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I have been drinking tea excessively for many years now. Once in a while, I have tried to prepare tea bags with cold water for different reasons, but the outcome never was what I wanted it to be.
There are good reasons to use hot water to make tea, but brewing tea with cold and ice-cold water does have it’s place. Here, I want to share why brewing tea bags with cold water has its difficulties.
SHORT ANSWER – Why Do Tea Bags Not Work In Cold Water?
With cold water, the infusion of the tea bag is slower and less compounds are extracted from the tea leaves. Tea brewed with cold water contains less caffeine, tannins, catechin, flavonoids, polyphenols and other compounds. A single tea bag can not be brewed effectively and safely with cold water.
There’s a lot more information to share on this topic. Throughout this post I explain the mechanics and differences between preparing your tea with hot and cold water.
If you want to try actually cold-brewing tea, you should use loose leaf tea (rather than tea bags) and try a cold brew tea bottle with a built-in filter. There’s one I love to use myself that you can find on amazon:
In Cold Water Tea Infuses Much Slower Compared To Hot Water
When brewing tea with cold water, the molecules in the tea leaves move slower and large molecules such as proteins or tannic acid are unable to overcome barriers. This process is called extraction. Most flavor, including bitter compounds, are extracted at high temperatures with boiling water.
The infusion of tea leaves in water is essentially the movement of molecules from the tea leaves into the water. In chemistry, this process is known as extraction, and it is the fundamental basis of making good tea.
The temperature plays a huge role in this process, because molecules are moving faster at higher temperatures. This also allows molecules to overcome barriers and get out of the tea leaves.
Especially larger molecules like proteins or even some smaller molecules like tannic acid will not get extracted from the tea leaves easily when using cold water. These require hot or boiling water.
Of course, this can have both a positive and a negative impact on the tea you brew. But more often than not, tea bags are produced to be infused at precise temperatures for a set amount of time.
Tea inside tea bags is more often than not fanning or dust, which are powdered tea leaves. Because of this, the tea leaves have a large surface area and will infuse quickly.
Manufacturers exploit this mechanic and use a minimal amount of tea per tea bag that only works well when brewing with hot water for a set amount of time. You would need more tea and, ideally, loose leaf tea for the best results for brewing with cold water.
For example, Darjeeling black tea in a regular tea bag will infuse well when brewing with boiling water for 3-4 minutes. With cold water, you get close to no flavor at all. Besides the infusion rate, there’s another reason for that.
Some Flavor Compounds Do Not Dissolve Well In Cold Water
Cold water is not able to extract as much caffeine, catechin, polyphenols, proteins, flavonoids from the tea leaves. The amount that can be extracted is very dependent on the water temperature. This is due to the solubility of most compounds increasing exponentially with the temperature.
It is a general rule that compounds are more soluble in hot or boiling water than in cold water. This is due to the fact that liquids are able to hold more molecules in solution at higher temperatures.
What this means for your tea is that some compounds are much less soluble at room temperature or below than they would be when brewing with hot water. There are both positive and negative effects to this.
For example, you’d never prepare a green tea with boiling water, right? That is because green tea has a lot of bitter compounds that have not been degraded through oxidation (to black tea) or roasting (often found with oolong tea).
Molecules like various proteins, flavonoids, polyphenols, caffeine, catechin and many other compounds are not dissolved easily in water at low temperatures.
Other molecules are still soluble quite well at low temperatures. There is always a trade-off. You will get less flavor out of the tea leaves, but that may help with the bitterness of a tea.
What you need to do when brewing tea with cold water is simply using more tea leaves. That way, more compounds in total than can be dissolved while still getting less bitter compounds and caffeine.
There’s good reasons to try cold brewing but also some important things you need to be aware of. The most important ones are listed further down in this article.
Less Tannins In Tea Brewed In Cold Water Makes It “Gentle”
Tannic acid is a common compound found in tea responsible for a dry mouthfeel and bitter taste. In hot water, tannic acid is very soluble. To lower the solubility, water at room temperature is not cold enough. You will need to use ice-cold water to exclude most tannins from your tea experience.
Tannic acid is a compound that is found in all kinds of tea made from Camellia Sinensis and can be found in many other places with a predominant example being red wine.
Even at room temperature, tannic acid remains somewhat soluble in water and will thus remain in your tea infusion. The dry mouthfeel will be much less noticeable at these brewing temperatures, though.
The least tannins will be dissolved when cold brewing the tea with ice-cold water. If you choose to make tea with ice cold water, many flavors (including bitter taste) will mostly disappear.
Depending on the tea you want to brew, tannins may play a large role in giving the tea a full-bodied and round taste. That is especially the case with black tea and pu erh tea.
If you want your tea to be full-bodied, you shouldn’t use cold water. If you want your tea to be gentle and light, then cold brewing is the way to go.
There Is A Lot Less Caffeine In Tea Made With Cold Water
Caffeine is more than 41 times more soluble in boiling water and 12 times more soluble in hot water when compared to water at room temperature. Cold water will yield a tea that contains a lot less caffeine and allows for a cup of tea in the late evening. Tea with less caffeine is also less bitter.
Caffeine is a compound where the difference in solubility is extremely high between cold, hot or boiling water. Depending on taste and time of day, you should keep this in mind.
At room temperature (77 °F, 25 °C), a cup water (about 237 ml) will hold up to 3.79 grams of caffeine while the same cup can hold 47.32 grams at 176 °F (80 °C) and 157.57 grams at 212 °F (100 °C).
This does not mean that these amounts of caffeine will be dissolved when making tea! But these numbers can get you an idea of how the solubility increases rapidly when raising the temperature.
Consider that hot water can dissolve more than 12 times the caffeine than water at room temperature can. And caffeine is more than 41 times more soluble in boiling water than room temperature water.
If you want a strong caffeinated cup of tea, you should not brew your tea with cold water. But if it’s late in the evening, you could try a cold brew and increase the quality of your sleep.
Powdered Tea In Tea Bags Is Not Well Suited For Cold Brew
Most tea bags contain lower-quality tea leaves in the forms of dust and fannings. This is essentially broken up tea leaves that are supposed to be infused once and quickly.
This type of tea is either made intentionally through a process called Crush-Tea-Curl (CTC) or by using the broken tea that would otherwise be wasted during loose leaf tea production.
The positive impact of cold-brewing tea is reduced due to the high surface area of broken and powdered tea leaves. Brewing tea with cold water will always require more tea leaves than brewing with hot water.
Compounds normally not extracted from the whole tea leaves can be dissolved faster and easier when using tea bags. That’s why the tea will get much more bitter when using tea bags instead of loose leaf tea, even though you are using cold or ice-cold water.
Cold Water Does Sufficiently Kill Microorganisms In The Tea
Microorganisms are a natural occurrence with tea. As tea can be stored for extended periods of time, the bacteria, germ and mold growth on the tea leaves should be considered.
In order to prepare tea safely, a water temperature above 140 °F (60 °C) is recommended. I’d choose a temperature a little above that, as the water will cool quickly when added to a cup or teapot.
If you get your tea from a reliable source and the tea leaves are not that old, brewing the tea with cold water will be fine. Just don’t brew decade-old Pu Erh tea with cold water!
Some Tea Bags Should Never Be Prepared With Cold Water
Some teas should never be brewed with cold water. Depending on the leaf material, additives, and aroma used in the tea, boiling or at least hot (176 °F, 80 °C) water may be necessary for the tea to be safe to drink.
This includes a lot of aromatized teas, herbal teas and teas based on bamboo. To be sure, please read the instructions on the packaging or ask the person behind the counter.