How Scenting Works: Temperature, Timing and the Flower

Scenting works because dry tea leaf adsorbs volatile compounds from fresh flowers, and it depends on three conditions: the leaf must be very dry, the flower must be at the moment of opening, and the pile must be held warm and humid for twelve to fourteen hours. Get any of the three wrong and the leaf takes up little or nothing. The process is called xunzhi and it is closer to a controlled physical adsorption than to a recipe.

The whole method follows from the biology of the flower. Jasmine opens in the evening and releases most of its volatiles in the first hours after opening, which is why the work is done at night and why the timing cannot be moved to suit a factory schedule.

Condition one: a very dry leaf

The base tea is dried to four to five percent moisture, lower than a tea meant for drinking. Water occupies the adsorption sites on the leaf surface, and a damp leaf will not take up aroma.

That is why scented teas are built on baked green tea, which dries evenly and is cheap, rather than on a delicate leaf that would crumble under repeated drying.

The leaf is also sieved to remove dust and stems, because dust adsorbs aroma and then falls to the bottom of the tin where it does nothing for the cup.

Condition two: the flower at the right moment

Jasmine is picked as a closed bud in the afternoon and held cool until evening. The buds are then spread in a warm room and they open over a few hours, releasing their volatiles.

A flower that has opened and faded has already given its aroma to the air. A flower that has not opened will not give it at all. The window is a few hours, and the whole batch has to be worked inside it.

Some producers use a small proportion of already-open flowers to trigger the rest, a practice that spreads the release over a slightly longer period.

Condition three: the pile

Leaf and flowers are layered, usually alternating thin beds of each, and the whole is heaped and covered. The pile warms to 30 to 35 Celsius through the respiration of the flowers.

The warmth helps the volatiles move and keeps the flowers opening, and the moisture from the flowers keeps the leaf surface receptive. Too cool and the transfer stalls; too hot and the leaf sweats and the aroma turns sour.

The pile is turned once or twice during the night to even out temperature and to prevent the center from overheating. In the morning the spent flowers are sieved out and the leaf is dried back down before the next cycle.

• Scenting is adsorption of volatiles onto dry leaf.
• The leaf must be at 4 to 5 percent moisture.
• Jasmine opens after dark and must be worked that night.
• The pile is held at 30 to 35 Celsius for 12 to 14 hours.
• Spent flowers are removed and the leaf is redried each cycle.
• Every condition has a narrow window.

What goes wrong

The most common fault is a damp base. A leaf at seven or eight percent moisture takes up half the aroma and the tea tastes flat despite a full flower ration.

The second is a stale flower. Flowers held too long before use, or picked in the heat of the day, have already released their volatiles and the tea comes out weak.

The third is an overheated pile. A pile that goes above 40 Celsius sweats, the leaf darkens and the aroma acquires a cooked, sour edge that cannot be removed.

A buyer tasting a faulty jasmine tea will find it either faint or sour, and neither can be corrected later. This is why the process is judged by hand and why good scented tea is expensive.

Why the method has not been mechanised

The three conditions are all judgements rather than settings. A producer decides when the flowers are ready by looking at them and smelling them, decides when the pile is warm enough by hand, and decides when the cycle is finished by the aroma.

Machines can control temperature and humidity, and modern scenting rooms do. What they cannot do is decide when a particular batch of flowers has opened enough, because that varies by the day and by the garden.

So the process is semi-mechanised: the room is controlled, the judgement remains human. That is why good scented tea is still expensive and why the quality varies between producers using the same equipment.

The flower supply problem

Jasmine for scenting is grown as an agricultural crop, picked as buds in the afternoon and delivered to the scenting room the same evening. The distance between the garden and the room is therefore a constraint on where scenting can happen.

As Fuzhou expanded, its jasmine gardens were built over, and the city’s scenting industry now relies on flowers trucked in from Guangxi and elsewhere. The tea is still made in Fuzhou and the flowers are not from there.

That is worth knowing because it complicates the meaning of origin on a jasmine tin. The place of scenting and the place of flowering can be hundreds of kilometres apart, and the label usually names the former.

A drinker should therefore treat a Fuzhou claim as a statement about technique rather than about agriculture, which is a reasonable reading and a different one from the marketing.

The white orchid addition is worth a note in the context of the process. Adding a small proportion of orchid to the layering is a traditional technique for giving the jasmine a rounder body, and it is done during the same overnight cycle rather than as a separate step.

The amount is small, usually a few percent of the flower weight, and its effect is on the texture of the aroma rather than its identity. A drinker who notices a creamy undertone in a jasmine tea has probably found it.

That technique is one reason the process resists mechanisation: it is an adjustment made by a producer who knows how the current batch of jasmine is behaving, and no specification captures it.

The scale of the operation is worth a number. A commercial scenting room can handle several tonnes of leaf in a season, and each tonne requires between forty and a hundred kilograms of fresh flowers per cycle, multiplied by the number of cycles.

That is why jasmine is grown as a field crop in Guangxi on a scale that would be unrecognisable to a gardener who knows the plant as a trellis vine. The flower is an industrial input, not a garnish.

It also explains why the price of jasmine tea tracks the jasmine harvest. A poor flowering season raises the cost of every cycle and the tea follows.

• A scenting room handles tonnes of leaf per season.
• Each tonne needs 40 to 100 kg of flowers per cycle.
• Jasmine is grown as a field crop, not a garden vine.
• Tea prices track the jasmine harvest.
• A poor flowering season raises every cycle’s cost.
• The scale is why the technique survives commercially.

Why the base is sieved and sorted first

Before scenting, the base leaf is sieved to remove dust, broken pieces and stems. Dust adsorbs aroma eagerly and then falls to the bottom of the tin, where it contributes nothing to the cup and makes the tea look dirty.

Sorting also evens the leaf size, which matters because the pile must be uniform for the aroma to transfer evenly. A pile with mixed sizes has hot spots and cool spots.

Those steps are invisible in the finished product and they are where a large part of the labour sits. A cheap scented tea is often one that skipped them.

A drinker can see the result: an even leaf with no dust at the bottom of the tin indicates care, and a dusty tin with broken pieces indicates the opposite.

• The base is sieved before scenting to remove dust.
• Dust adsorbs aroma and then sinks, contributing nothing.
• Sorting evens leaf size so the pile transfers uniformly.
• Mixed sizes create hot and cool spots in the pile.
• These steps are invisible in the finished tea.
• Dust at the bottom of a tin indicates skipped work.

Frequently asked questions