Understanding Wine Chemistry

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

Adelaide, USA. David Jeffery received his PhD in synthetic organic chemistry from Flinders University, and has been involved with wine chemistry for over a decade, initially as a researcher at The Australian Wine Research Institute before transitioning to The University of Adelaide in 2010. He teaches wine chemistry to undergraduate and Master level students, delivering topics associated with stabilization, clarification, distillation, wine aroma, polyphenols, and analytical methods. He also helped to develop and deliver a free online wine education course called Wine 101x, offered on the EdX platform. David's research areas extend to on many aspects of wine chemistry, with special interests in polyphenols and aroma compounds and their precursors. He utilizes his expertise in synthetic organic chemistry and natural product isolation, purification and characterization, along with experience in developing and applying analytical methods, to improve understanding of grape and wine chemistry, particularly in relation to chemical composition and quality.