Does your curiosity about cold-brew tea go beyond just the amazing flavor? If so, you’ve come to the right place! Don your science caps because we are about to dive into the science of temperature, solvents, and extraction! Or, to put it simply- what difference does the temperature of water make on the antioxidant levels of different teas?
Read on to learn…
- How does water temperature affect tea taste?
- What are the two main cold brewing methods?
- Cold Brewing Black vs Green vs Oolong vs White Tea: Which has the most antioxidants?
- Cold Brewing Red vs Green Rooibos: Which has the most antioxidants?
Welcome to Part 10 of our Antioxidants series! This ever-expanding collection of posts sheds some scientifically-robust light on antioxidants and antioxidants in tea in particular.
What difference does water temperature make on tea flavor?
Excellent question, and the answer is: a huge difference!
The first thing to know: A solvent is a fancy term for a liquid used to dissolve components added to it to form a solution.
In this case, your tea water is acting as the solvent to extract (dissolve) the many naturally-occurring chemicals found in tea leaves. When these dissolve into the water you get a cup full of micronutrients, nutritives, and antioxidants. We like to call this solution “tea” - you may have heard of it!
Depending on the temperature, you’ll get different flavor profiles as the tea leaves interact in different ways with the water:
- Cold brewed teas are often smoother tasting, slightly sweeter, and less bitter.*
- Hot brewed teas are often stronger and more bitter, with more tannins and caffeine released (caffeine is incredibly responsive to heat, and very soluble).
* If your cold brew is still bitter and not very smooth, odds are it was made as a simple iced tea, where it was brewed hot then iced rather than just being steeped in cool water where the compounds are slowly coaxed out of the leaves to create an incredible flavor profile.
Temperature is a major determinant of what gets extracted. For example, tannins are a compound found in teas that are generally responsible for the bitter, astringent flavor. The more you brew a batch of green or black tea the more bitter it becomes because of the increased tannins.
So, that’s all about flavor - but how does temperature affect antioxidant status? Is your cold brew sencha just as health-conscious as your steaming mug?
Classically brewed iced tea in our Mist style Pitcher This iced tea pitcher
How to Brew Tea for Maximum Antioxidants
Before moving to specific studies, let’s talk brewing. Being the avid tea drinkers you all are, you are likely familiar with traditionally brewed tea (hint: this is the one that involves pouring hot water from the kettle over the leaves and letting them steep for a few minutes, aka healthy fast food!).
Cold brews tend to have some pretty solid antioxidant action, and lower caffeine content. Heat helps extract those caffeine chemicals called xanthines (Lantano, 2015).
As always, there are exceptions to the rule though: Although caffeine content is generally less in cold brews, oolong defies the rule.
In the above study by Lantano et al., cold brews extracted the least amount of caffeine compared to traditional and iced brews.
Iced brews had the highest amount of caffeine between the groups in green and black teas, but cold brewed oolong had the most caffeine compared to oolong brewed in other methods. The authors suggest that the large surface area of the oolong leaves plus the extended length of time in cold brew likely played a role. So watch your oolong carefully!
But what are the main cold brew methods?
- The Straight n’ Narrow (aka True Cold Brew): Cold brews are long infusions. The benefits come from a combination of water temperature + time (with a big emphasis on this!). Pour room temperature or cool water over your leaves, then refrigerate for several hours (3-12 is the most common). This method is great to prepare just before bed. Simply prep, sleep, and wake to perfectly brewed tea! All good things to those who wait…
- The Cheat (aka Classic Iced Tea): This is the method that shortens the time but still reaps many of the long-infusion cold brew benefits - minus some of the velvety smoothness that cold brewing is famous for. In this method you start out with the traditional method by pouring hot water over the leaves. That’s the bait, now it’s time for the switch! Add some ice and allow to cool. This stops the heat action, allows some cold infusion to occur, and the perk is that your tea will be ready in a manner of minutes! The authors weren’t very clear on this point, but it seems like the effect lies in the shocking of the temperature from hot to cold rather than a slow cool-down.
So, pick your favorite, and let’s look at how different tea types and their antioxidant levels respond to the various hot vs cold brewing methods.
Iced tea is the happiest way to still enjoy tea during sweltering summer days when a hot cuppa is the last thing you want...
Cold vs Hot Brew Black, Green and Oolong Tea
Polyphenol Levels & Antioxidant Power in Hot vs Iced Green & Black tea
Time to dive into the science of what exactly happens to your black and green teas when you brew them in different ways.
In a recent Indian study, the authors looked at the antioxidant status in green and black tea brewed in hot or cold water (Das, 2017). They concluded:
- Black teas showed little difference in polyphenols whether they were brewed hot or cold, but green tea did differ significantly.
- The total polyphenol count in cold brewed green tea was higher than in hot brewed green tea, while both brews contained more polyphenols than either preparation of black tea.
In other words, cold brew green tea is the way to go for polyphenols! And green tea beats out black tea across the board for antioxidant levels.
In another study that compared green vs black vs oolong tea, there was no notable difference in Total Phenolic Content between the different types of teas. The Straight n’ Narrow (aka True Cold Brew) method presented the highest amount of polyphenols, followed by the Cheat iced method, while the traditional (hot) brew had the lowest (Lantano, 2015).
How Stable are the Antioxidants with Different Brewing Methods? Does Heat Degrade Them?
Because antioxidants degrade over time, and this can be sped up with heat, it’s important to measure this. The test to measure this is called the FRAP assay, aka Ferric Reducing Ability of Plasma (this sounds to me like a good name for an over-energetic cat, but I digress). FRAP is one of the many assays used to evaluate antioxidant action (Shahidi, 2015).
In this same study, they measured green vs oolong vs black teas to see how stable the antioxidants were with heat and time, using the three different brewing methods (Lantano, 2015). Here’s what they found:
- Green tea had the highest FRAP values of all three teas, but the values were consistent across brewing methods. This means that the antioxidants in green tea are heat stable regardless of brewing method.
- Oolong had the lowest FRAP values, demonstrating heat sensitivity, and degradation of antioxidants over time.
- Iced black tea had a higher FRAP value than hot brew, with no significant differences between the two iced tea brewing methods (the Straight n Narrow vs the Cheat).
Flavonoids in Black vs Green Tea, Hot vs Cold Brewed
Going back to the Indian study, they also evaluated flavonoid content. They found that temperature did not create a significant difference of flavonoids in black tea but there was a difference in green tea where, similar to the polyphenols, the cold brew also demonstrated a higher amount of flavonoids (Das, 2017).
The authors stated that both the cold brewed green and black teas contained “a good amount of flavonoids… and polyphenolics” (Das, 2017). (For those of us scratching our heads, “polyphenolics” is a fancy word for polyphenol compounds.)
Intriguingly, despite the higher counts of flavonoids and polyphenols in cold brewed green tea, the authors also found that the antioxidant activity as a whole is comparable to the hot brewed tea.
Furthermore, heat stability and antioxidant breakdown did not appear to be a factor as the authors did not mention any concerns on this.
This is good news for us! Hot or cold, we’re still getting great antioxidant action!
Which Cold Brew Method Yields the Most Antioxidants for Green, Black, and Oolong Teas?
Jumping back to the Italian study by Lantano et al., they analyzed brewing methods for a range of teas to see how antioxidant levels varied. They measured:
- Sencha Needle unfermented green tea
- Tung Ting semi-fermented oolong (also known as Dong Ding, this is a rolled High Mountain oolong from Taiwan)
- Orange Pekoe Flowery fully-fermented black tea
They found that the Cheat brewing method from above yielded the highest amounts of antioxidants for each category analyzed (except Theophylline, which was constant across all brews) (Lantano, 2015).
They were specifically measuring these parameters (I’ve written about most of these, click their names to learn more about these different antioxidants and what they do!):
However, when they measured TOTAL antioxidants and antioxidant capacities, they found that the Straight ‘n Narrow approach (i.e. True Cold Brew) was best for the green and black teas. The authors believe this has to do with the amount of time the leaves are exposed to the water, allowing for maximum extraction (Lantano, 2015). The exception was EC, which interestingly was not found in the cold brews at all!
This is a great reminder of how important it is to look at the entire picture - as it can sometimes be very different from when we just zoom in on one component.
Which Brewing Method Yields the Most Antioxidants for White Tea?
When researchers evaluated hot vs. cold brewing for green, black, and white teas they found that the temperature did not make a difference in antioxidant activity as a whole, except in white tea which had greater activity as a cold brew, using either cold brew method (Venditti, 2010).
It appears that while antioxidants may have higher counts in cold brew teas (typically green and white), the actual antioxidant action is still comparable to hot brewed teas.
The number and types of antioxidants that are increased in cold brew tea will offer health benefits according to which ones are present. To learn more about what different antioxidants do, read more here.
Hot & Cold brewed Rooibos: Phenolic Profile & Antioxidant Capacity of Red vs Green Rooibos
Enough with talking about teas from Camellia Sinensis, time to move on to my favorite tisane: rooibos!
Red and green rooibos were examined in another Italian study to see how brewing temperatures affected their antioxidant levels, ORAC, and total polyphenol content (Damiani, 2019).
They found notable differences between the red and green versions! While red rooibos performed best as a traditionally brewed tea in hot water,* green rooibos had better antioxidant scores as a cold brew! This is due to the fermentation of red rooibos.
* They also compared a preparation method of boiling, which extracted the most antioxidants, but since boiling is uncommon for preparing most teas (you might simmer some hardier herbs for a concentrated extraction, or if you’re making a masala chai), it’s not very applicable to the vast majority of us!
Green rooibos demonstrated a higher ORAC score as both a cold brew and a hot brew compared to red rooibos, with the cold brew for green yielding the greatest antioxidant capacity (Damiani, 2019).
The same results were observed for the total polyphenols - cold brewed green rooibos wins, hands down!
The same study also took stock of antioxidant categories:
Image source: Damiani, et al. (2019)
Their results for total antioxidants for green vs red rooibos:
- Overall winner: Cold-brew green rooibos. Across all categories cold-brewed green rooibos outscored both hot-brewed and cold-brewed red rooibos.
- Hot-brewed red rooibos is better than cold-brew: Hot-brewed red rooibos scored higher in all categories (except resveratrol) compared to cold-brewed red rooibos. Fascinating!
Does boiling water destroy antioxidants in rooibos?
As for heat, the cold-brewed rooibos extracted certain heat-sensitive compounds compared to boiled rooibos (the 3rd extraction method they tested), but the authors did not note any concern for hot-brewed rooibos destroying antioxidants.
It appears that for the antioxidants to be destroyed, the tea would have to be boiled consistently for a length of time. (This was true for both red and green rooibos.) Breathe a sigh of relief - your normal rooibos brewing method isn’t damaging your antioxidants!
So folks, the verdict is in! Take the long way ‘round by using a cold brew method for your green rooibos and enjoy your red rooibos hot and you’ll get the best of both worlds!
A Note From the Herbalist
Whew, that was a science-heavy post! But, I hope it was useful. :-)
The over-simplified moral of the story: you can’t go wrong with cold brew.
As a rule I tended towards herbal tisanes - infusions of herbs rather than C. sinensis. I make exceptions on occasion, as green tea has excellent health benefits and a pleasant taste, but I’ll always be a tisane gal.
I have made sun tea and iced tea, and cold-brew coffee in the past, but the legitimate method of cold brewing was new to me. I decided to give it a shot with a combination of our The Purist Rare Purple tea and the Silver Needle white tea I had on hand. I had been drinking them but, due to user error (I get distracted and over-steep my tea, especially when writing articles!), I generally ended up with a bitter beverage.
So, into the quart mason jar they went, I added cool filtered water, then stored it in the fridge. In the morning I awoke to a lovely surprise - I had brewed the smoothest, most flavorful tea I had ever tasted! Flavor notes abound! The mouth-feel is indescribably good, and I just can’t get enough!
I’ve been brewing a quart every night to sip through the day, and I highly recommend giving it a try. Simply delicious!
Now you've learned about cold brewing, give it a try! Plus, whenever you buy a bundle we plant 1 tree, saving 1 ton of CO2
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Read the last post in this series:
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Read the Rest of Our Antioxidants in Tea Series
➔ Part 1: What Are Antioxidants and How Do They Work?
➔ Part 2: All About Antioxidants: Q&A with the Herbalist
➔ Part 3: How Are Antioxidants Measured? ORAC Scores and How Much You Need Per Day
➔ Part 4: Busting the Matcha Myth: Does matcha really have 137 times more antioxidants (EGCG) than green tea?
➔ Part 5: Antioxidants in Green vs Black Teas: What's the Difference?
➔ Part 6: Antioxidants in Rooibos, Honeybush & Chamomile: What Do They Actually Do?
➔ Part 7: Antioxidant Benefits of Yerba Mate, Moringa, & Tulsi
➔ Part 8: Most Common Antioxidants in Green Tea
➔ Part 9: Purple Powerhouse: Antioxidants in Purple Tea & Their Health Benefits
References & Further Reading for Cold Brew Antioxidants
Das, C., & Chatterjee, S. (2017). Evaluation of Antioxidant Status in Cold Brewed Tea with Respect to Hot Decoction: Comparative Study Between Green and Black Varieties. International Journal of Pharmacognosy and Phytochemical Research, 9(07). https://doi.org/10.25258/phyto.v9i07.11163 Retrieved from https://www.researchgate.net/publication/319352099_Evaluation_of_Antioxidant_Status_in_Cold_Brewed_Tea_with_Respect_to_Hot_Decoction_Comparative_Study_Between_Green_and_Black_Varieties
Damiani, E., Carloni, P., Rocchetti, G., Senizza, B., Tiano, L., Joubert, E., de Beer, D., & Lucini, L. (2019). Impact of Cold versus Hot Brewing on the Phenolic Profile and Antioxidant Capacity of Rooibos (Aspalathus linearis) Herbal Tea. Antioxidants (Basel, Switzerland), 8(10), 499. https://doi.org/10.3390/antiox8100499 Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6826389/
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 Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4648929/
Shahidi, F., & Ambigaipalan, P. (2015). Phenolics and polyphenolics in foods, beverages and spices: Antioxidant activity and health effects – A review. Journal of Functional Foods, 18, 820–897. https://doi.org/10.1016/j.jff.2015.06.018 retrieved from https://www.sciencedirect.com/science/article/pii/S1756464615003023
Venditti, E., Bacchetti, T., Tiano, L., Carloni, P., Greci, L., & Damiani, E. (2010). Hot vs. cold water steeping of different teas: Do they affect antioxidant activity? Food Chemistry, 119(4), 1597–1604. https://doi.org/10.1016/j.foodchem.2009.09.049 retrieved from
Emmanuel Mfotie Njoya, in Cancer (Second Edition), 2021. Medicinal plants, antioxidant potential, and cancer. https://www.sciencedirect.com/topics/medicine-and-dentistry/ferric-reducing-antioxidant-power-assay