brew tastes stronger and sweeter because amino acids and aromatics keep releasing; the caffeine does not rise with them. Whether overnight tea is safe is a separate question, covered at the end.

Oolong is the exception

Cold brew is not low in caffeine for every tea. A study comparing green, black, and oolong teas found that green and black teas were low in caffeine when cold-brewed, but cold-brewed oolong had the highest caffeine of all the methods tested [4].

The researchers attribute this to the oolong's shape: leaves rolled into tight, curled balls have a large surface area, and cold-brew steeping times are long to begin with, so caffeine is gradually extracted even at low temperature [4]. TBRS's cold-brew recommendations reflect this: 4 hours for green tea, 6 hours for Dong Ding oolong and Tieguanyin, and 10 hours for red oolong and black tea [1]. The longer the steep, the less the low temperature holds caffeine back.

Read this oolong counterexample for direction only: the study did not use a consistent leaf-to-water ratio across its three brewing methods, so its absolute values and percentages should not be quoted directly. What it shows is that leaf shape and steeping time affect the outcome, and that "cold brew means less caffeine" does not hold for every tea.

Is cold brew "healthier"? Look at the evidence, and mind food safety

People often equate "less caffeine" with "healthier and easier on the stomach." That is too big a jump.

The NARO review raises a paradox: the immune-related effects of EGC and the anti-stress effects of theanine show up in cold brew partly because cold brew contains less of the EGCG and caffeine that would suppress them [2].

These effects come mostly from animal models such as mice, not human clinical trials. They are mechanistic hypotheses plus animal evidence, not health benefits of drinking cold-brew tea, and they make no therapeutic claims. The current evidence does not support using cold brew to stay healthy or treat illness.

Food safety deserves more attention, and here Taiwanese and American institutions give different advice:

TBRS (Taiwan): cold brewing "in the refrigerator" is sufficient, a comparatively relaxed approach [1].

SDSU Extension (a U.S. state-university extension service): far more conservative. It treats "6–12 hours of refrigerated steeping" as common practice, but its safety advice is to first heat the tea to a specified temperature to kill pathogens once the leaves are in the water (about 63°C/145°F for 2.5 minutes, or about 72°C/161°F for 1 minute, to destroy Salmonella, E. coli, and Listeria) and then refrigerate. It also warns against leaving the tea at room temperature and against vacuum, oxygen-free sealing (low-oxygen, insufficiently acidic conditions raise a botulism concern) [6].

Cold brewing involves no heat sterilization at any stage. A study of cold-brew coffee found that 2 of 23 samples (about 9%) had markedly elevated microbial counts, and one of them tested positive for Bacillus cereus after 5 days of refrigeration [5]. Cold-brew coffee is not tea, so this is only indirect evidence from a similar long, low-temperature extraction, but the logic is the same: without heat, there is one less sterilization step.

In practice: for home cold brew, keep it refrigerated throughout, never leave it at room temperature, finish it the same day, and don't use vacuum oxygen-free sealing. For extra safety, follow the American approach: heat the tea once the leaves are in the water, then refrigerate it to steep.

The conclusion, in one cup

1. Cold brew does have less caffeine; the key is that the ratio changes. Cold water holds back most of the caffeine and the bitter ester catechins while letting through sweet theanine and floral aromatics. Three sets of green-tea data, from TBRS, Japan's NARO, and the 2025 Food Chemistry study, all show this (cold-brew caffeine at roughly 30–50% of hot brew) [1][2][7].

2. An overnight steep won't send the caffeine soaring. Caffeine plateaus after about an hour and does not increase with longer steeping, as two different green-tea studies agree. Temperature, not time, sets the level (green-tea data; other teas may differ) [2][7].

3. Less is not zero, and it is not the same as healthy. Ball-rolled oolong can still release plenty of caffeine over a long steep [4]; the health effects come mostly from animal studies and involve no therapeutic claims; for food safety, keep it refrigerated throughout and finish it the same day, and heat-sterilize first if you want extra safety [1][5][6].

To learn how water temperature affects a cup of tea, see our "Water Temperature Guide"; for where the bitter catechins come from, see "Catechins and the Roast."

References

1. 戴佳如、邱喬嵩、陳國任、楊美珠（2015）。不同茶類之最佳冷泡條件。茶情雙月刊，第 79 期，第 2–3 版。農業部茶及飲料作物改良場。https://www.tbrs.gov.tw/upload/tres/files/web_structure/2046/1040624-5.pdf
2. Monobe, M. (2018). Health Functions of Compounds Extracted in Cold-water Brewed Green Tea from Camellia sinensis L. Japan Agricultural Research Quarterly (JARQ), 52(1), 1–6. https://www.jircas.go.jp/sites/default/files/publication/jarq/52-01-01_001-006_MONOBE.pdf
3. Jin, Y., Zhao, J., Kim, E. M., et al. (2019). Comprehensive Investigation of the Effects of Brewing Conditions in Sample Preparation of Green Tea Infusions. Molecules, 24(9), 1735. https://doi.org/10.3390/molecules24091735
4. Lantano, C., Rinaldi, M., Cavazza, A., Barbanti, D., & Corradini, C. (2015). Effects of alternative steeping methods on composition, antioxidant property and colour of green, black and oolong tea infusions. Journal of Food Science and Technology, 52(12), 8276–8283. https://doi.org/10.1007/s13197-015-1971-4
5. Claassen, L., Rinderknecht, M., et al. (2021). Cold Brew Coffee—Pilot Studies on Definition, Extraction, Consumer Preference, Chemical Characterization and Microbiological Hazards. Foods, 10(4), 865. https://doi.org/10.3390/foods10040865
6. Braun, C. (SDSU Extension). How to Make Cold Brewed Teas Safely. South Dakota State University Extension. https://extension.sdstate.edu/how-make-cold-brewed-teas-safely
7. Yang, X., et al. (2025). Effects of cold and hot brewing on the taste, aroma and colour of green tea (Anji Baicha): a metabolomic and sensory study. Food Chemistry, 479, 143788. https://doi.org/10.1016/j.foodchem.2025.143788
8. Labbé, D., Tremblay, A., & Bazinet, L. (2006). Effect of brewing temperature and duration on green tea catechin solubilization based on quality and quantity of tea infusions. Separation and Purification Technology, 49(1), 1–9. https://doi.org/10.1016/j.seppur.2005.07.038
9. Pérez-Burillo, S., Giménez, R., Rufián-Henares, J. A., & Pastoriza, S. (2018). Effect of brewing time and temperature on antioxidant capacity and phenolic compounds of white tea. Food Chemistry, 248, 111–118. https://doi.org/10.1016/j.foodchem.2017.12.056