Allowing for the Movement of the Coffee Beans

168 Pages·2017·11.13 MB·English

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thesis.
The Art of Coffee Roasting
Investigations into Sensor Development for the Application of Controlling
Coffee Roasting
A thesis
submitted in fulfilment
of the requirements for the degree
of
Doctorate of Philosophy in Electronic Engineering
at
The University of Waikato
by
Cameron Kelly

2018

Abstract
In this thesis, I investigate novel methods of sensing change in roasting coffee.
Coffee roasting is a vital step in coffee’s supply chain. It is the process that takes
green coffee and transforms it via a series of many chemical and physical reactions
to produce the flavours for which coffee is recognised. As of today, correctly
roasted coffee has been an art. My work applies different methods of sensing to
track various changes in coffee as it roasts with the end goal of automating the art.
The goal was to find an event or measurable phenomenon that could be used to
detect when the roasting coffee has reached an ideal point, beyond which the beans
would start to taste burnt. My investigations looked at various sensing methods. I
expanded on three different areas of test: bean temperature, online moisture
measurement using microwave resonance, and surface chemistry using Raman
spectrometry. Using these different methods, I was able to produce novel and
interesting measurements.
Each of the measurement methods performed satisfactorily and produced novel
results. These results however did not produce the desired measurable event or
independent characteristics. This meant that they were not able to individually solve
the problem. However, their uniqueness and application flexibility would allow
them to be used as elements in future roasting sensor systems.

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Contents
Abstract .................................................................................................................... i
Contents ................................................................................................................. iii
List of Figures ....................................................................................................... vii
1 Thesis Summary ............................................................................................... 1
Scope ........................................................................................................ 2
Chapter Breakdown .................................................................................. 3
Thesis Contribution .................................................................................. 4
1.3.1 Coffee Thermal Analysis .................................................................. 4
1.3.2 Microwave Aquametry...................................................................... 5
1.3.3 Raman Spectrometry ......................................................................... 5
1.3.4 Published Works ............................................................................... 6
2 The Coffee Problem ......................................................................................... 7
Origin of Coffee by Historical Reference ................................................ 7
Coffee Process Chain ............................................................................... 8
2.2.1 Growing Coffee: Geography and Biology ........................................ 8
2.2.2 Cherry Processing, Bean Drying, Parchment Hulling, and Grading 9
2.2.3 Transport ......................................................................................... 10
2.2.4 Roasting Coffee ............................................................................... 10
2.2.5 Grinding and Brewing/Infusing ...................................................... 11
Economics of Coffee .............................................................................. 12
Bringing Coffee Home ........................................................................... 13
2.4.1 Coffee Origin and its Effect on Roasting ........................................ 13
2.4.2 The Problem with Coffee ................................................................ 14
2.4.3 A Small-Scale Shift ......................................................................... 14
3 The Science and Lore of Roasting Coffee ..................................................... 17
Pre-Roast Coffee/Coffee in General ....................................................... 17
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3.1.1 The Plant .......................................................................................... 17
3.1.2 The Cherry ....................................................................................... 17
3.1.3 The Coffee Bean .............................................................................. 18
The Science of Coffee Roasting ............................................................. 19
3.2.1 The Roast Progression ..................................................................... 19
3.2.2 The Not So Science of Coffee ......................................................... 20
The Lore of Coffee Roasting .................................................................. 20
3.3.1 Degree of Roast, Roasting, and End Point ...................................... 21
3.3.2 Roasting of a Drinkable Coffee ....................................................... 21
Roasting Technology .............................................................................. 22
Influential Works .................................................................................... 25
In Search of the Ideal Degree of Roast ................................................... 26
Researched Approaches that were not Possible to Test .......................... 28
3.7.1 Thermal Imaging ............................................................................. 28
3.7.2 Headspace Analysis ......................................................................... 29
Contextual Summary of Tested Measurement Approaches.................... 31
4 A Thermal Study of Coffee Roasting in a Fluidised Bed Coffee Roaster ..... 33
Chapter Introduction ............................................................................... 33
Building a Coffee Roaster ....................................................................... 34
4.2.1 Original Design ............................................................................... 35
4.2.2 Redesign .......................................................................................... 36
4.2.3 Temperature Measurement and Control .......................................... 40
Ramp Roasting Coffee ............................................................................ 42
4.3.1 Looking for Changes in Control Output .......................................... 44
4.3.2 Looking for Changes in Input Output Temperature Difference ...... 46
Bean Load ............................................................................................... 48
4.4.1 Calorimetry ...................................................................................... 48
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4.4.2 Inert Bean Load ............................................................................... 51
4.4.3 Coffee Bean Load ........................................................................... 53
4.4.4 Bean Load Analysis ........................................................................ 55
Modelling the Thermal Behaviour of Batch Roasted Coffee ................. 56
4.5.1 1-D model of coffee roaster ............................................................ 56
4.5.2 Evaporation Model Results and Comparison to Measured Data .... 66
4.5.3 Reanalysing Bean Load with the Reference Model ........................ 69
Conclusions ............................................................................................ 70
4.6.1 Detecting Second Crack .................................................................. 70
4.6.2 Final Thoughts and Improvements.................................................. 71
5 Online Microwave Moisture Measurement of Roasting Coffee .................... 73
Chapter Introduction and Summary ....................................................... 73
Microwave Measurement of Moisture ................................................... 74
Microwave Rig Setup ............................................................................. 75
5.3.1 Roasting Chamber Design............................................................... 75
5.3.2 System Setup and Changes ............................................................. 77
Initial Coffee Roast Measurements ........................................................ 78
Making Sense of the Data, the First Two Major Factors ....................... 81
5.5.1 Test on Varying Moisture Content .................................................. 81
5.5.2 Observing the Effect of Changing Temperature ............................. 83
Allowing for the Movement of the Coffee Beans .................................. 84
5.6.1 Possible Solutions ........................................................................... 85
5.6.2 Making Sense of the Movement Noise ........................................... 87
5.6.3 Result .............................................................................................. 96
Observing the Changes in a Coffee Roast .............................................. 98
5.7.1 What is Observed from the Coffee Roast? .................................... 101
Fitting to the Thermal Model ............................................................... 101
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Conclusions ........................................................................................... 106
6 Application of Raman Spectrometry ........................................................... 108
Chapter Summary ................................................................................. 108
Applying Raman Spectrometry to Coffee Roasting ............................. 110
6.2.1 Introduction to Raman Spectrometry ............................................ 110
Preliminarily Testing ............................................................................ 113
6.3.1 Single Bean Test ............................................................................ 113
6.3.2 Single Bean Result Analysis ......................................................... 115
Fluid Bed Application ........................................................................... 121
6.4.1 Focusing the Probe ........................................................................ 122
6.4.2 Fluid Bed Results .......................................................................... 124
6.4.3 Removing the Distortion ............................................................... 127
6.4.4 Online Roasting Measurements ..................................................... 131
Application of Thermal Model to Raman Data .................................... 135
Conclusions ........................................................................................... 135
7 Conclusions ................................................................................................. 138
Conclusions for the Master Roaster ...................................................... 139
8 References ................................................................................................... 141
9 Appendix ..................................................................................................... 147
Calorimetry Measurements on Ground Green Coffee .......................... 147
Stainless Steel Coffee Roasting Chamber............................................. 148
Bean Load Derivation ........................................................................... 151

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List of Figures
Figure 1. The coffee process and origin of coffee .................................................. 7
Figure 2. The coffee belt. [9] The region between the tropics where most of the
world’s coffee is grown. .......................................................................................... 9
Figure 3. Cluster of ripe coffee cherries on the tree ................................................ 9
Figure 4. Sacks of coffee beans ready for transport [12] ...................................... 10
Figure 5. Pan roasted coffee [18] .......................................................................... 11
Figure 6. Various brewing methods. Turkish, vacuum flask, French press, espresso
machine. [19]–[22] ................................................................................................ 12
Figure 7. Illustration of the coffee roasting process and it effect on coffee value 13
Figure 8. Comparison of commercial coffee roasting machine (left) with two home
roasting machines (right)....................................................................................... 15
Figure 9. Diagram of a coffee cherry, (based off diagram in Coffee Volume 1:
Chemistry[28]) ...................................................................................................... 18
Figure 10. Diagram of a drum coffee roaster, low speed hot air is blown through the
bottom of the drum. The drum rotates, moving the beans, ensuring an even roast.
............................................................................................................................... 22
Figure 11. Diagram of a fixed drum coffee roaster. The drum is heated from the
bottom while the coffee is agitated to ensure an even roast. ................................. 23
Figure 12. Diagram of fluid-bed (left) and spouted-bed (right) coffee roasters. High
speed hot air is blown through the coffee simultaneously agitating and roasting the
coffee. .................................................................................................................... 24
Figure 13. Initial conceptual design diagram of the fluid-bed coffee roaster. ...... 34
Figure 14. Original coffee roaster design. Based on popcorn popper. It could roast
coffee but unreliably. ............................................................................................ 36
Figure 15. Redesigned and built Coffee Roaster. In this figure, the roasting chamber
has been removed. This design was more reliable and allowed for the roasting
chamber to be replaced.......................................................................................... 38
Figure 16. Glass roasting chamber with roasted coffee. ....................................... 39
Figure 17. Functional diagram of the coffee roaster. Air is blown through the
heating element and into the coffee. Thermocouples linked to a computer logged
the air temperature at the input to the roast chamber, inside the coffee, and at the
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