Study on the effect of different roasting processes on the sensory and physicochemical properties of coffee

• Main Authors: Hsu Yuh Sun, 許譽薰
• Other Authors: Yi Long LEE
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/985sgq

碩士 === 國立嘉義大學 === 食品科學系研究所 === 105 === Robusta is a major coffee variety for instant and canned coffee. Although Robusta coffee beans are inexpensive, their products are more bitter, contain higher caffeine, and have other inferior qualities compared with the ones from Arabica beans. Therefore, a better roasting procedure is considered necessary to improve the flavor of Robusta coffee. In this study, raw Robusta coffee beans from Indonesia were roasted in nine different roasting conditions produced by three roasting methods: hot air, semi-hot air, and fire-direct contact, and three roasting degrees: medium roast, high roast, and full city roast. Physicochemical properties analysis and sensory evaluation were conducted to compare the effects of the different roasting conditions. Results showed that the moisture contents of raw coffee beans decreased along with the increase in the roasting degrees. Highest moisture content (2.7%) was found in medium roast-hot air group. Highest caffeine content (110.8 ppm) was detected in full city roast group treated by semi-hot air. As the roasting degree increased, the caffeine content increased in hot air and semi-hot air groups, but decreased progressively in direct contact group. Coffee beans roasted in full city roast-direct contact group gave the highest pH value (6.1), while coffee beans roasted in medium roast-hot air group gave the highest titratable acidity (0.07%). Highest soluble solids (1.54%) were observed in full city roast-direct contact group. Higher time-temperature treatment resulted in lower titratable acidity and higher pH value and soluble solids in all three roasting methods. The color (L value) of the coffee beans were between 35 and 85, highest in medium roast-hot air group. As the roasting temperature increased, coffee beans changed color from green-yellow to brown-black, their acidity decreased, and their aroma became stronger. The main compounds contributed to the aroma were of floral furan class, which was found highest in full city roast-hot air group. Pyrazines were identified mostly in medium roast-hot air group, which consequently resulting in spicy and grassy aroma. Pyridines were found highest in full city roast-direct contact group, producing tobacco, nutty, and biscuit-like aroma. From the sensory evaluation, full city roast-direct contact group gave highest scores in overall likeness and sweetness and lowest score in acidity. Its overall score was even higher than that of commercial sample. The scores for acidity were highest in medium roast-hot air and medium roast-semi-hot air groups. Longer treatment resulted in lower acidity and higher heaviness. Key words: coffee, roasting degrees, roasting methods, sensory evaluation, physicochemical properties