The secret of aroma changes of TAETEA 7572 is revealed, telling you why Pu'er tea becomes more fragrant as it ages!

The older the Pu'er tea, the more fragrant it is, which is an important manifestation of the time value of Pu'er tea. The longer the storage time of Pu'er tea, the more pleasant sensory experience it can bring to tea lovers in terms of taste, smell, vision, etc.

So how is the "fragrance" in "the older the tea, the more fragrant it is" formed? The expert team of TAETEA No. 7 Courtyard tested the aroma components of 7572 of different years through rigorous scientific experiments, revealing the "aroma mystery" in the aging process of Pu'er tea.

1. Experimental process

In order to find out how the aroma substances in 7572 change over time, and whether the principle is the same as that of liquor, TAETEA No. 7 Courtyard designed a rigorous experiment to explore the mystery.

Experimental samples: 1- to 9-year-old TAETEA 7572 ripe Pu'er tea was selected from Menghai Warehouse (the storage location and storage environment were not changed after production) to ensure the continuity of sample composition changes.

Experimental instruments and methods: Aroma extraction and analysis will use "Headspace Solid Phase Microextraction-GC-MSD Analysis (HS-SPME-GC-MSD)". In a closed glass container, 7572 tea leaves are soaked in a certain proportion of boiling water. After continuous heating, the aroma substances are adsorbed by the probe, and then the aroma components are analyzed in the analysis equipment. The GC-MS uses a 7890A-5975C GC-MS (Agilent, USA).

Evaluation method: The aroma evaluation refers to the tea evaluation standards. A 6-member evaluation team (composed of evaluation experts from the Menghai Tea Factory Technical Center) conducts a tea soup evaluation on the tea samples. 5.0g of tea sample is taken with a tea-to-water ratio of 1:50. The samples are placed in corresponding tea evaluation cups, filled with boiling water, covered and timed. After filtering the tea soup, the tea leaves are evaluated by hot and cold sniffing.

2. Experimental Results and Analysis

The instrument generates a full scan chromatogram for each sample. Figure 1 is the spectrum of the 1-year-old 7572 sample.

Figure 1 Full scan chromatogram of 7572 aroma components

Aroma components of 9 kinds of Pu'er ripe tea 7572 with different aging years were analyzed respectively. Since there are many components in the aroma analysis of Pu'er ripe tea, many aroma components are trace amounts (the content is very small but can be detected in each tea leaf). Considering the convenience of analysis, only the data of 22 aroma components with a percentage content greater than 0.5% were retained. Table 1 is a summary of the aroma percentage content data of 7572 tea aged from 1 to 9 years.

（1） Fragrance characteristics and changing trends of each aroma component

1. Methoxybenzenes

Methoxybenzene compounds are the largest type of aromatic substances in Pu'er ripe tea, and are also the contributors to the "aged aroma" characteristics of aged Pu'er ripe tea. The aroma components detected in TAETEA 7572 include 1,2,3-trimethoxybenzene, 1,2,4-trimethoxybenzene, 1,2-dimethoxybenzene, isoeugenol methyl ether, etc. Table 2 describes the aroma characteristics of these four aroma components.

Among them, the content of 1,2,3-trimethoxybenzene is relatively stable. Although the content fluctuates with the year, there is no obvious increase or decrease trend; while the contents of the three aroma components 1,2,4-trimethoxybenzene, 1,2-dimethoxybenzene and isoeugenol methyl ether decrease, as shown in Figure 2.

Figure 2 Change trend of methoxybenzene aroma substances

2. Terpenes and their derivative compounds

Terpenes and their derivative compounds are important contributors to the diversity of tea aroma, giving Pu'er ripe tea pleasant aromas such as woody, medicinal, sweet, and floral aromas. The main aroma components in TAETEA 7572 are linalool, nerolidol, ionones, guaiacol, pinolein, phyton, and dihydroactin. Table 3 describes the aroma characteristics of these 16 main aroma components.

Among them, those whose contents are stable and do not change with the aging year include nerolidol, 2-nerol, guaiacol, ionone, etc.; the contents of linalool, myrcene and α-terpineol increase with the aging year. Reduction (using spss statistical analysis software, a t test was conducted on the coefficients of the linear regression independent variables between the percentage content and the year. P<0.05, the coefficient is significantly negative, which means that these four substances have a significant decreasing trend); while the plant The contents of ketones and dihydrokiwilactones increased significantly over time, as shown in Figure 3.

Figure 3 Change trend of terpene aroma substances

3. Long-chain organic acids (LCFAs)

Long-chain organic acids can only be detected in aged wine, tea and vinegar, but because of their large molecular weight and lack of obvious aroma characteristics, they have been ignored by aroma researchers. In 2023, Jiangnan University published a paper in Food Chemistry (IF: 8.8), which studied the effects of long-chain organic acids on the sensory properties of aged wine. The paper concluded that "Long-chain organic acids (LCFAs) inhibit the volatilization of most volatile compounds in liquor to a certain extent, promote the volatilization of a few irritating compounds such as ethyl butyrate, reduce the olfactory irritation of liquor, and increase the mellowness of the liquor. In the early study of the change law of liquor during aging, it was also found that as the aging time of the liquor increased, the content of long-chain organic acids (esters) in it also increased, which is also one of the important reasons for the mellow taste of aged wine."

Combined with the changes of long-chain organic acids in the aging process of 7572, it can be boldly speculated that although this type of substance has no obvious aroma characteristics, it makes an important contribution to the coordination, mellowness and palatability of the aroma sensory properties of aged Pu'er tea. The long-chain organic acid aroma substances in TAETEA 7572 mainly include linoleic acid and palmitic acid. Table 4 describes the aroma characteristics of these two aroma components. Both components show a significant growth trend, as shown in Figure 4.

Figure 4. Change trend of long-chain organic acid aroma substances

（2） Trends in the 7572 Aroma Sensory Evaluation

Referring to the tea evaluation standards, 7572 ripe teas of 9 different aging years were evaluated for aroma sensory evaluation, and the results are shown in Table 5. In the early stage of storage, the aroma sensory evaluation of Pu'er ripe tea is relatively complex, with both cold and hot smells accompanied by obvious pile and wood aromas; after 3 years of storage, the aged aroma and sugar aroma began to appear and became more obvious, and the pile and wood aromas disappeared; the aroma of ripe tea aged for more than 7 years is mainly dominated by aged aroma.

（3）Conclusion

By evaluating the aroma of tea leaves of different years and combining the changing trends of aroma components, we can infer the impact of changes in certain combinations of aroma components on the aroma sensory perception. It is not difficult to find that as the years increase, the aged aroma becomes increasingly obvious until it becomes the dominant aroma.

7572The changes in aroma sensory perception combined with the changes in aroma components can lead to the following conclusions:

1
7572 has a richer aroma profile in the early stage, which is related to the diversity of aroma components. Whether it is methoxybenzenes or terpenes and their derivatives, the types are the most numerous at this stage;

2
After 7572 has been stored for 3 years, most of the linalool compounds with low boiling points and prominent aromas have volatilized in large quantities, and the components with a "sugar aroma" compound aroma have begun to increase. At the same time, the content of 1,2,3-trimethoxybenzene with a "aged aroma" main aroma has stabilized, forming a "aged aroma-sugar aroma" aroma during the aging period of 3-6 years;

3
After being stored for more than 7 years, the aroma of 7572 becomes more restrained, and the proportion of the main aroma components tends to be stable (the content of methoxybenzene and terpenoid derivatives is stable). At the same time, under the harmonization of long-chain organic acids, the aroma characteristics of "aging and lasting" are formed.

Finally, the aroma change mechanism of 7572 during the aging process was compared with that of white wine to verify whether the aroma change mechanism has commonality, see Table 7 for details.

By comparing with the aroma change mechanism of liquor, it is found that:

① The volatile components with low boiling point, complex and prominent aroma will gradually evaporate/convert and decrease with the increase of storage time;

② Aged tea and aged wine both form high-content and stable aroma components, such as strong-flavor liquor has a stable and high content of ethyl hexanoate, and 7572 aged tea contains a stable and high content of 1,2,3-trimethoxybenzene;

③ Long-chain organic acids appear in aged tea and aged wine, and the content is high, such as linoleic acid and palmitic acid in 7572 aged tea and aged wine.

This article uses 7572 aged from 1 to 9 years as the research object, and through aroma component analysis combined with sensory evaluation, preliminarily reveals the aroma change pattern of 7572 during the aging process. In the future, TAETEA No. 7 Courtyard will continue to carry out more research on the "aging and better fragrance" of Pu'er tea, so stay tuned.

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