Brew Methods Effect on Coffee Flavor and Aroma A
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BREW METHODS EFFECT ON COFFEE FLAVOR AND AROMA A Thesis by TIANYU YAO Submitted to the Office of Graduate and Professional Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Chair of Committee, Rhonda K. Miller Co-Chair of Committee, Christopher R. Kerth Committee Member, Christine Z. Alvarado Head of Department, Boon P. Chew May 2017 Major Subject: Food Science and Technology Copyright 2017 Copyright Tianyu Yao ABSTRACT Coffee is one of the most popular aromatic hot drinks in the world. Numerous coffee brewing methods have been developed to make a cup of coffee. In industry, coffee flavor and aroma is determined by using a method called cupping, but in order to quantitate flavor and aroma in coffee, descriptive sensory is a better option. This study identified how brew methods influence coffee aroma and flavor. Four different roast level Folgers® commercial coffee (Breakfast blend, Classic roast, 100% Colombia and Black silk) were brewed by four brewing methods (pour over, drip, French press, and cold brew) and were tested using a trained descriptive panel using the World Coffee Research (WCR) coffee lexicon. Twenty-five main aroma attributes and thirty-five main flavor and texture attributes of coffee were used. Cold brew method produced the mildest coffee among the four brew methods while drip produced a much stronger coffee. The sensory aroma and flavor differences between different coffee types were not as great as differences between brew methods. From chemical tests, Brix percentage and TDS (Total Dissolved Solids) differed across coffee types and brew methods. Chemical attributes were closely associated with overall impact, body fullness, bitter basic taste and roasted and burnt flavor aromatics. Volatile compounds (n = 271) were identified. Forty-four volatile aromatic compounds differed across coffee types while thirty-seven volatile aromatic compounds differed across brew methods. Folgers® 100% Colombia coffee showed a difference from the other three coffee types by showing higher (P < 0.05) amount of volatile compounds, especially in 2-butenal, and 1-(2- ii hydroxyphenyl)-ethanone (beany aroma). Cold brewed Folgers® 100% Colombia was high on sweet, overall sweet flavor as well as 2,3-hexanedione. The preparation method is a critical factor affecting coffee flavor and aroma. Coffee from the cold brew method was more fruity, floral and sweet whereas coffee from the drip or French press methods were roasted, burnt, and ashy. iii ACKNOWLEDGEMENTS I would like to thank my committee chair, Dr. Miller, my committee co-chair, Dr. Kerth, and my committee member, Dr. Alvarado, for their support and assistance during completion of this research. I feel so fortunate I had the chance to work at the Sensory Lab. I truly appreciate every opportunity I had during the last three years. I would also like to thank all of the graduate students and student workers, especially to Hannah and Blythe, who helped me a lot with the sensory tests, and also to Ale and Kayley, who helped me run gas chromatography (GC) samples. I have learned so many things from every single one of you. You guys made the lab a great place to be. Thanks also to my friends and colleagues and department faculty and staff for making my time at Texas A&M University a great experience. Finally, I would like to thank my mother, father and grandmother for their support and encouragement. iv CONTRIBUTORS AND FUNDING SOURCES This work was supervised by a thesis committee consisting of advisor Professor Rhonda K. Miller and co-advisor Professor Christopher R. Kerth of the Department of Animal Science, and Professor Christine Z. Alvarado of the Department of Poultry Science. All the work for the thesis was completed by the student, in collaboration with Hannah Laird and Blythe Beavers of the Department of Animal Science. There are no outside funding contributions to acknowledge related to the research and compilation of this document. v TABLE OF CONTENTS Page ABSTRACT ............................................................................................................... ii ACKNOWLEDGEMENTS ....................................................................................... iv CONTRIBUTORS AND FUNDING SOURCES ..................................................... v TABLE OF CONTENTS ........................................................................................... vi LIST OF FIGURES ................................................................................................... viii LIST OF TABLES ..................................................................................................... x CHAPTER I INTRODUCTION .......................................................................... 1 CHAPTER II LITERATURE REVIEW ............................................................... 2 Introduction ......................................................................................................... 2 Coffee Processing ................................................................................................ 5 Coffee Brew Methods .......................................................................................... 7 Coffee Flavor and Aroma ................................................................................... 11 Factors Influencing Coffee Flavor ....................................................................... 14 Growth Regions and Conditions .................................................................... 14 Physiology .................................................................................................... 14 Harvesting ...................................................................................................... 15 Picking ......................................................................................................... 15 Roasting ......................................................................................................... 16 Brewing ........................................................................................................ 16 Gas Chromatography and Mass Spectrometry .................................................... 18 Coffee Terminology ............................................................................................. 19 Research Objectives ............................................................................................. 25 CHAPTER III MATERIALS AND METHODS .................................................... 26 Sample Collection ................................................................................................ 26 Descriptive Aroma and Flavor Sensory Evaluation ............................................. 28 Headspace-SPME-GC/MS ................................................................................... 29 Chemical Analysis ............................................................................................... 30 Statistical Design ................................................................................................. 30 vi Page CHAPTER IV RESULTS AND DISCUSSION ..................................................... 32 Expert, Trained Descriptive Coffee Attributes Analysis ..................................... 32 Coffee Types and Brew Methods Interactions ............................................... 32 Differences Among Coffee Types ................................................................. 40 Differences Among Brew Methods ............................................................... 41 Principal Components Analysis ..................................................................... 45 Chemistry Analysis .............................................................................................. 48 Correlation Between Chemical and Descriptive Sensory Analysis ..................... 51 GC/MS Data Analysis.......................................................................................... 55 Coffee Types and Brew Methods Interactions ............................................... 55 Differences Among Coffee Types ................................................................. 56 Differences Among Brew Methods ............................................................... 57 Correlation Between Volatile Compounds and Descriptive Sensory Analysis ... 77 CHAPTER V CONCLUSION ............................................................................... 90 REFERENCES .......................................................................................................... 92 APPENDIX A BALLOT FOR SENSORY TEST ................................................. 102 vii LIST OF FIGURES Page Figure 2.1 The global coffee consumption since 2011 ....................................... 3 Figure 2.2 Total coffee per capita consumption in the United States from 2011 to 2016 in cups per day ...................................................................... 4 Figure 2.3 Total coffee per capita consumption in the United States, by age group in cups per day ........................................................................ 4 Figure 2.4 Method of preparation among past-day coffee drinker in the United States .................................................................................................. 10 Figure 2.5 Drip coffee maker usage among coffee drinker in United States from 2011 to 2016 .............................................................................. 10 Figure 2.6 Quality grading of classes