Wine chemistry inspires and challenges with its complexity, and while this is intriguing, it can also be a barrier to further understanding. The topic is demystified in Understanding Wine Chemistry, Special Mention awardee in the 2018 OIV awards, which explains the important chemistry of wine at the level of university education, and provides an accessible reference text for scientists and scientifically trained winemakers alike.
Understanding Wine Chemistry:
- Summarizes the compounds found in wine, their basic chemical properties and their contribution to wine stability and sensory properties
- Focuses on chemical and biochemical reaction mechanisms that are critical to wine production processes such as fermentation, aging, physiochemical separations and additions
- Includes case studies showing how chemistry can be harnessed to enhance wine color, aroma, flavor, balance, stability and quality.
This descriptive text provides an overview of wine components and explains the key chemical reactions they undergo, such as those controlling the transformation of grape components, those that arise during fermentation, and the evolution of wine flavor and color. The book aims to guide the reader, who perhaps only has a basic knowledge of chemistry, to rationally explain or predict the outcomes of chemical reactions that contribute to the diversity observed among wines. This will help students, winemakers and other interested individuals to anticipate the effects of wine treatments and processes, or interpret experimental results based on an understanding of the major chemical reactions that can occur in wine.
Table of Contents
Foreword xiii
Preface xv
Introduction xvii
The chemical diversity of wine xvii
What is wine? xvii
Chemical reactions in wine xx
Chemistry as a historical record xxi
The chemical senses and wine flavor xxi
References xxiv
Part A Wine Components and Their Reactions 1
1 Water and Ethanol 3
1.1 Introduction 3
1.2 Chemical and physical properties of water 3
1.3 Properties of ethanol and ethanol–water mixtures 4
1.4 Typical ethanol concentrations in wines 6
1.5 Sensory effects of ethanol 7
References 9
2 Carbohydrates 11
2.1 Introduction 11
2.2 Nomenclature, representation, and occurrence of sugars 11
2.3 Physical, chemical, and sensory properties of sugars 14
2.4 Polysaccharides 17
References 18
3 Acids 19
3.1 Introduction 19
3.2 Organic acids in wine 19
3.3 Organic acids, pH, and wine acidity 21
3.4 Acid adjustments 28
3.5 General roles of organic acids and pH in wine reactions 31
3.6 Sensory effects of acids 31
References 32
4 Minerals 34
4.1 Introduction 34
4.2 Origins of metals in wine 35
4.3 Reactions involving metals 35
4.4 Sensory effects of metals 37
4.5 Metals and wine authenticity 37
References 38
5 Amines, Amino Acids, and Proteins 40
5.1 Introduction 40
5.2 Chemistry of amines 40
5.3 Amino acids and related major nitrogenous compounds in wines 41
5.4 Nitrogenous compounds with health effects 44
5.5 Odor-active amines 45
References 48
6 Higher Alcohols 51
6.1 Introduction 51
6.2 Properties of higher alcohols 51
6.3 Origins and concentrations of higher alcohols 52
6.4 Six-carbon (C6) alcohols 53
6.5 Methanol 54
References 55
7 Esters 57
7.1 Introduction 57
7.2 Chemistry of esters 57
7.3 Esters in grapes 60
7.4 Esters formed during winemaking and storage 60
7.5 Sensory effects 65
References 66
8 Isoprenoids 68
8.1 Introduction 68
8.2 General chemical and sensory properties of isoprenoids 68
8.3 Monoterpenoids 69
8.4 Sesquiterpenoids 73
8.5 C13-Norisoprenoids 74
References 76
9 Aldehydes, Ketones, and Related Compounds 79
9.1 Introduction 79
9.2 Acetaldehyde 80
9.3 Short and medium chain aldehydes 80
9.4 Complex carbonyls 84
9.5 Carbonyl reactivity 85
References 86
10 Thiols and Related Sulfur Compounds 88
10.1 Introduction 88
10.2 Varietal sulfur aroma compounds – polyfunctional thiols 91
10.3 Fermentative sulfur aroma compounds 93
10.4 Other sulfur-containing aroma compounds 94
Chemical principles: nucleophiles and electrophiles 95
References 97
11 Introduction to Phenolics 99
11.1 Introduction 99
11.2 Non-flavonoids 102
11.3 Flavonoids 103
References 104
12 Volatile Phenols 105
12.1 Introduction 105
12.2 Structure and chemical properties 105
12.3 Concentrations in wine and sensory effects 107
12.4 Origins in wine and effects on volatile phenol profile 107
References 110
13 Non-flavonoid Phenolics 112
13.1 Introduction 112
13.2 Hydroxycinnamates 112
13.3 Hydroxybenzoic acids 113
13.4 Stilbenes 114
References 115
14 Flavan-3-ols and Condensed Tannin 117
14.1 Introduction 117
14.2 Monomeric catechins 117
14.3 Oligomeric proanthocyanidins and polymeric condensed tannins 119
14.4 Sensory effects 122
Chemical principles: electrophilic aromatic substitution 123
References 125
15 Flavonols 127
15.1 Introduction 127
15.2 Concentrations of flavonols 127
15.3 Effects of growing conditions and winemaking 129
References 129
16 Anthocyanins 131
16.1 Introduction 131
16.2 Structures and forms 131
16.3 Non-covalent interactions: co-pigmentation 133
16.4 Bisulfite bleaching 134
16.5 Wine pigments 135
References 138
17 Sulfur Dioxide 140
17.1 Introduction and terminology 140
17.2 Acid–base chemistry of SO2 141
17.3 Sulfonate adducts, “bound SO2,” and antioxidant effects 143
17.4 Typical sources and concentrations of SO2 in wine 146
17.5 Measurement of molecular, free, and total SO2 146
17.6 Sensory effects 147
References 148
18 Taints, Off-flavors, and Mycotoxins 149
18.1 Introduction 149
18.2 Common wine taints 150
18.3 Off-flavors in wine 155
References 156
Part B Chemistry of Wine Production Processes 159
19 Outline of Wine Production 161
19.1 Introduction 161
19.2 Basic workflow 161
19.3 Processes involved 164
19.4 Tanks and fermenters 166
19.5 Beyond fermentation 169
19.6 Specialty wines 169
References 170
20 Grape Must Composition Overview 172
20.1 Sampling 172
20.2 Sugars 172
20.3 Acids 173
20.4 Phenolics 174
20.5 Nitrogen species 175
20.6 Lipids and waxes 175
20.7 Minerals and vitamins 176
20.8 Isoprenoids 176
20.9 Insoluble materials 176
References 177
21 Maceration and Extraction of Grape Components 179
21.1 Introduction 179
21.2 Pre-fermentative treatments 183
21.3 Maceration treatments during fermentation 186
21.4 Post-fermentation maceration 189
References 190
22 The Biochemistry of Wine Fermentations 194
22.1 Glycolysis 195
22.1.1 Introduction 195
22.1.2 Glycolysis and alcoholic fermentation 196
22.1.3 Glyceropyruvic fermentation 198
22.1.4 Succinic acid and other Krebs cycle intermediates 200
22.1.5 Consequences of glycolysis on wine chemistry 202
References 204
22.2 Fatty Acid Metabolism 205
22.2.1 Introduction 205
22.2.2 Long-chain fatty acid metabolism 205
22.2.3 Mid-chain fatty acids (MCFAs) and ethyl esters 209
22.2.4 Increasing MCFA and their ethyl esters in winemaking 211
References 212
22.3 Amino Acid Metabolism 214
22.3.1 Introduction 214
22.3.2 Nitrogen uptake and catabolite repression 214
22.3.3 Amino acid anabolism, catabolism, and carbon skeletons 216
22.3.4 Higher alcohol formation 216
22.3.5 Acetate ester formation 218
22.3.6 YAN in the winery – requirements, approaches, and consequences 219
References 221
22.4 Sulfur Metabolism 223
22.4.1 Introduction 223
22.4.2 Sulfide production and assimilation 223
22.4.3 Nitrogen sources and H2S formation 226
22.4.4 Timing of formation and residual H2S 227
References 228
22.5 Bacterial Fermentation Products 230
22.5.1 Introduction 230
22.5.2 Lactic acid bacteria 230
22.5.3 Spoilage of wine by bacteria 235
References 237
23 Grape-Derived Aroma Precursors 239
23.1 Glycosidic Precursors to Wine Odorants 240
23.1.1 Introduction 240
23.1.2 Formation of glycosidic aroma precursors in grape berries 242
23.1.3 Glycosidic aroma precursors – extraction 245
23.1.4 Hydrolysis of glycosidic aroma precursors – mechanisms 246
23.1.5 Hydrolysis of glycosides under fermentation and aging conditions 249
References 252
23.2 S-Conjugates 256
23.2.1 Introduction 256
23.2.2 Formation of S-conjugate precursors in berries and juice 257
23.2.3 Conversion of S-conjugate precursors during fermentation 259
23.2.4 Mass balance and alternative pathways to volatile thiol formation 262
References 263
23.3 Conversion of Variety Specific Components, Other 265
23.3.1 Introduction 265
23.3.2 Polyunsaturated fatty acid precursors of C6 compounds 265
23.3.3 Hydroxycinnamic acids, Brettanomyces, and volatile phenols 269
23.3.4 S-methylmethionine and dimethyl sulfide 273
References 275
24 Wine Oxidation 278
24.1 Introduction 278
24.2 Redox reactions 278
24.3 The central tenets of wine oxidation 280
24.4 The central tenets of quinone reactions 283
24.5 The central tenets of the Fenton reaction and byproducts 288
References 291
25 Topics Related to Aging 294
25.1 Introduction 294
25.2 Reactions involving red wine pigments 294
25.3 Hydrolytic and pH-dependent reactions 298
25.4 Activation energy and temperature effects on aging 303
25.5 Effects of oak storage 304
25.6 Sensory effects of different aging conditions 309
Closure performance 312
References 313
26 The Chemistry of Post-fermentation Processing 318
26.1 Cold Stabilization 319
26.1.1 Introduction 319
26.1.2 KHT crystal properties and solubility 320
26.1.3 Critical factors for KHT precipitation 322
26.1.4 Testing for KHT stability 325
26.1.5 Treatments for preventing KHT precipitation 327
26.1.6 CaT and related precipitates 330
References 330
26.2 Fining 332
26.2.1 Introduction 332
26.2.2 Tannin fining with proteins 333
26.2.3 Protein fining with bentonite 338
26.2.4 Miscellaneous fining and related treatments 341
References 343
26.3 Particle Filtration and Reverse Osmosis 346
26.3.1 Introduction 346
26.3.2 Definitions, principles, and characteristics of winery filtration 347
26.3.3 Filtration and fouling 350
26.3.4 Reverse osmosis 354
26.3.5 Sensory effects of filtration 355
References 357
26.4 Distillation 359
26.4.1 Introduction 359
26.4.2 Vapor–liquid equilibria 360
26.4.3 Batch and continuous distillation 365
26.4.4 Spirit composition and cask maturation 373
References 375
27 Additives and Processing Aids 377
27.1 Introduction 377
27.2 Regulations and terminology 377
27.3 Additives and processing aids: functions and comparison across regions 379
References 382
Part C Case Studies: Recent Advances in Wine Chemistry 383
28 Authentication 385
28.1 Introduction 385
28.2 Fraud – categories and detection approaches 385
28.3 Stable isotope ratio analysis to detect glycerol adulteration 387
28.4 Future challenges in wine authentication 389
References 390
29 Optimizing White Wine Aromas 392
29.1 Introduction 392
29.2 Enhancement of varietal thiols 392
29.3 Cofermentation and spontaneous fermentation 394
References 395
30 Appearance of Reduced Aromas during Bottle Storage 397
30.1 Introduction 397
30.2 Potential latent sources of compounds responsible for reduced aromas 397
References 399
31 Grape Genetics, Chemistry, and Breeding 400
31.1 Introduction 400
31.2 Breeding new varieties 400
31.3 Genetics and selection 402
References 403
32 Analytical Innovations and Applications 404
32.1 Introduction 404
32.2 Typical approaches to wine analysis 405
32.3 Multivariate data analysis and chemometrics 408
32.4 Chemometrics in practice – rapid methods for wine analysis 409
32.5 Targeted and untargeted metabolomics of wine 413
References 414
33 New Approaches to Tannin Characterization 417
33.1 Introduction 417
33.2 The challenge of astringency subclasses 418
References 418
Index 420
