Today is Minor Cold, one of the twenty-four solar terms, marking the official start of the mid-winter season. The cold air has accumulated over time, indicating that we are about to enter the extremely cold period of the third nine-day cycle of winter when people can walk on ice. In the southern Jiangnan region of China, there is a saying that “Minor Cold and Major Cold are so cold that everything freezes into ice lumps”.
In the vast North China region, the saying “Minor Cold and Major Cold, water freezes into ice” has always been popular. There is a folk proverb that goes, “Nourish the body during the third nine-day cycle of winter, and you will be free from illness in the coming year.” In Guangzhou, there is a custom of eating glutinous rice on the morning of Minor Cold. And Cantonese cured meats are essential ingredients for cooking glutinous rice. People in Guangzhou will stir-fry Cantonese sausages and cured pork in advance until fragrant, and then cook them together with mushrooms, scallions, corn kernels and glutinous rice. It’s extremely fragrant! The soft and delicious glutinous rice symbolizes “warmth”. Coupled with the high fat content of Cantonese cured meats, eating them on Minor Cold days is quite good for keeping out the cold. In addition, there are also customs such as eating instant-boiled mutton, roasted sweet potatoes, roasted chestnuts, and eating Chinese chard in different places. The diet during Minor Cold mainly focuses on “dispelling cold” for health preservation! Of course, drinking a cup of steaming hot tea is an excellent way to dispel cold during the cold days of winter. So, what kind of tea is more suitable to drink after Minor Cold? The widely spread four-season tea-drinking guide in the tea circle, “Drink flower tea in spring, green tea in summer, oolong tea in autumn and black tea in winter”, guides the vast majority of tea lovers to choose black tea as the first choice in the cold winter. Just from the perspective of the production process, black tea, with “fermentation” as the key production process, is a fully fermented tea, and the fermentation degree is as high as 80 – 90%. Compared with lightly fermented and semi-fermented teas, it retains fewer natural substances in fresh tea leaves. The research team led by Professor Yang Weili of Hunan Agricultural University once picked fresh tea leaves from the same origin, variety, and tenderness level. After making samples according to the production processes of the six major tea categories respectively, they measured the content of the main biochemical components of different tea categories. The results showed that on the premise of exactly the same raw materials, among all the tea categories, the flavonoid content of fully fermented black tea (0.155%) is second only to that of white tea (2.205%), while the content of amino acids, tea polyphenols, caffeine, water extracts, and carbohydrates ranks at the bottom. This is sufficient to prove that black tea with a relatively high fermentation degree indeed causes most of the natural substances in fresh tea leaves to oxidize. Especially the significant reduction in the content of tea polyphenols and caffeine makes black tea less irritating to the human gastrointestinal tract. The irritation of tea to the gastrointestinal tract mainly comes from tea polyphenols, caffeine, etc. The reduction in their content weakens the irritation to the gastric mucosa, but it doesn’t mean there is no irritation at all. Therefore, the saying in the tea circle that “black tea nourishes the stomach” is not very accurate. Instead of saying “nourishing the stomach”, it is more appropriate to say “warming the stomach”. With less irritation to the gastrointestinal tract and the gentle nature brought by the fully fermented process, black tea is indeed one of the excellent beverages for dispelling cold and warming the stomach after Minor Cold.However, the control of time and temperature during the fermentation process can affect the quality of black tea. What are the differences in the drinking experience and content of substances contained in black tea made with different fermentation times and temperatures? Domestic research has been conducted under conditions of fermentation temperature between 22~35 degrees Celsius and a relative humidity of 80~90%.
By setting different fermentation temperatures and times, the sensory quality of Gongfu black tea was evaluated, and the physicochemical components were compared. Under certain humidity conditions and the same 4.5-hour fermentation time, as the fermentation temperature increases, the appearance of Gongfu black tea remains essentially unchanged, while the soup color and leaf base gradually deepen, with the best red brightness achieved at a fermentation temperature of 30 degrees. The aroma transitions from green to floral as the fermentation temperature rises, and the taste evolves from a mellow and refreshing flavor at lower fermentation temperatures to a sweet and floral flavor at higher temperatures. Overall sensory quality scores increase and then decrease with the rise in fermentation temperature, reaching the highest score of 92.45 points when the fermentation temperature is 30 degrees. This indicates that both excessively high and low fermentation temperatures are detrimental to the formation of black tea quality! Low temperatures result in weak enzyme activity and incomplete transformation of substances, leading to undesirable qualities such as green taste, low aroma, light flavor, and dark color. Conversely, high fermentation temperatures cause excessive oxidation of polyphenols in the tea leaves and accelerate the combination of enzyme proteins with oxidized polyphenols to form insoluble complexes, resulting in dark tea soup and decreased quality. Under consistent humidity and fermentation temperature (30 degrees), as the fermentation time increases, the appearance remains largely unchanged, and the soup color of the black tea gradually deepens from dark red to dark red with a rich hue, while the leaf base shifts from a bluish-green to a bright red. The aroma gradually loses its green notes and forms a high, refreshing floral scent after 4.5 hours of fermentation. The taste also transitions from a mellow and refreshing flavor at the shortest fermentation time to a sweet and harmonious flavor with a distinct floral note in the soup. When the fermentation time is extended to 5.5 hours, not only does the soup color become darker, but the floral concentration also decreases, and the tea soup taste becomes lighter. The overall sensory quality is highest for Gongfu black tea fermented for 4. 5 hours, with a score of 92.9 points. The sensory evaluation of black tea with different fermentation times shows that both too short and too long fermentation times weaken the quality of black tea, consistent with the results of sensory evaluations at different fermentation temperatures, both of which are related to the differential content of main physicochemical components. Differences in Substances Contained: Under the same fermentation temperature and different fermentation times, the content of tea polyphenols, theaflavins, and amino acids all decrease with the increase in fermentation time, making the black tea soup gradually more harmonious.The primary substance contributing to the concentration of black tea, theaflavin, exhibits an increasing trend followed by a decrease with the extension of fermentation time, reaching its peak at 4.5 hours (7.85%). Meanwhile, theafuscin gradually increases, causing the tea soup to darken continuously. Under the premise of maintaining consistent fermentation time, theaflavins, thearubigins, and amino acids all decrease with the rise of fermentation temperature; conversely, theafuscin shows an inverse relationship, with longer fermentation times resulting in higher content and darker tea soup.
As the fermentation temperature increases, theaflavins rise from low to high, peaking at 7.96% when the fermentation temperature is 30 degrees Celsius, before decreasing, which is consistent with the results of sensory quality evaluation mentioned above. It is evident that even for fully fermented black tea, the control of fermentation time and temperature has a significant impact on the final quality of the tea, with optimal fermentation time and temperature yielding the best quality. Insufficient fermentation (short time, low temperature) can lead to a green flavor and insufficient taste in black tea; excessive fermentation (long time, high temperature) can also weaken the color, aroma, and taste of black tea, resulting in a poor drinking experience. With this understanding, everyone should now know how to choose black tea for dispelling cold after Xiao Han. Black teas with a strong green odor or heavy fermentation scent are likely to be of lower quality due to poor control of fermentation time and temperature and are not recommended for selection.
