炒菁前茶菁含水率對綠茶品質之影響

Abstract

茶(Camellia sinensis)可依製程製成多種茶類，其中綠茶的製程在茶菁採摘後，經由炒菁、揉捻和乾燥三個主要步驟所製成，但實際作法會在炒菁前適度萎凋 (攤放)，將茶菁含水率降至適宜程度，才進行炒菁。本研究探討炒菁前萎凋過程含水率對綠茶品質之影響，以每處理炒菁前茶菁含水率，約下降1%作為試驗變級，探討茶菁炒菁前之最佳含水率。試驗材料為坪林2019年秋季及2020年春季，手採之‘青心烏龍’茶菁，與三峽2020年秋季及2021年春季，手採之‘青心柑仔’茶菁。依試驗變級製成綠茶後，進行總多元酚、總游離胺基酸、咖啡因、個別兒茶素、揮發性化合物分析及感官品評。 ‘青心烏龍’之茶菁，於含水率70%-71%時進行炒菁，帶有偏蔬菜香或豆香的香氣；而在含水率約於68%-70%時炒菁，則帶有濃淡不一的輕微花香。總多元酚含量於處理間雖達到顯著差異，但含量並不會有明顯的下降；總游離胺基酸及咖啡因含量，於處理間沒有顯著差異。 ‘青心柑仔’於含水率約71%時炒菁，青草味消失，而綠茶香、海苔香及豆香開始出現。與‘青心烏龍’所製之綠茶相比，茶湯香氣屬於傳統綠茶的海苔香及豆香，較感受不到花香，或許與品種本身特性或採摘成熟度較幼嫩有關。‘青心柑仔’所製之春秋兩季綠茶，於總多元酚、總游離胺基酸及咖啡因含量，處理間皆達顯著差異水準。總多元酚含量於兩個季節中，整體上無一定之趨勢；秋季總游離胺基酸含量，隨著萎凋含水率的下降，有逐漸上升的趨勢，春季則呈現上下的波動；秋季綠茶之咖啡因含量，處理間呈不規則變化，春季則呈先降後升的趨勢。 失水率的計算較直覺且容易，但於不同季節中，失水率雖然相同，萎凋程度卻不同。而將含水率作為指標，萎凋程度不受到茶菁初始含水率影響，因此較為合適。先求得茶菁之乾重百分率，即可帶入含水率公式((炒菁前鮮重-乾重)/炒菁前鮮重)×100%，計算出萎凋當下茶菁的含水率。

Tea (Camellia sinensis) can be made into a lot of teas according to the process. The green tea process goes through three main steps panning, rolling, and drying after the tea was made. However, in the actual practice before panning the tea, withering moderately (spreading) was required to reduce the moisture content of the tea leaves to an appropriate level. This study investigated the effect of water content on the quality of green tea during the withering process before panning the green tea. The moisture content of tea leaves before panning was reduced by about 1% as a test variation, and the optimal moisture content of tea leaves before panning green tea was discussed. The materials were hand-plucked ‘Chin-Shin-Oolong’ tea leaves from Pinglin in the autumm of 2019 and spring of 2020, and hand-plucked ‘Chin-Shin-Ganzai’ tea leaves from Sanxia in the autumn of 2020 and spring of 2021. After the green tea was graded according to the test, the analysis of total polyphenols, total free amino acids, caffeine, catechin isomers, volatile compounds, and sensory evaluation was conducted. The tea leaves of ‘Chin-Shin-Oolong’ were panning when the moisture content was 70%-71%, which had a vegetable or bean aroma; and when the water content was about 68%-70%, the green tea had a floral aroma with varied richness. Although the content of total polyphenols was significantly different between treatments, the content did not decrease significantly; content of total free amino acids and caffeine had no significant difference between treatments. When the moisture content of ‘Chin-Shin-Ganzai’ was reached to about 71%, the grass smell was imperceptible, and the aroma of green tea, seaweed and bean started to appear. Compared with ‘Chin-Shin-Oolong’, tea soup of ‘Chin-Shin-Ganzai’ had a seaweed and bean aroma, which is the feature of traditional green tea, and floral aroma was less noticeable The difference may be related to characteristics of the variety itself or tenderness of picking. The spring and autumn green teas produced by ‘Chin-Shin-Ganzai’ had significant differences in the content of total polyphenols, total free amino acids, and caffeine between treatments. In two seasons, the overall trend of total polyphenol content showed a dynamic change; the content of total free amino acids in autumn showed a gradual upward trend with the decrease of withering moisture content, and in spring it showed a dynamic change; the caffeine content of green tea in autumn varies irregularly between treatments, and in spring, it decreased initially and then increased. Calculation of the water loss rate as the index of withering is an intuitive and simple approach, but the optimal water loss varied in different seasons. However, adopting the moisture content as an index, the degree of withering is not affected by the initial moisture content of tea leaves, so it is more suitable. The recommended index of withering, the moisture content formula, was showed below: ((fresh weight before panning - dry weight)/fresh weight before panning)×100% The dry weight percentage of tea leaves must acquire first after tea leaves are picked, then it can provide a better index to determine the timing to the next panning process. First, obtain the dry weight percentage of tea leaves, and then enter the moisture content formula to calculate the moisture content of tea leaves when withered.