Aroma Compounds: Where Aged Aroma and Pile Taste Come From

Open a new raw cake and you smell the fresh scent of sun-dried tea and floral notes; open a ripe cake and it's a warm, aged aroma, with a bit of pile taste in newly made ripe tea; in raw tea stored for many years, people describe wood, herbal notes, or a camphorwood chest. These descriptions all correspond to volatile compounds in the tea. Tea can contain hundreds of kinds of aroma compounds, all at very low levels, often parts per million or less, yet they define a tea's character.

How Aroma Is Measured

Research on pu'er aroma often uses "headspace solid-phase microextraction" to capture the gases released by the tea, which are then separated and identified by gas chromatography–mass spectrometry. Results are usually given as "relative content," the percentage a compound makes up of all aroma measured. This makes it easy to compare samples, but figures from different labs can't be directly added up or compared.

Raw Tea's Aroma: Floral, Fresh, and Sun-Dried Notes

In new raw pu'er, alcohols take the lead, commonly linalool and its oxides, geraniol, and α-terpineol, bringing floral notes and a fresh sweetness; aldehydes and some alcohols add fresh, grassy tones. Drying maocha in the sun also gives it a distinctive "sun-dried" note, one reason pu'er smells different from oven-dried and pan-fired green teas. See Sun-Dried, Oven-Dried, Pan-Fired.

Ripe Tea's Aged Aroma: Methoxybenzenes

When it comes to ripe pu'er's aroma, research almost always points to the same group of compounds: methoxybenzenes. Those most often named are:

• 1,2,3-trimethoxybenzene
• 1,2,4-trimethoxybenzene
• 1,2-dimethoxybenzene
• 1,2,3,4-tetramethoxybenzene
• 3,4,5-trimethoxytoluene

These are barely detectable in fresh tea leaves and appear in large amounts after wodui, generally thought to be linked to microbes "methylating" phenolic compounds during wodui. Interestingly, some methoxybenzenes smelled on their own come across as stale, even a bit musty; but mixed with woody, floral, and fruity compounds, they become the "aged aroma" people love. Aroma is an ensemble, not decided by any one compound. The wodui process is covered in Wodui: Where Ripe Pu'er Comes From.

How Ripe Tea's Aroma Changes in Storage

A factory lab in Menghai tracked the aroma of the same 7572 ripe cake stored for 1–9 years, with quite nuanced results:

• Decreasing year by year: 1,2,4-trimethoxybenzene, 1,2-dimethoxybenzene, methyl isoeugenol, and terpene alcohols such as linalool and α-terpineol.
• Roughly stable: 1,2,3-trimethoxybenzene, 1,2,3,4-tetramethoxybenzene, and 4-ethylguaiacol.
• Increasing year by year: phytone (a ketone with faint floral, fruity, and hay notes), which made up about 9% of measured aroma after 9 years of storage.

Another study comparing ripe pu'er aged 0, 5, 10, and 15 years found that the "woody aroma" of long-stored ripe tea came mainly from 1,2,3-trimethoxybenzene and cedrol. This fits well with tea drinkers' experience that "after a few years, ripe tea loses its pile taste and its aroma becomes settled and woody." 7572 is covered in 7572: The Benchmark for Ripe Tea, and resting ripe tea in Should Ripe Tea Be Aged?

What Is Pile Taste?

Ripe tea that hasn't been out of the pile long often has a smell like damp straw or stuffy earth, which the tea world calls "pile taste." It's generally thought to be volatiles produced during wodui that haven't yet dissipated, so it slowly fades with storage. In tea drinkers' experience, pile taste decreases noticeably after a few months to a year or two of storage; rinsing an extra time and pouring off quickly with boiling water also lets it dissipate in the first infusion or two. Pile taste is different from storage taste and mold; how to tell them apart is in Storage Taste, Aged Aroma, and Mold.

Raw Tea's Aroma After Aging

In raw tea stored for many years, research sees a shared trend: grassy alcohols (such as 1-hexanol) decrease, compounds with woody, resinous notes such as α-pinene and limonene increase, and methoxybenzenes also rise year by year, becoming one of the markers that distinguish young from aged raw tea. In other words, the aged aroma of old raw tea shares a common "skeleton" with ripe tea's aged aroma, but in raw tea it develops slowly and with different layers.

Where Does the Camphor Note Come From?

"Camphor aroma" (zhangxiang) is a sensory description used by tea drinkers for a cool aroma with woody and herbal qualities; it doesn't mean the tea contains camphor. The tea world has several explanations for where it comes from:

• One holds that it comes from the environment where the tea trees grow, for example camphor trees around the tea garden. This view is widespread but currently lacks chemical support.
• Another explains it chemically: the terpene compounds (such as cedrol and pinenes) that aged tea accumulates during long storage, combined with methoxybenzenes, readily evoke smells like camphorwood or cypress.

The safest understanding is that camphor aroma is a type of aroma brought out by aging, related to material, processing, and storage, and not unique to any one mountain or tree. Descriptions of aroma types are in Smelling Aroma.

Small Tips for Better Aroma

• Use boiling water and pour off quickly so volatile compounds are fully released in the steam.
• Smell the gaiwan lid and the bottom of the fairness pitcher; the cool aroma often reveals more layers than the hot aroma.
• With ripe or aged tea, rinse first to clear surface pile taste or storage taste.

FAQ

What compounds make up pu'er's aroma? Hundreds of volatile compounds. Raw tea is dominated by alcohols such as linalool and geraniol, and ripe tea by methoxybenzenes such as 1,2,3-trimethoxybenzene.

What are the main compounds in ripe tea's aroma? Research consistently points to methoxybenzenes, such as 1,2,3-trimethoxybenzene, 1,2,4-trimethoxybenzene, and 1,2-dimethoxybenzene, which together with woody, floral, and fruity compounds form the aged aroma.

How does aged aroma form? Microbial activity during wodui produces methoxybenzenes; in storage, some compounds decrease year by year while others such as phytone and cedrol increase, and the overall aroma becomes settled and woody.

Does the pile taste of new ripe tea fade? Yes. In tea drinkers' experience it fades noticeably after a few months to a year or two of storage, and rinsing an extra time when brewing also helps.