Why does a film form on tea?
Why do some teas show it more?
Not all infusions have exactly the same composition.
The tea family, the amount of leaves, the processing, and the concentration of the infusion change the substances present in the cup.
The phenomenon has been particularly studied with black tea, where it can be especially visible.
A relatively concentrated infusion also provides more material that can participate in the interactions taking place on the surface.
This does not mean that you should systematically prepare your tea very light.
The goal remains first and foremost to obtain the aromatic profile that you enjoy.
But if a heavily dosed cup produces a significant film while a more balanced preparation with the same water produces less, the dosage may be one of the parameters to examine.
If you are unsure about your parameters, consult our guide to properly brewing the different types of tea .
How to know if your water is responsible?
You do not need to turn your kitchen into a laboratory.
The most useful test is also the simplest.
- Prepare the same tea with your usual water.
- Prepare a second cup with a different water, less mineralized or filtered.
- Use the same weight of leaves, the same amount of water, the same temperature, and the same brewing time.
- Compare the appearance and especially the taste of the two cups.
This last point is essential.
The goal is not solely to make a film disappear.
It is to find the water that allows the tea to express itself better.
A different water can change the clarity, but also the perception of bitterness, astringency, body, and certain aromas.
If your tea regularly seems too harsh or too bitter, water can therefore be one of the parameters to examine. You can also read Why is your tea bitter?
Before buying equipment or changing all your habits, simply prepare two identical cups with two different waters. You will immediately see if water plays an important role in your case.
Should you use bottled water?
Not necessarily.
Systematically changing water for each tea would be an excessive response.
If your tap water is pleasant to drink and produces good infusions, there is no reason to abandon it solely because a thin film occasionally appears.
However, if your water is very hard, has a strong taste, or quickly leaves limescale in the kettle, trying filtered or less mineralized water can be instructive.
Be careful also of the opposite excess.
Water extremely poor in minerals is not automatically ideal for all teas.
Minerals also participate in the way the cup is perceived.
The goal is therefore not to look for water completely devoid of minerals, but water sufficiently balanced to let the leaves express themselves.
Can a water filter help?
Yes, in certain situations.
A suitable filtration device can change the composition of the water and reduce certain elements responsible for its hardness or taste.
But not all filters work the same way, and their effectiveness changes with use.
It is therefore better to consider filtration as a practical experiment rather than an obligation for drinking good tea.
If you do not perceive any improvement in your cup, there is no need to make your daily preparation more complicated.
And lemon?
Acidity can change the formation of the film.
Adding lemon can therefore reduce it under certain conditions.
But this is obviously not a neutral solution.
A small amount of lemon can be enough to strongly change the taste and balance of a delicate tea.
If you naturally enjoyed your tea with lemon, no problem.
However, systematically adding lemon solely to obtain a clearer surface makes little sense if it masks the aromas you wish to taste.
Taste comes before aesthetics.
Why do traces sometimes remain on the cup?
The film can, over time, contribute to leaving marks on the walls of a cup or teapot.
These traces become more visible when deposits accumulate after several uses.
Regular cleaning naturally prevents this accumulation.
But if the film reappears after the next preparation in a perfectly clean cup, cleaning more will not necessarily remove the cause.
You will have cleaned the consequence.
Not necessarily the phenomenon that causes it.
What to remember
A thin film on the surface of a tea is not automatically a product defect.
It can result from interactions between the compounds extracted from the leaves and the minerals present in the water, especially when it is hard.
The phenomenon is different from the cloudiness that can appear throughout the infusion when a tea cools down.
If its appearance bothers you, the first test to perform is therefore not necessarily to change tea.
First try another water.
Prepare two identical cups and compare them.
You may discover something even more interesting than the disappearance of a film: how much water can transform the expression of the same leaf.
- The surface film is not necessarily a greasy residue.
- Hard water promotes its formation.
- Calcium and tea compounds play an important role.
- This phenomenon is not enough to judge the quality of a tea.
- It should not be confused with a tea that becomes cloudy when cooling.
- Comparing two waters with the same tea constitutes the simplest test.
To continue
Also discover why some teas become cloudy when cooling or consult our complete guide to properly brewing tea .
Find all our practical tips in the Cap sur le Thé Logbook .
Documentary references:
Scientific work dedicated to the formation of the tea surface film and the influence of the mineral composition of water, especially calcium and bicarbonates.
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