| Summary: | 博士 === 國立中興大學 === 生物產業機電工程學系所 === 96 === By applying the far-infrared ray (FIR) to roast the partially fermented tea tends to retain its original flavor, reducing the roasting time, save the energy and lower down the tea processing costs, having the effects of upgrading tea production technology.
Roasting with FIR on machine-plucked tea (cv. Chinsin Oolong) under 90-100℃ for 2-4 hours had fine tea soup color, aroma and flavor, with tea appearance retaining original blackish green. FIR roasting with 110℃ and 6 hours resulted mild baked flavor; whereas roasting in 120℃ with 4 hours deteriorated tea quality, with yellow red soup color. The tea quality was the worst if roasting time was over 8 hours because of deep soup color, scorched flavor, bitter taste with sourness. For hand-plucked Chinsin Oolong the quality was the best under the conditions of 110℃ roasting for 6 hours. The worst quality was obtained with roasted temperature over 120℃ with 6 hours.
Tea soup pH decreased with the increase of roasted temperature and time. It is suggested that roasting high quality tea the appropriate temperature is around 90 -100℃ with roasting duration of 2-4 hours. For roasting middle and low grade tea, adjustment of FIR roasting temperature and time is needed to meet the quality requirements.
There were significant differences between effects of electric-thermal baking and FIR baking on tea associated with water content, tea soup pH, reducing sugar, amino acid and L-value. Effects on catechin content changes only restricted to EGCG. Caffeine concentration increased with the increase of baking temperature. This may be due to the increase of caffeine solubility after baking or caffeine separated from the complex of caffeine-tannate after baking. Decreases in phenol, folin, and C, EC, ECG, EGCG of catechin were obtained. Effects of baking temperatures on tea chemicals apparently were greater than that of baking duration.
NIRS was used to screen the reflection spectra of NIR baked tea. The NIRS absorbance of NIR baked tea decreased with increases of baking temperatures, revealing that obvious effects of FIR baking on tea aroma.
This study has also developed a continuous FIR baking machine of tested types, possessing functions of withering, drying and baking. The machine is durable, easy operative, having controls for temperature, time and tea leaf input and also having the function of automatically overturning the tea under baking.
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