커피원두의 분쇄입도에 따른 에스프레소의 품질특성 = (The) quality characteristics of the espresso according to the grinding grades

다국어 초록 (Multilingual Abstract)

Grinding is an indispensible step in the preparation of espresso coffee. The purpose of this study is to provide the basic materials concerning the quality evaluation of the espresso according to the grinding grades ('coarse', 'fine', 'very fine') of the coffee beans by evaluating their mechanical and sensory characteristics.
Specifically, The mechanical characteristics according to the grinding grades of the coffee beans were tested by foam index, persistence of foam, total solids, concentration, extraction yield, viscosity, pH, total soluble solid content, and density. With regard to the sensory characteristics, QDA and acceptance test were carried out through the trained panels.
In conclusion, the optimal grinding grade accepted most favorably by the panels was 'fine'.

1. Foam index
Foam index showed significant (p<0.001) differences among the three categories of the samples. 'Fine' demonstrated the highest value of foam index, which was 19.99 %. And the value of 'very fine' was 16.63 %. That of 'coarse' was 6.25 %.

2. Persistence of foam
Persistence of foam showed significant (p<0.001) differences among the three categories of the samples. 'Very fine' demonstrated the longest value of persistence of foam, which was 61 minutes. And the value of 'fine' was 44 minutes. That of 'coarse' was 5.67 minutes. In other words, The smaller the grinding size of particles was, the longer the persistence of foam was.

3. Total solids, Concentration and Extraction yield
What contained the most amount of total solids contents according to the grinding grades was 'very fine' (43.70 mg/mL). 'Fine' contained 41.27 mg/mL and 'coarse', 31.50 mg/mL. Total solids contents to the grinding grades also showed significant (p<0.001) differences among samples.
Percentage of concentration of 'very fine' was 4.37 %, 'fine', 4.12 % ,and 'coarse', 3.15 %. Percentage of extraction yield of 'very fine' was 20.39 %, 'fine', 19.26 %, and 'coarse', 17.83 %. Both of the two results showed significant (p<0.001) differences among samples.

4. Viscosity
Viscosity of very fine was 4.46 mN/m2s, fine 4.5 mN/m2s and coarse 4.02 mN/m2s. In other words, The bigger particle size was, the more the viscosity decreased significantly. (p<0.001).


5. pH
pH demonstrated the highest value (5.46) in 'very fine'. In the case of 'fine', the value of pH was 5.44, in the case of coarse was 5.37. Therefore, The finer the size of particles was, the higher pH value was, at the p=0.001 value.

6. Total soluble solid content
At the p=0.001 value, The value of total soluble contents to the grinding grades was the highest in 'fine'(0.54 ○brix). Meanwhile, 0.51 ○brix was presented in 'very fine'and 0.41 ○brix, in coarse.

7. Density
Density had the highest value (1.019 g/mL) when grinding grades was the 'very fine'. In the case of 'fine', the value of density was 1.017 g/mL. While in the coarse it was 1.008 g/mL. All of these had significant differences at the p<0.05 level.

8. Sensory evaluation
Color intensity of crema in the visual field was perceived as the strongest in 'very fine'. Its value of the intensity was 9.22 at the p=0.001 level. Meanwhile, 'fine' had 8.58, and 'coarse' had 3.62.
Also, consistency of persistent of crema in the visual field as the longest in 'fine'. Its value of the intensity was 8.75. And 'very fine' had 8.75, 'coarse' had 2.65 at the p=0.05 level.
The result of percentage of judges that perceived each shape of crema characteristics as tiger skin, white spot, hole in the middle, or big bubbles to the grinding grades was as below. The presence of a foam with a "hole in the middle" is the main visual characteristics in 'coarse'. As expected, all of the judges perceived "hole in the middle" in crema. And the presence of a foam with a "tiger-skin" effect is one of the main visual characteristics of 'fine'. As expected, all of the judges perceived "tiger-skin" effect in crema. Meanwhile, the presence of a foam with the "white spot" is the main visual characteristics in 'very fine'. As expected, all of the judges perceived the white spot in crema.
Intensity of aroma was perceived as the strongest in 'coarse'. Its value of the intensity was 7.12. Meanwhile, 'fine' had 6.60, and 'very fine' had 6.45 but there were no significant differences.
Intensity of flavor was perceived as to the strongest in 'fine'. Its value of the intensity was 7.55. And 'coarse' had 6.69, and 'very fine' had 5.13 but these differences were not significant.
The result of percentage of judges that perceived each flavor characteristics to the grinding grades was as below. In the case of 'coarse', 100 percent of trained penals perceived tangy notes. Also, 70 percent of trained panels felt flowery, 30 percent of them felt chocolaty and 20 percent of them felt fruity notes in espresso coffee prepared. In the case of fine, all of the trained panel perceived the flavor of syrupy, 70 percent of them felt chocolaty, 50 percent of them felt dirty, and 30 percent of them felt flowers, fruity and tangy notes. Finally, in the case of very fine, the trained panel perceived the flavor of dirty (90%), earthy (80 %), chocolaty (70 %), syrupy (10 %), and flowers (10 %) notes.
Intensity of acidity in the taste field was perceived as the strongest in 'coarse'. Its value of the intensity was 10.80. Meanwhile, 'very fine' had 7.78, and 'fine' had 7.45 at the p=0.05 level. Intensity of sweetness was perceived as the strongest in 'fine'. Its value of the intensity was 5.87. And 'very fine' had 5.48, 'coarse' had 4.25 but these differences were not significant. Intensity of bitterness was perceived as strongest in 'very fine'. Its value of the intensity was 9.20. Meanwhile, 'fine' had 7.14, and 'coarse' had 6.74 but there were no significant differences. Intensity of aftertaste was perceived as the strongest in 'very fine' Its value of the intensity was 8.22. Meanwhile 'fine' had 7.76, and 'coarse' had 6.93 but these differences were no significant.
Intensity of body in the mouthfeel field was perceived as the strongest in 'very fine'. Its value of the intensity was 6.53. Meanwhile, 'fine' had 5.83, and 'coarse' had 5.73 but there were no significant differences. Intensity of astringency was perceived as the strongest in 'very fine'. Its value of the intensity was 8.73. Meanwhile, 'fine' had 5.98, and coarse had 5.00 at the p=0.05 level.
The highest acceptance of color of crema of espresso to grinding grades of the coffee beans was 'fine' Its value of the acceptance was 10.79 at the p=0.05 level. Meanwhile, 'very fine' had 7.98 and 'coarse' had 6.81.
The highest acceptance of aroma of espresso was 'fine' Its value of the acceptance was 9.72. Meanwhile, 'coarse' had 8.43 and 'very fine' had 5.84 but there were no significant differences.
Acceptance of flavor was the highest in 'fine'(8.78). In the case of 'coarse', the value of the acceptance was 7.72, and in the case of 'very fine', it was 5.68. But there were no significant differences.
Acceptance of taste balance was the highest in 'fine'(9.46). In the case of 'coarse', the value of the acceptance was 7.43, and in the case of 'very fine', it was 5.90. But there were no significant differences.
Finally, acceptance of overall was the highest in 'fine'(9.85), In the case of 'coarse', the value of the acceptance was 8.14, and in the case of 'very fine', it was 6.10. But these differences were no significant.




9. Correlation analysis
Foam index in mechanical characteristics was correlated with both total soluble solid contents in mechanical characteristics and sweetness (p<0.01) in sensory characteristics.
Consistency of persistent of crema in mechanical characteristics was correlated with both viscosity in mechanical characteristics and after-taste in sensory characteristics (p<0.05), but showed the reverse correlation with the intensity of aroma (p<0.05).
Total solids showed correlation with concentration (p<0.01), viscosity (p<0.05), pH (p<0.05), but showed the reverse correlation with the intensity of aroma (p<0.05).
Density showed correlation with persistent of crema (p<0.01), but showed the reverse correlation with the intensity of acidity (p<0.05).
In conclusion, according to the grinding grades, it was identified that there were differences in the mechanical and sensory characteristics. Furthermore, when the size of particles was 'fine', it brought to the most positive result in the overall acceptance.

목차 (Table of Contents)

• < 목 차 >
• I. 서론 1
• 1. 연구배경 1
• 2. 연구목적 5
• II. 이론적 배경 6
• 1. 에스프레소 6
• 1) 에스프레소의 정의 및 구성 6
• 2) 에스프레소의 성분 7
• 3) 에스프레소에 영향을 미치는 요인과 추출조건 13
• 2. 에스프레소의 품질특성 18
• 1) 물리화학적 특성 18
• 2) 관능적 특성 28
• 3. 원두의 분쇄입도 35
• 1) 그라인딩의 목적 35
• 2) 추출 기구에 따른 커피입자의 크기 36
• 3) 그라인더의 종류 및 구조 36
• 4) 커피입도를 측정하는 방법 37
• III. 실험 재료 및 방법 39
• 1. 실험재료 39
• 2. 실험방법 39
• 1) 입자의 크기 선정 39
• 2) 분쇄 크기 분포도 측정 42
• 3) 에스프레소 추출 45
• 3. 이화학적 검사 47
• 1) 크레마 양 47
• 2) 크레마 지속성 47
• 3) 고형분 함량 47
• 4) 추출농도 48
• 5) 추출수율 48
• 6) pH 48
• 7) 점도 48
• 8) 당도 50
• 9) 밀도 50
• 4. 관능검사 51
• 1) 정량적 묘사분석 51
• (1) 패널 훈련 및 선정 51
• (2) 묘사어 선정 51
• (3) 평가방법 및 척도 54
• (4) 시료준비 및 제시 55
• 5. 통계처리 55
• IV. 실험결과 및 고찰 56
• 1. 이화학적 특성 56
• 1) 원두의 분쇄 입도에 따른 크레마 양 56
• 2) 원두의 분쇄 입도에 따른 크레마 지속성 57
• 3) 원두의 분쇄 입도에 따른 고형분 함량 57
• 4) 원두의 분쇄 입도에 따른 추출농도 58
• 5) 원두의 분쇄 입도에 따른 추출수율 58
• 6) 원두의 분쇄 입도에 따른 점도 59
• 7) 원두의 분쇄 입도에 따른 pH 59
• 8) 원두의 분쇄 입도에 따른 당도 60
• 9) 원두의 분쇄 입도에 따른 밀도 60
• 2. 관능적 특성 62
• 1) 정량적 묘사분석 62
• 2) 기호도 검사 71
• 3. 기계적 검사와 정량적묘사분석 결과간의 상관분석 74
• V. 결론 및 시사점 78
• 1. 연구결과 요약 78
• 2. 연구의 시사점 84
• 참고문헌 85
• Abstract 97
• Appendix 103