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Whenever I am brewing a cup of tea, some foaming will occur. I have wondered many times over the years why that is and if I should care if the tea does foam.
With some understanding of the mechanics behind foaming and the formation of bubbles, I did some research on what is in the tea that causes this phenomenon. Here I want to share my findings with you.
SHORT ANSWER – Why Is Tea Foaming?
The foaming of tea is caused by amphiphilic compounds contained in the tea leaves that are extracted into the water during the brewing. These compounds create foam in a very similar way to soap creating bubbles and foam. Foaming tea is generally not a cause for concern as it is not unusual for tea.
So the cause for foaming tea is natural and you should normally not be concerned when brewing and drinking foamy tea. But what information can you derive from the formation of foam? Should you care?
How Bubbles And Foam Are Formed
The foam that is commonly formed on the surface of freshly brewed tea is very similar to the foam and bubbles that are formed with soap water. But the foam is formed by compounds different from soap.
General Concept Of Foaming
To start with, I want you to understand how foam and bubbles are formed generally. You may have learned at some point that soap contains amphiphilic molecules.
While this sounds complicated, the meaning of this is quite simple. There are molecules of which one end likes water (hydrophilic) and one end that does not like water (hydrophobic).
These molecules will form natural structures so that the ends that don’t want to be in contact with water are touching each other. On a large scale this does form bubbles and foam.
This concept does not only work with soap but also works for many other molecules. This includes many compounds that are included in tea naturally.
Such compounds that are able to form bubbles and foam are contained in each and every tea you have ever brewed but will be more prominent in some teas and depend on how you brew the tea.
Compounds In Tea Cause Foaming
Many compounds in your tea will cause foam to form on the surface. It’s not something rarely found in tea but rather compounds found in all plant material and in all teas no matter how they are processed or prepared.
While researching I have come across numerous potential candidates that will be responsible for the formation of foam on your tea. The most common and realistic are the following.
- Amino Acids – Amino acids are compounds that are found in all lifeforms and thus also in tea. The amount of soluble amino acids has a major influence on the amount of foam formed on the surface of the brewed tea.
- Denatured Proteins – Proteins are larger molecules made up of amino acids. Higher concentrations of denatured proteins will thus also increase the amount of foam that is formed.
- Fatty Acids – Another category of molecules that are contained in tea are fats and fatty acids. Fatty acids are ideal for the formation of foam in tea and resemble the molecules in your soap the closest.
A lot of these compounds are inside tea leaves and depending on how you brew your tea, these will cause a few bubbles or a full layer of foam to form on the surface of your tea.
How The Foam Is Created
Other than these compounds, the formation of foam needs air to be inserted into the liquid. There are some main ways that air is commonly introduced to the infusing tea. I have listed the most common ones here.
- Trapped Air – Air can be trapped inside the tea leaves you use or inside the tea bag. If the air is released below the water surface and enough amphiphilic (see above) compounds are close, many small bubbles are formed.
- Pouring The Water – Depending on how you poured the water onto the tea leaves or tea bag there is a high chance that you have pushed air into the mixture. Some of the air will stick to the tea, the tea bag and the walls of the brewing vessel and soon become foam.
- Dissolved Gas – Gas can be dissolved in water too! For example, water will generally contain some elemental oxygen. Some of the dissolved gasses can escape and form a foam on the tea, too.
What Influences The Amount Of Foam
The amount of foam that is formed on your tea depends largely on the amount of foaming compounds dissolved and how much gas is introduced to the mixture. Again, here is a small list of things that influence the amount of foam formed.
- Water Temperature – The amount of foaming compounds dissolved in the tea you make is very dependent on the water temperature you use. How exactly water temperature affects the amount of flavor and other compounds dissolved in your tea was explained thoroughly in a previous post.
- Type Of Tea – While every tea will contain foaming compounds, there are natural variations in the concentrations of foaming compounds. Heavily roasted teas, for example, will contain fewer of such molecules.
- Broken Or Full Leaf Tea – While this does not affect the total concentration of these compounds in the tea leaves, this changes the amount that gets extracted. Broken tea leaves have much higher surface area and will allow for more foaming compounds to get dissolved in the tea faster because of that.
- Additives In The Tea – Many teas contain some additives. Some of the most popular teas, Earl Grey, contains an additive that not only makes it taste like soap, but also foams a lot more. For more information on soapy flavors in tea, take a look at this post.
There are a lot more things that influence the amount of foaming, but I would consider these the most important for you to know. Of course, longer steeping times, stirring and shaking will cause more foam to form.
How Microwaving The Water Causes White Foam On Your Tea
Many people are heating the water they use to make tea directly in the microwave and add tea in the form of a tea bag afterward. I have commonly been asked why this causes a film of thick white foam to form on the surface of the tea.
The reason for this is the overly heated water. Water can be heated past its boiling point quite easily. The bubbling when boiling water can only happen when there is some starting point for the transfer from liquid to gas.
If the cup you are using to make tea is not coarse and does not have any dirt particles on the inside, the water will not be able to boil properly. The first so-called nucleation point for water to turn into gas at, is the tea bag.
For this reason, many small bubbles of gas are formed as the tea bag touches the surface of the superheated water. This will cause a thick film of tiny bubbles or foam.
Should You Be Concerned About Foam On Your Tea?
As stated in the introduction and from the information provided throughout this article you should not that the foam on tea is completely natural and nothing to worry about.
What Foaming Tells You About The Tea
If you brew yourself a nice cup of tea and some foam is forming on the surface of it, you now know something about your tea. You know that your tea contains good amounts of denatured proteins, amino acids and fatty acids.
None of these should make you concerned in any way as all of them are natural content of any plant. The amount of foaming will further tell you how intact the tea leaves are, though.
If the tea leaves are fully intact, fewer foaming compounds will be released into the resulting tea and cause less foam to form because of that.
If more foaming occurs, there’s a good chance that you are dealing with broken tea leaves or tea that was intensely rolled during processing. That would be common with any oxidized teas like black tea and darker oolongs.
When You Should Be Concerned
You should only be concerned about the formation of foam if it seems unnatural. It is very hard to control the actual processing of tea and the tea may contain traces of actual soap or other foreign substances.
If you notice any unknown contents, weird-looking tea leaves, mold or if your tea has some weird off-taste, you should be concerned. This happens very rarely and is not directly correlated with foaming tea.
There’s a lot more to learn about tea! If you are looking for a good place to start, I highly recommend the book Tea: History, Terroirs, Varieties. You can check its current price on Amazon here.