Tea is extracted with hot water, filtered, stored, blended, sterilized and filled, etc. Especially when the tea water is extracted and sterilized with high temperature, its aroma components are lost or destroyed more seriously. The biggest problem with the quality of these beverages is that they do not have the aroma of freshly brewed tea. Conventional extraction techniques cannot sufficiently infuse and capture the aromatic flavor characteristics of tea, especially the head aroma.

Loss of aroma due to processing

Researchers analyzing the changes in aroma composition of canned green tea beverages after sterilization concluded that: after sterilization, the content of cis-3-hexenol, linalool oxide and nerol tertiary alcohol in tea beverages decreased; the content of geraniol and benzyl alcohol increased; and the content of compounds such as β-phyllophenone, 4-vinylphenol, and indole also increased significantly. This is due to the heating decomposition of the ligands in the tea, resulting in an increase in the above compounds such as enols and benzyl alcohols, which disrupts the balance of the aroma components of green tea and ultimately leads to the production of hot soup flavor.

Another study on the aroma changes during the processing of green tea beverages showed that the aroma components were extracted by SDE method, and the total amount of low-boiling-point aroma components, the total amount of high-boiling-point aroma components, and the total amount of all aroma components were reduced by 47. 44%, 39. 0%, and 40. 86% after extraction compared with that of the reflame green tea treatment, respectively.

The FI index was smaller than that of the refire treatment, and the aroma quality was reduced. The study also showed that the higher the extraction temperature and the longer the extraction time, the greater the loss of aroma component content.

The effect of UHT sterilization on the aroma components of green tea raw materials is also very obvious, after 137 ℃, 4 s thermal sterilization, the total amount of low-boiling-point aroma components increased, while the content of high-boiling-point aroma components decreased, resulting in a decrease in the F I index, which led to a decrease in the quality of the aroma, and the taste of the ripe soup was obvious.

The processing of instant tea and tea concentrate goes through the processes of extraction, coarse filtration, cooling, fine filtration or centrifugation, vacuum concentration, blending, sterilization and spray drying. The traditional processing of instant tea will lose too much tea flavor.

Research and production practice has proved that after hot water extraction of tea, there is almost the same fresh aroma concentration as freshly brewed tea, but in each subsequent process (e.g., extraction, filtration, heat concentration, sterilization and spray drying, etc.), due to the heating, vacuuming, oxygen and pumping, etc., there is a loss of aroma in each process, especially in the vacuum concentration and spray drying process, resulting in the production of instant powder or tea concentrate, aroma The intensity of the freshly brewed tea is almost only 10% to 20%. The most serious loss is characterized by the “fragrance” of the low-boiling point volatile components.

The study of instant green tea in the processing of aroma changes show that the green tea after extraction, concentration and spray drying operations, aroma components, aroma components of the group score and sensory flavor are significantly reduced trend.

Compared with the raw green tea, the raw material had 59 kinds of aroma components, the total amount of aroma components of the extract was lost by 35.63%, and 47 kinds of aroma components were retained; the total amount of aroma components of the concentrated juice was lost by 82.03%, and 35 kinds of aroma components were retained; and the total amount of aroma components after the spray-drying operation was lost by 94.78%, and only 6 kinds of aroma components were retained. The aroma of the finished instant green tea is almost gone, and its green tea aroma flavor characteristics no longer exist.

Aroma improvement technology

1. The use of multiple varieties of green tea combination of new tea beverage aroma
China’s tea producing areas are vast, many varieties, diversified environmental conditions have formed different types of tea aroma. Different varieties of tea, origin, season, cultivation conditions, raw materials, old and young and the same type of tea with different processing techniques have a different impact on the aroma of tea, thus forming a unique tea aroma.

China’s main tea categories are: black tea, green tea, green tea and flower tea, etc., of which green tea is the most common. Green tea is the largest production of a class of tea in China. It is made from fresh leaves through three processes: greening (frying or steaming), kneading and drying.

Some green teas are characterized by a clear and elegant aroma (head fragrance), some by a strong and long-lasting aroma (base fragrance), some by a young fragrance, and some by a nutty aroma. Therefore, the use of different green tea varieties of their respective characteristics, the combination of blending, to create a new type of green tea beverage flavor, which is one of the effective measures to improve the aroma of tea beverages.

2. Using ultrafiltration and reverse osmosis membrane concentration instead of vacuum concentration
Using the characteristics of reverse osmosis membrane, under the condition that there is no phase change in tea, it can achieve the purpose of concentration of tea, and to a certain extent, reduce the loss of tea aroma and improve the aroma quality of instant tea powder . Especially the tea concentrate produced by the combination of UHT and aseptic filling technology, the aroma is better than the aroma of instant tea powder.

3. Adopt freeze-drying process to dry tea powder
First of all, 25% of the tea concentrate juice quick-freezing, quick-freezing temperature of – 25 ℃, quick-freezing time ≤ 2. 5 h, and then in the vacuum degree of 66. 7 ~ 266. 6 Pa conditions, heating, so that the moisture in the material from the solid ice sublimation into steam, so that the material dehydration and drying. Freeze-drying is considered to be an effective measure to reduce the loss of tea aroma.

The aroma components of oolong tea extract, spray-dried powder and freeze-dried powder were analyzed by GC- MS, and the results showed that 46 components could be detected in the spray-dried powder, 52 aroma components in the freeze-dried powder, and 52 aroma components in the extract. After sensory evaluation, the flavor of freeze-dried powder is better than that of spray-dried powder.

4. High-temperature refire treatment
In the tea industry, high-temperature reheating treatment of tea leaves to improve the aroma of tea is considered an effective measure. Through the study of the formation and change of aroma composition in the process of green tea tempering, it is found that green tea after tempering in addition to the formation of pyrroles, pyrazines and furans, but also the formation of 3,7 – dimethyl – 1,5,7 – trioctenol and phenyl acetaldehyde.

Among them, methyl pyrazine, 2,5 – dimethyl pyrazine, 1 – ethyl pyrrole – 2 – aldehyde, 2 – acetyl pyrrole and sugar aldehyde are mainly formed. A small amount of these compounds can significantly improve the aroma of green tea.

5. Add aroma additives
In order to make up for the loss of aroma in the processing of tea beverages, instant tea powder or tea concentrate, using the addition of flavors, fragrances or aroma improvement additives, such as β – cyclized dextrin, to a certain extent, can make up for or mitigate the loss of aroma in the processing of tea beverages.

6. “ARS” aroma improvement technology
“ARS” technology principle is: in order to avoid the loss of tea or tea varieties of special head aroma in the production process, the first in the tea extraction, the use of special aroma extraction device (ARS), from the tea and water composition of the tea pulp in continuous separation and extraction of tea and tea in the aroma compounds. The extracted tea aroma substances are condensed and refrigerated to maintain the best aroma quality. The extracted tea pulp and tea water can be further separated, filtered and concentrated into tea concentrate according to the conventional process.

Then, the extracted tea aroma liquid can be added back using the following methods: rejoin the mix in the tea concentrate juice, and then by UHT and aseptic filling, to produce tea concentrate juice; rejoin the mix in the tea concentrate juice, and then spray drying or freeze-drying, to produce highly aromatic instant tea powder; add in the mixing process of the tea powder, to produce highly aromatic instant tea powder; in the production of tea beverages as a natural flavor In the production of tea drinks, it is added as a natural flavor enhancer to produce high-flavor tea drinks.

The aroma of tea extract is produced by the “ARS” technology through the processing of tea pulp, similar to the aroma of freshly brewed tea. Comparison of the tea extracts obtained by using conventional extraction equipment and the “ARS” technology with a GC analyzer showed that the tea extracts obtained by using the “ARS” technology had a higher content (concentration) of aromatic substances (especially the first aroma).

When the aroma liquid is added back to the tea concentrate, the aroma concentrate, after UHT sterilization and aseptic filling to make tea concentrate, or spray drying to make instant tea, the product shows excellent fresh, fresh or floral aroma characteristics. Especially, the performance of tea concentrate products is especially outstanding, which can maintain 85% to 90% of the aroma characteristics and intensity of tea.