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Tea off-flavours - mustiness, over-roasting, age

It is not only wine, beer and coffee that have faults - tea does too. Off-flavours, that is undesirable notes, can spoil even a good leaf, and their causes are specific and recognisable. The most common are mustiness from bad storage, over-roasting from excessive firing and notes of age from loss of freshness. The ability to recognise them is a mark of a mature palate and a key to conscious tea drinking - it lets you tell a faulty leaf from a good one and store it better. Importantly, some of these notes can be a feature of the style, not a fault, depending on the type of tea. Here is a guide to tea off-flavours: where mustiness, over-roasting and age come from, how to recognise them and when they are a fault and when not.

Why know tea faults

Recognising faults is a higher level of appreciating tea. It is not about spoiling your pleasure, but about understanding what you sense and why. A fault is not a matter of taste, but a specific defect with a known cause - usually an error in production or storage. When you learn to name them, you start to understand whether the tea is badly stored, over-roasted or simply old. It is knowledge that makes you a conscious taster, helps you choose better teas and store them properly. It also lets you appreciate when a leaf is clean and fresh. Understanding that a fault is a described defect, not a matter of taste, is the starting point. It is the language of tea quality. It is a tool of conscious drinking. We cover describing flavour more in the tea flavour profile.

Mustiness - enemy number one

The most common tea fault is mustiness. It comes from bad storage: tea is remarkably absorbent - it easily takes up moisture and foreign smells from its surroundings. Kept in damp, in a leaky package or near strongly smelling things, it takes on musty, cellar-like, cardboard notes, and in extreme cases mouldy ones. It is a fault purely from the surroundings, not from the leaf itself. Musty tea loses its clean aroma, and the brew becomes flat and unpleasant. It is the most common reason that good tea tastes bad. Understanding that mustiness comes from moisture and absorbed smells is the key to this fault. It is a signal of bad storage. It is the enemy easiest to avoid with proper keeping.

Over-roasting - too heavy a firing

The second fault is over-roasting. Many teas, especially oolongs and some greens or hojicha, undergo roasting (firing) as part of production - and that is good when done skilfully. But when the roasting is too heavy or careless, the leaf over-roasts, giving burnt, ashy, bitter, charcoal and harsh notes. Such an over-roasted taste drowns out the natural character of the tea, instead of emphasising it. It is a fault of production, not storage. It has to be told apart from deliberate, skilful roasting, which adds depth. Understanding that over-roasting is the result of too heavy a firing lets you recognise it. It is the taste of scorching instead of roasted depth. It is the line between craft and error.

A table: three off-flavours

Let us gather them in one place:

The table shows the three main tea off-flavours, their notes and sources. Each has a different cause: storage, production or time.

Age - lost freshness

The third fault is notes of age. Most teas, especially greens and delicate ones, taste best fresh - with time they lose aroma, liveliness and character. Old, stale tea becomes flat, hay-like, dull, stripped of the brightness it had at the start. It is a natural result of the passage of time and slow oxidation. The more delicate and green the tea, the faster it loses freshness. That is why green teas are drunk young, not kept for years. Understanding that notes of age are a loss of freshness over time lets you recognise and avoid them. It is the taste of tea that has outlived its time. It is a signal that the leaf has sat too long.

When a fault, and when a feature

Here a key subtlety: not every one of these notes is always a fault - much depends on the type of tea. Roasting is deliberate and desirable in heavily roasted oolongs (like rock yan cha) or hojicha - there the roasted note is a feature of the style, not a defect. „Age” is a virtue in teas meant for ageing: pu-erh, dark heicha or some oolongs are deliberately aged, so they gain depth. Even a light earthiness can be typical of pu-erh. A fault begins where the note is out of place in the given type and spoils the tea. That is why assessment requires knowing the type. Understanding that the same note can be a fault or a feature depending on the tea is a mark of a taster’s maturity. It is context over a rigid rule. It is the difference between a defect and a character.

Other off-flavours

Beyond the big three, tea has other faults worth knowing. An unintended smoky note (when a tea that should not be smoked smells of smoke) gives away an error in drying over fire. A sour or vinegary note can indicate improper fermentation or moisture. A woody or stemmy note can be the result of careless picking with too many stems. Sometimes tea absorbs a specific smell - fishy, chemical - from its surroundings. Knowing these notes broadens your tasting vocabulary beyond the three main ones. Understanding that there are more faults makes you a more complete taster. It is a further map of tea defects. It is a step towards mastery in assessing the leaf.

How to avoid and recognise them

How to protect tea from faults and detect them? Above all, store it properly: airtight, dry, away from light, heat and strong smells - this prevents mustiness and slows ageing. Drink green and delicate tea fresh. To detect faults, smell the dry leaf and the brew carefully - many off-flavours give themselves away mainly in the smell. Learn by contrasts: compare fresh tea with old, well-roasted with over-roasted. Note what you sense, to build sensory memory. Understanding how to avoid and recognise faults gives practical control over quality. It is training for the palate. We cover proper keeping more in storing tea.

How long tea stays good

Since age is a fault, how long does tea have before it goes stale? It depends greatly on the type. Green and delicate teas (like Japanese sencha) are the least durable - they are best drunk within a few to a dozen or so months of harvest, while they have a fresh, lively aroma. Oolongs and black teas keep longer, usually a year or two, and heavily roasted oolongs longer still. At the other extreme are teas made for ageing: pu-erh, dark heicha and some oolongs can be aged for years, even decades, gaining in depth. The key is to match your expectations to the type. Understanding that the durability of tea depends on the type helps you drink it in the optimal window. It is a calendar of the leaf’s freshness. It is the difference between tea to drink fresh and tea to age.

The essentials in brief

Let us gather it up. Tea has faults (off-flavours) too, with specific causes. Mustiness (cellar, cardboard, mould notes) comes from bad storage - tea absorbs moisture and foreign smells. Over-roasting (burnt, ash, charcoal) is the result of too heavy a firing in production. Notes of age (hay, flatness) are a loss of freshness over time, especially in delicate green teas. Crucially: some of these notes can be a feature, not a fault - roasting is desirable in roasted oolongs, and „age” a virtue in teas meant for ageing like pu-erh; assessment requires knowing the type. There are more faults (smoke, sourness). Protect tea with airtight, dry storage and drink greens fresh. Now you know the main tea off-flavours.

Note every tea in GustoNote - including the faults you sense and their intensity. In time you will learn to recognise mustiness, over-roasting and age and to tell a fault from a feature of the style yourself.