陶壺釉面之物性分析及對茶湯香氣的影響

Characterization of the Glazed Pottery Pot and Its Impact on Tea Aroma

茶器是茶文化最具表現力的載體之一，目前常見的陶製茶壺分成上釉與不上釉兩類。上釉與否直接影響茶湯的風味。本研究探討白釉壺代號H、牡蠣殼灰釉壺H 20與不上釉的素坯壺N,對照組等三種不同陶壺，比較其表面形貌、顯微結構、晶相組成、表面親水性與壺身熱傳導性等的差異，並分析所沖泡之台灣高山茶湯之揮發性化學組成，藉此探討壺質影響茶湯香氣之原因，闡明不同壺質對茶湯香氣組成及含量的相關性與可能原因。顯微影像顯示N壺表面最粗糙，富含直徑小於數微米的孔洞。H表面最平整緻密，但因燒製時的熱應力，有些許裂紋。H 20壺表面緻密但不平整。水滴接觸角contact angle測量值可推估各表面的親水性。N壺為19.7 o，略低H壺，推估其具有三者中最佳的表面親水性。H 20壺最高，為26.1 o，推估其表面較容易吸附茶湯中的非極性物質。
X rays繞射分析顯示：三壺均為含玻璃相的結晶陶瓷結構，其中H 20結晶相組成較多元，包含鋇、鉀等。茶壺的導熱性實驗結果顯示：白釉壺的保溫性最佳。清香型高山烏龍茶茶湯中的有機揮發物，經過氣相層析質譜儀GC／MS分析，結果顯示整體有機揮發物組成以烷類所佔比率最高，其次為矽氧烷類與有烯、醇與酯類。茶香揮發成分以羅勒烯Ocimene與吲哚Indole為代表。三壺中以H 20沖泡的茶湯，含最多種揮發物，主因在H 20壺表面較高的疏水性，有利於吸附眾多油溶性有機分子。

Teaware is among the most expressive media for conveying tea culture. Common ceramic teapots are either glazed or unglazed, which directly affects the flavor of the tea infusion. In this study, we compared three different types of ceramic teapots, namely white glazed teapots (code H), oyster-shell gray glazed teapots (H-20), and unglazed biscuit teapots (N, control), in terms of their surface morphology, microstructures, crystalline composition, surface hydrophilicity, and thermal conductivity. We also explored the volatile chemical compositions of the infusions that were prepared from Taiwanese high-mountain teas within these teapots in order to elucidate the effects of the quality of the teapots on the composition and content of the tea infusion aroma.
Scanning electron micrographs showed that N had the roughest surface, with holes smaller than a few micrometers in diameter, whereas H had the smoothest and densest surface, with some cracking engendered by the thermal stress of firing. H-20 had a dense but uneven surface. Surface hydrophilicity was inferred from the droplet contact angle, which, at 19.7°, was slightly lower for N than for H, suggesting that it had the best surface hydrophilicity of the three. The droplet contact angle for H-20 was 26.1°, which was the highest among the three, suggesting that the surface of H-20 was more susceptible to adsorbing nonpolar substances in the tea infusion.
X-ray analysis revealed that all three teapots were crystalline ceramics with glassy phases; H-20 exhibited a more diverse composition that included barium and potassium. H had the best thermal conductivity. The organic volatiles in the infusion prepared in the clear-flavored high-mountain oolong tea were analyzed through gas chromatography–mass spectrometry. The results indicated that alkanes accounted for the highest proportion of the overall organic volatiles, followed by siloxanes, alkenes, alcohols, and esters. Ocimene and indole were the most important volatile components in the tea aroma. Among the tea infusions brewed in the three pots, the infusion brewed in H-20 contained the most volatiles; this can primarily be attributed to the high hydrophobicity of the surface of H-20 pots, which is conducive to the adsorption of numerous oil-soluble organic molecules.