How much is the fermentation degree of black tea? Comprehensive evaluation method of "fermentation" degree of black tea

Recently, Ning Jingming, a professor at Anhui Agricultural University's School of Tea and Food Science and Technology, combined with near-infrared spectroscopy technology with computer vision system, established a simple and objective comprehensive evaluation method of "fermentation" of black teaThe results were published online in LWT-Food Science and TechnologyHow much is the fermentedblack tea?black tea is one of the world's most popular beverages, accounting for about 78% of the global tea tradeBlack tea is processed by the process of withering, kneading, fermentation and drying of fresh leaves of tea, of which fermentation is one of the most critical processes in the processing of black teaUnder certain temperature and humidity conditions, a series of changes occurred in the tea after kneading, which involves chemical changes in the substances contained in the tea, but also physical changes in appearance, insufficient fermentation or excessive fermentation will affect the quality of black teaTherefore, it is very important to correctly judge the fermentation degree of black tea in processingfermentation is the key process of black tea processing, after fermentation, leaf color from green to red, the formation of black tea black leaf red soup quality characteristicsThe essence of black tea fermentation is that the leaf in the kneading action, leaf cell tissue structure is damaged, semi-permeable liquid bubble film damage, permeability increased, so that polyphenols and oxidase full contact, causing polyphenols enzyme-promoting action, and produce a series of oxidation, polymerization, contraction and other reactions, the formation of colored substances, such as jaundice, tea hemin, while producing a special fragrance of substancesthe quality of black tea fermentation and the fermentation process of the environment temperature, humidity, oxygen and length of time and other factorsUsually the room temperature is controlled at about 20 to 25 degrees C, and it is appropriate to keep the fermented leaf temperature at about 30 degrees CThe air humidity is maintained at more than 90%, which is conducive to improving the activity of polyphenol oxidase and the formation and accumulation of luteinIn fermentation needs to consume a lot of oxygen, so to maintain good ventilation during fermentation, pay attention to thermal ventilationThe thickness of the stall leaves affects ventilation and leaf temperature, the stall leaves are too thick, the ventilation is poor, the leaf is too thin, the leaf temperature is not easy to retainThe thickness of the stall leaves is generally 10 to 20 cm, the young leaves and small leaf-type to be thin spread; Be thick when the temperature is low; The length of fermentation time varies greatly due to fermentation conditions, kneading degree, leaf quality, tea varieties and production season, and should be moderate fermentationThe fermentation time of famous work-man's black tea is generally 2 to 3 hoursthe degree of fermentation should master the "prefer light not heavy" principle, the moderate standard is: fermentation leaves grass gas disappeared, with obvious flower and fruit aroma, leaf color redThe color of the fermented leaves varies slightly with the seasons and the fresh leaves, the general spring tea is yellow-red, the summer tea is red-yellow; If the fermentation is insufficient, then the tea aroma is not pure, with green air, after brewing the soup color is not red, taste green, leaf bottom bruisingIf the fermentation is excessive, then the tea aroma is low and stuffy, after brewing the soup color is dark and cloudy, taste plain, the bottom of the leaf red dark douous stripsIf the aroma with the acid indicates that fermentation has been excessivethere are many methods of fermentation of black tea, including natural fermentation, fermentation chamber and fermentation machineNatural fermentation is the most traditional fermentation method by putting kneading leaves into bamboo baskets and covering them with a damp cloth and placing them in a ventilated roomFermentation room is a special independent space set up by the tea processing workshop for the fermentation of black teaFermentation machine fermentation, because it can achieve temperature control and humidity control, in recent years, the development is relatively fast, more widely usedspan style"font-size: 12px;" a simple, objective comprehensive evaluation method of "fermentation" of black tea " style" font-size:12px;"Ningjingming introduced that at present, in production and processing, the degree of fermentation of black tea After the conclusion of the "span style" "font-size:12px", "all rely on artificial experience, producers usually according to the color and smell of the leaves to carry out subjective evaluation, lack of quantitative evaluation criteria, the operator's experience, psychological state, environment and other factors will affect the evaluation results, resulting in product quality is not uniform, can not achieve standardized productionTherefore, the precise and quantitative determination of the fermentation degree of black tea is one of the technical bottlenecks restricting the standardized processing of black teaNingjingming team used near-infrared spectroscopy technology to monitor the changes in the main chemical composition of tea in the fermentation process, using computer vision system to monitor the change of tea appearance colorOn the basis of information fusion, a model of black tea fermentation degree determination is established by combining chemometric methods, which has the characteristics of precision and quantification, and can be judged in 1 minutethe application of this technology, will strongly promote the intelligent and standardized level of tea processing, but also for other agricultural products standardized processing provides a reference related paper information: Source: Li Chen China Science Daily, China Tea Equipment