---
title: "Matcha tastes fishy, grassy or like seaweed: is that normal?"
description: "Umami, marine and grassy notes are part of matcha. When notes are typical of the variety or point to age, and what water, amount, sieve and milk change."
url: "https://rinsumila.com/en/blog/matcha-tastes-fishy-grassy-seaweed"
image: "https://rinsumila.com/images/ratgeber/matcha-pulver-frisch-alt-og-f7f1e4af.jpg"
lang: "en-US"
generated: "2026-10-06T04:00:10.878Z"
source: "rinsumila.com, HTML converted to Markdown at origin"
---

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October 3, 2026 · Updated October 5, 2026Published by [RINSUMILA](https://rinsumila.com/en/about)

# Matcha tastes fishy, grassy or like seaweed: is that normal?

Umami, marine and grassy notes are part of matcha. When notes are typical of the variety or point to age, and what water, amount, sieve and milk change.

![Two small ceramic dishes of matcha powder side by side, one bright green and one duller olive green, with a bamboo scoop between them](https://rinsumila.com/images/ratgeber/matcha-pulver-frisch-alt-6ac54e61.jpg)

A sea or seaweed note can be typical of the variety in matcha, and it comes through more strongly in some varieties than in others. Umami describes a savoury, brothy taste; alongside it, matcha can have an aroma that recalls seaweed or the sea. A grassy or spinach-like note can be part of the flavour profile. Try a consistent preparation at about 75 °C; taste alone reveals neither the grind nor the picking time. A musty or rancid smell, moisture and visible mould are warning signs; you do not keep using powder like that.

## What does matcha actually taste like: umami, a sea note, grass

Matcha is ground green tea whose leaves are shaded before harvest. Under shade the leaves form more amino acids and fewer bitter compounds; this contributes to a brothy, round fullness. Umami describes a savoury, brothy taste, the kind you also know from broth or ripe tomatoes. Alongside it, matcha can have an aroma that recalls seaweed or the sea; some people think of nori or call it "fishy", even though there is no fish involved. On top of that come a light natural sweetness, some astringency and, in many varieties, a fresh green note.

Where the seaweed note can come from was examined in an aroma study from 2025, though on matcha from the Chinese province of Shandong, made from the tea cultivar Zhongcha 108 \[1\]. Of eleven odorants that contributed to the aroma, mainly dimethyl sulfide and α-ionone shaped the seaweed-like note; hexanal, benzaldehyde and β-ionone also contributed. Whether this carries over in the same way to Japanese matcha was not examined in the study. It does show, however, that the note goes back to odorants of the tea itself.

Shading influences the flavour profile; how strongly individual notes come through also depends on the variety and on processing. Look for explicitly described flavour notes; "for latte" or "for Koicha" alone does not describe the flavour profile clearly. If you do not like nori, you do not have to give up on matcha: in a latte the sea note can recede; for matcha on its own, ask for a variety with an explicitly described, subtle marine note.

Grass and hay are something different from umami. A green, grassy or spinach-like note can be part of the flavour profile; how astringent it turns out also depends on water temperature and amount. Taste alone reveals neither the grind nor the picking time.

Why do people drink matcha if it tastes so distinctive? Because of exactly that taste, which no other drink has, because of the short preparation, which can become a ritual, and because of its versatility: on its own in the bowl, as a latte, over ice, in baking. And yes, for many people matcha is an acquired taste. The first bowls often taste strange; after a few tries you notice the sweetness behind the umami. If you still do not like it after that, you do not need to justify yourself; that is fine.

## When a note is normal and when it points to age or storage

A sea note can be typical of the variety. Taste alone confirms neither freshness nor usability. The following features help you judge.

**Normal, even if unfamiliar:**

-   Umami and a sea note, up to what many call "fishy", especially on its own and with stronger varieties.
-   A green, grassy freshness, especially in the first seconds.
-   A light astringency that ends in sweetness in the finish.
-   A smell of fresh hay, seaweed or green vegetables when you open the tin.

**A sign of age, oxidation or wrong storage:**

-   The smell is flat, cardboardy or musty, like old cardboard or a damp cellar.
-   The taste is bitter and astringent without any sweetness, or it recalls rancid oil.
-   The colour is olive, yellowish or brownish instead of bright green.
-   The powder clumps from moisture instead of being loose and dust-fine.

After opening, matcha can lose aroma. Air, light, heat and moisture can favour changes; the cause cannot be determined reliably from a single flavour note. After opening, it is best to use up matcha within a few weeks. Store it cool, dark and dry in a tightly closed pack.

Does the same powder taste fishy only on some days? Variations can be related to preparation, storage or your own perception of taste: sometimes the water was hotter, sometimes the amount larger, sometimes the tin stood open longer, sometimes you had coffee or brushed your teeth beforehand. Keep the amount of water, the temperature and the amount of powder the same, and close the pack immediately after each use.

Two things are in any case a reason to throw the powder away: a clearly musty smell and moisture, meaning powder clumped from damp or visible mould. You also do not use such matcha for baking any more. Colour and taste can indicate changes, but on their own they do not allow a reliable assessment of freshness, quality or usability.

Blends can also have a seaweed note. Check the ingredients list and the product description. A sea note alone proves neither a defect nor freshness.

## The influence of water, amount, sieve

**Water.** Temperature is the biggest lever. 70 to 80 °C is usual, never boiling. With water below 80 °C matcha tastes rounder and less astringent; with boiling water the astringency moves to the front, and many people then find the green and sea notes sharper. If you experience "fishy as soon as water is added", first try a consistent preparation at about 75 °C. A thermometer or a kettle with temperature selection replaces guessing; otherwise let boiling water cool briefly.

**Amount.** Our standard serving for matcha on its own is 2 g in 70 ml of water at about 75 °C. More powder in the same amount of water makes the matcha denser, and umami and the sea note grow with it. For the thick preparation, Koicha, about 3 to 4 g in 30 to 40 ml of water is usual, and it tastes correspondingly denser. If you want the note quieter, use a little less powder or a little more water. For a latte, whisk 2 g in 30 ml of water, then add 200 ml of milk or oat drink.

**Sieve.** Unsieved powder forms small lumps that do not fully disperse when whisked. In the mouth they burst open as concentrated bitter, dry grains, and that strengthens the impression of "grassy" or "dusty". Sieve, then whisk with the Chasen in zigzag movements for about 15 to 30 seconds into a fine foam. You can try a small metal whisk; make sure no lumps remain. For fine foam the Chasen is more reliable. An electric milk frother is another option for the latte.

Humidity plays a part too. In a humid climate the powder draws water from the air, clumps faster and loses aroma. What helps then: a small pack, closing it immediately after each use, not storing it next to the stove or sink, and letting the pack come to room temperature before opening if it comes from the fridge, so that no condensation forms on the powder.

The amounts and temperatures in detail are covered in the guide on [amount, ratio and water temperature](https://rinsumila.com/en/blog/matcha-ratio-water-temperature).

## Tricks: milk, sweetness, ice

**Milk.** Yes, milk helps. It softens astringency and masks the marine note; that is why many people find the same matcha mild in a latte when it was too strong on its own. Oat drink brings a light sweetness of its own, cow's milk is creamy and neutral. Hot milk is a special case: some people find that a powder is pleasant in cold milk but tastes fishy in hot milk. Warmth lifts aromas, and very hot milk brings cooked notes of its own. In that case you whisk the matcha with water at about 75 °C and add milk that is warm rather than hot, or switch to the cold version.

**Sweetness.** A small splash of syrup rounds off astringency and umami; sugar and honey dissolve more easily in the warm base. Start with little sweetness and adjust it to your taste. If you do not want to add sweetness, try oat drink, which is slightly sweet by itself.

**Ice.** Cold dampens aromas. In an iced latte umami and the sea note recede, and the freshness stays. To do this, whisk the base warm, put ice in the glass, add cold milk, and pour the base in last. On its own with cold water matcha also tastes softer, but then needs thorough sieving and vigorous whisking.

Milk and sweetness can cover flavour notes, but they do not confirm freshness. If the taste stays unpleasant, check the storage and the product description. With a musty or rancid smell, moisture or mould, you do not keep using the powder. For getting started, a variety for latte is a good fit; if you like the umami, you switch later to a variety for the bowl. Our [RINSUMILA PURE](https://rinsumila.com/en/products/rinsumila-pure) is made for matcha served straight in a bowl, RINSUMILA DAILY for latte and iced latte.

## How to recognise old matcha

Four checks that need no laboratory:

1.  **Colour.** Spread a little powder on white paper. You can compare the colour with earlier packs of the same variety. A change can point to storage conditions; the colour alone proves neither age nor inferior leaves.
2.  **Dry smell.** Smell the powder in the opened pack. Greenish, sweetish, hay-like or seaweed-like smells can be part of the variety profile. A flat or cardboardy smell can point to loss of aroma; a musty or rancid smell is a warning sign. The age cannot be determined reliably from the smell alone.
3.  **Texture.** Fresh powder is dust-fine and loose; damp lumps that cannot be crushed are a bad sign.
4.  **No tasting with warning signs.** Discard powder that is musty, damp, clumped from moisture or visibly mouldy, without tasting it. With a clearly rancid smell you do not keep using it and you contact the seller.

Also look at the pack: the best-before date is printed there, on our products together with the batch number on a sticker. A date far in the future says nothing about how long the pack has been open, though; what matters is how long the pack has been open since you opened it and how you store it. Musty, damp or mouldy: throw it away.

## What you can write to the seller

Taste alone is not a defect. If a variety is too strong in umami or too seaweedy for you, but it arrived fresh, well stored and as described, that is a preference; asking for a milder variety or switching to latte then helps. In distance selling, consumers have a right of withdrawal of 14 days; exceptions apply in the cases set out by law, for example for sealed goods that are not suitable for return for hygiene reasons if the seal has been removed. Details are in the shop's withdrawal information.

It is a matter for the seller, on the other hand, if

-   the powder smells musty or rancid already on opening or is clumped from damp,
-   mould is visible,
-   the pack arrived damaged or leaking,
-   the best-before date had already passed on delivery or
-   the contents do not match the description, for example a sweetened blend instead of pure matcha.

Then the statutory rights in case of defects apply. So that the seller can examine the case, send them:

-   Order number, product and purchase date.
-   Batch number and best-before date from the label.
-   Date of opening and how the powder has been stored since.
-   What exactly stands out: dry smell, taste, colour, texture, in a few words.
-   Photos of the powder on white paper and of the label.

With the batch number and best-before date the seller can identify the batch and check whether other packs are affected; with our products you look up the batch via the QR code on the pack. Good sellers reply with a replacement, a refund or an explanation of why the note is intended for this variety.

## Frequently asked questions

### Is a sea or seaweed note a defect?

Not necessarily. A sea note can be typical of the variety and comes through more clearly in the thick preparation (Koicha) with more powder in less water. Umami, by contrast, describes a savoury, brothy taste. A musty or rancid smell, moisture and visible mould are warning signs.

### Which note comes from shading, which from age or oxidation?

Shading influences the flavour profile; how strongly individual notes come through also depends on the variety and on processing. After opening, matcha can lose aroma; a flat, cardboardy or rancid character and an olive-green colour are indications of that, but the cause cannot be determined reliably from a single note. A grassy or spinach-like note can be part of the flavour profile; taste alone reveals neither the grind nor the picking time.

### What changes with water below 80 degrees?

The matcha tastes rounder and less astringent. With boiling water the astringency moves to the front, and many people then find the green and sea notes sharper. 70 to 80 °C is usual, and our standard serving for matcha on its own is 2 g in 70 ml of water at about 75 °C.

### Does adding milk help?

Yes, milk softens astringency and masks the marine note; in a latte the same matcha tastes much milder. Very hot milk can emphasise the note, though, so whisk the matcha with water at about 75 °C and add warm or cold milk. Milk can cover notes, but it does not confirm freshness.

### When should you make a complaint?

If the powder smells musty or rancid, is clumped from damp or mouldy, the pack arrived damaged, the best-before date had passed on delivery or the contents do not match the description. Send the seller the order number, batch number, best-before date, date of opening, storage and photos. A strong umami note alone is not a defect.

## Sources

1.  Zhang Y, Wu X, Shi Y, Qu F, Qi D, Qian W, Zhang X, Hu J (2025): [Identification of key odorants responsible for the seaweed-like aroma quality of Shandong matcha](https://doi.org/10.1016/j.foodres.2025.115945). Food Research International 204:115945.

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