There is scale in my kettle and a film on my tea

In short

Two related problems with one root. Scale is dissolved mineral coming out of solution when water is boiled; the surface film is a separate effect of hard water on the tea itself. Descaling fixes the first and only partly helps the second.

Likely causes, in order

Most likely first. Answer the question under each one before moving on — several of these look alike in the cup and are told apart only by what was done to the leaf.

1. 1. Hard water, and no descaling routine

   Water chemistry

   Check: Do you live in a hard-water area, and when did you last descale the kettle?

   Fix: Descale monthly with citric acid or white vinegar, then boil and discard two kettles of plain water. Scale does not harm the tea directly, but a heavily scaled element heats unevenly and a temperature-controlled kettle loses accuracy.

2. 2. The surface film is hard water reacting with the tea, not scale

   Water chemistryInferred by TeaHQ, not established

   Check: Is the film iridescent and does it break into patches when you stir, rather than being visible flakes?

   Fix: That film is not descaling debris and will not go away with a clean kettle. Filtered water removes it, and it is the same change that stops hard water flattening aroma.

3. 3. Re-boiling water that has already concentrated

   Water chemistry

   Check: Do you top up and re-boil rather than emptying and refilling?

   Fix: Each boil drives off water and leaves the minerals behind, so repeated topping up concentrates them. Draw fresh water each time; it also avoids the flatness that comes from twice-boiled water.

4. 4. A filter cartridge past its life

   Equipment

   Check: If you filter, how long has the cartridge been in?

   Fix: An exhausted cartridge passes water through unchanged while giving the impression of doing something. Replace on the stated schedule rather than when the water tastes wrong.

Tea types this applies to

• Green tea
• Black tea

Related problems

Sharing a cause category, a tea type or a brewing method with this one.

• My water is not the temperature the kettle says — The kettle is set to 80 °C and the tea behaves as though it were much hotter or much cooler, and the same setting gives different results on different days.
• I bought a water filter for my tea and it changed nothing — A filter jug or tap filter was bought specifically to improve the tea, and the cup tastes the same as it did before — with the same dullness, the same film and the same scale in the kettle.
• My green tea tastes flat and looks dark in this house — A delicate green tea that tasted bright elsewhere comes out dull and heavy here, with a darker, browner liquor than it should have and none of its aroma.
• My tea gets drier and harsher as it cools — The first mouthful is balanced and the last one, several minutes later, grips the tongue and feels rough — from the same cup, with nothing added.
• My iced tea tastes watery once the ice melts — The tea is good for the first mouthful and thin by the bottom of the glass.

Sources