Understanding Wine Chemistry E-Book

Andrew L. Waterhouse

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 1404

Veröffentlichungsjahr: 2024

Beschreibung

Understanding Wine Chemistry Understand the reactions behind the world's most alluring beverages The immense variety of wines on the market is the product of multiple chemical processes - whether acting on components arising in the vineyard, during fermentation, or throughout storage. Winemaking decisions alter the chemistry of finished wines, affecting the flavor, color, stability, and other aspects of the final product. Knowledge of these chemical and biochemical processes is integral to the art and science of winemaking. Understanding Wine Chemistry has served as the definitive introduction to the chemical components of wine, their properties, and their reaction mechanisms. It equips the knowledgeable reader to interpret and predict the outcomes of physicochemical reactions involved with winemaking processes. Now updated to reflect recent research findings, most notably in relation to wine redox chemistry, along with new Special Topics chapters on emerging areas, it continues to set the standard in the subject. Readers of the second edition of Understanding Wine Chemistry will also find: * Case studies throughout showing chemistry at work in creating different wine styles and avoiding common adverse chemical and sensory outcomes * Detailed treatment of novel subjects like non-alcoholic wines, non-glass alternatives to wine packaging, synthetic wines, and more * An authorial team with decades of combined experience in wine chemistry research and education Understanding Wine Chemistry is ideal for college and university students, winemakers at any stage in their practice, professionals in related fields such as suppliers or sommeliers, and chemists with an interest in wine.

Leseprobe

Understanding Wine Chemistry

Second Edition

Andrew L. WaterhouseDepartment of Viticulture and EnologyUniversity of CaliforniaDavis, CA, USA

Gavin L. SacksDepartment of Food ScienceCornell UniversityGeneva, NY, USA

David W. JefferySchool of Agriculture, Food and WineThe University of AdelaideAdelaideSouth Australia

This second edition first published 2024© 2024 Andrew L. Waterhouse, Gavin L. Sacks, and David W. Jeffery. Published 2024 by John Wiley & Sons Ltd

Edition HistoryJohn Wiley & Sons Ltd (1e, 2016)

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The right of Andrew L. Waterhouse, Gavin L. Sacks, and David W. Jeffery to be identified as the authors of this work has been asserted in accordance with law.

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Library of Congress Cataloging‐in‐Publication Data

Names: Waterhouse, Andrew L., author. | Sacks, Gavin L., 1978- author. |  Jeffery, David W., 1972- author.Title: Understanding wine chemistry / Andrew L. Waterhouse, Department of  Viticulture and Enology, University of California, Davis, CA, USA, Gavin  L. Sacks, Department of Food Science, Cornell University, Geneva, NY,  USA, David W. Jeffery, School of Agriculture, Food and Wine, The  University of Adelaide, Adelaide, South Australia.Description: Second edition. | Hoboken : John Wiley & Sons Ltd., 2024. |  Includes index.Identifiers: LCCN 2024008704 (print) | LCCN 2024008705 (ebook) | ISBN  9781119894070 (hardback) | ISBN 9781119894087 (adobe pdf) | ISBN  9781119894094 (epub)Subjects: LCSH: Wine and wine making–Chemistry.Classification: LCC TP548.5.A5 W38 2024 (print) | LCC TP548.5.A5 (ebook)  | DDC 663/.2–dc23/eng/20240320LC record available at https://lccn.loc.gov/2024008704LC ebook record available at https://lccn.loc.gov/2024008705

Cover Design: WileyCover Image: Courtesy of Dr Duc‐Truc Pham

Foreword

In the realm of chemistry, where reactions often unfold in the blink of an eye, the world of wine stands as a fascinating exception. Wine evolves gradually, over years, which is exactly what makes its chemistry so complex. Not only will this book change how you think about wine, it will change the way you think about chemistry.

What flavors make the wine you love? The details embedded in its chemical compounds, from delicate isoprenoids (those floral and peppery aromas) to condensed tannins (that gripping, astringent sensation), tell us the story of the wine. Knowing these details is empowering, making you a more perceptive taster, able to pick up and explain more nuance.

Delving into the chemical makeup of wine is akin to discovering its genetic code. Understanding Wine Chemistry serves as a guide, explaining each major trait, from acidity to alcohol, and further exploring biochemical interactions during winemaking. By knowing wine's molecular identity, enthusiasts can gain confidence in discussing and appreciating wine, beyond the realm of casual enjoyment.

An understanding of wine chemistry allows winemakers to not only make better tasting, sound and stable wines, but also avoid mistakes. For example, it's an important responsibility to be wary of biogenic amines and know how to avoid or limit their production, or to control levels of volatile acidity, acetaldehyde, and sulfur dioxide for the safety and pleasure of friends and followers. This knowledge serves as a safeguard against pitfalls – especially the unknown unknowns – fostering an environment where science and craftsmanship entwine harmoniously, giving winemakers the tools and understanding to achieve their stylistic goals.

As with any scientific pursuit, there are limitations of current knowledge, which the book makes efforts to acknowledge. These gaps should inspire the curiosity of aspiring enologists.

Ultimately, Understanding Wine Chemistry will help all readers – from the casual enthusiast to the enology student to the veteran winemaker – approach wine as a scientist, capable of articulating the winemaking path that led to each sip.

Madeline PucketteFounder, Wine Folly

Preface

Our backgrounds in traditional branches of chemistry (organic, analytical, physical) have again been well‐utilized in preparing this second edition of Understanding Wine Chemistry. The first edition published in 2016 is in widespread use internationally by students, researchers, and practitioners, but – analogous to many wines – several sections were showing the unwanted effects of age after seven years. Wine chemistry is an active area of research and this second edition gives us a chance to share the latest knowledge, but also to rethink our approach to explaining difficult concepts.

Wine chemistry is routinely taught in a range of international institutions as part of enology and viticulture curricula, but can also be found in traditional undergraduate chemistry departments as an elective course. Aside from formal education settings, there are many individuals in wine production and allied fields who expect to make science‐based decisions or recommendations. These aspects inspired us to demonstrate to a reader how to utilize a basic knowledge of chemistry to rationally explain, or even better, predict the diversity observed among wines, and this overarching approach has been maintained in the second edition.

Although the book acts as a handy resource for researchers, it does not merely provide a description of wine constituents, nor solely focus on sensory characteristics, analytical aspects, or processing issues. In preparing this second edition, we had the collective insight that wine components could be best classified not only by the timing of their appearance (the common primary/secondary/tertiary language), but also by the timing of their disappearance (if any occurs). In the revised Introduction, and in collaboration with Madeline Puckette, we include what we hope to be an iconic figure depicting the evolution of exemplary wine components during fermentation and aging.

This new figure provides a snapshot of the dynamics of wine chemistry, with the causes of chemical changes being the focus of the book. We want to not only describe the components present in wine, but also to delve into chemical and biochemical reactions responsible for their formation and loss. With the approach taken, we aim to assist students, winemakers, and others in predicting the effects of wine treatments and processes or interpreting experimental results, based on an understanding of how the major reactions occur in wine. While ensuring the inclusion of seminal works, we have tended to rely on recent reviews rather than providing extensive citations to the literature, and therefore encourage the reader to seek out the primary sources of information to enhance their knowledge of any of the topics we have covered.

There is minimal assumed knowledge of wine and winemaking, but we do expect readers will have an understanding of basic chemistry, including organic chemistry. Nonetheless, we anticipate that readers may require some refresher regarding the knowledge gained from previous chemistry courses. For experienced chemists, some basic background information provided in the book may seem excessive in places, but our goal was to produce a resource that was accessible to the majority.

As with the previous edition, we approach our objectives by separating the book into three parts.

Part A

, Wine Components

To begin, we review the compound classes found in wine, their typical concentrations, their chemical reactivities, and their contribution to wine stability or sensory characters. This first part also considers the types of reactions that components can undergo in a wine environment, and is designed to be used as a reference for subsequent sections. Key chemical concepts involving electrophiles and nucleophiles, and electrophilic aromatic substitution are featured in Chapters 10 and 14, respectively. While all chapters have been revised and updated, significant modifications in this part involve the chemistry of sulfur compounds (Chapter 10) and sulfur dioxide (Chapter 17).

Part B

, Chemistry of Winemaking

Following a brief overview of grape composition and wine production practices, we describe the key reactions that occur during and after fermentation. In particular, we highlight how winemaking decisions will influence certain chemical reactions, leading to differences in wine composition. We expect that this part can be used to generate hypotheses regarding the effect of unfamiliar winemaking processes or changes in juice/must components on final wine composition. Information on S‐conjugates and thiol formation in Chapter 23.2 has been expanded and redox chemistry described in Chapter 24 has undergone substantial refinement. Additional information on oak barrels and oak alternatives has been included in Chapter 25, along with updates to the sensory effects of aging conditions. A feature on different bottle closures also appears in Chapter 25.

Part C

, Special Topics

To conclude, we present new case studies in this edition that relate the preceding sections to current or emerging areas of wine chemistry. With these examples, which encompass natural wine, novel packaging materials, synthetic wine, and alternative ways to age wine, we aim to demonstrate representative examples of the challenges – and opportunities – still facing those who are interested in this amazing natural product called wine. Chapters on authentication and wine analysis have been retained, but modified to include some of the latest methodological and instrumental advances of relevance to wine research.

The first edition preface included the statement “Wine chemistry continues to be a subject that inspires and challenges, and although it involves substantial complexity, gaining further understanding is not beyond any reader…” Over the last seven years, we humbly learned that this statement also applies to us, the authors. In this second edition, we have eliminated a range of errors from the first edition, many of which were brought to our attention by careful readers. We expect that this second edition will include additional new gaps or oversights and we encourage our readers to alert us to typographical mistakes, errors in data or interpretation, and even suggestions for worthy topics or approaches to include in future editions.

In closing, we acknowledge the ongoing work of the many researchers in the international wine science community that we have drawn upon in formulating this book, and also appreciate the feedback from students and colleagues who helped shape the second edition. Dr Paul Bowyer is acknowledged for reviewing the chapter on filtration. We also thank the grapegrowers and winemakers of the world for continuing to produce wines in a breathtaking range of styles – and thus chemistries – despite the ever increasing challenges they face. Lastly, we express our eternal gratitude to our partners and families who have once again put up with our preoccupation with our other love, that of wine chemistry. Without their ongoing support and understanding, publishing this revised edition would not have been possible.

Andrew L. WaterhouseUniversity of California, Davis

Gavin L. SacksCornell University

David W. JefferyThe University of Adelaide

Introduction

The chemical diversity of wine

How many choices does a consumer have when they buy a wine? In the United States, all packaged wines must have a Certificate of Label Approval (COLA) from the Alcohol and Tobacco Tax and Trade Bureau (TTB). In 2023, the TTB approved COLA requests for approximately 30 000 white table wines, 40 000 red table wines, 10 000 sparkling or carbonated wines (including Champagne), and tens of thousands of dessert, rosé, fruit, and flavored wines.1 Because many wines are vintage products with an identical label (other than harvest year, and thus not requiring review) for each year, and many wines produced internationally are not imported into the US, the true number of wines available at any instance is even greater. An online wine marketplace (Wine Searcher) listed 6.8 million different wines in 2015 [1], and this quantity has almost certainly grown. In contrast to commodities where producers strive for homogeneity (e.g., wheat flour and milk), variation in specialty products like wine is not merely tolerated – it is appreciated and celebrated. Consumers expect that wines with different labels should smell different, taste different, and look different; from a chemist's perspective, consumers expect wines to have different chemical compositions. The study of wine chemistry is the study of these differences, explaining how there can be hundreds of thousands, if not millions, of different wine compositions, and contributing to a winemaker's understanding of how the myriad of choices they are faced with can lead to such diversity.

What is wine?

While wine is often described in poetic terms, such as sunlight in a glass, a chemical description for dry table wine is a mildly acidic (pH 3–4) hydroalcoholic solution. The two major wine components are water and ethanol, typically accounting for about 97% on a weight‐for‐weight (w/w) basis. The remaining compounds – responsible for most of the flavor and color of wine – are typically present at <10 g/L total (Figure I.1), and many key odorants are found at part‐per‐trillion (ng/L) concentrations! Notably, none of these compounds appear to be unique to wine – compounds present in wine can also be found in coffee, beer, bread, spices, vegetables, fruits, cheese, and other foodstuffs.2 What distinguishes different wines from other products (and each other) is differences in the relative concentrations of compounds resulting in different flavors, rather than the presence of unique components.

Figure I.1 Composition of a representative dry red table wine (a) on a % w/w basis and (b) typical concentrations (mg/L) of major wine components excluding water and ethanol, that is, the main contributors to “Everything else”. Key trace components (0.1 ng/L–10 mg/L) would not be visible and are therefore not included. Chemists: note that 11% w/w ethanol is approximately 13.9% v/v ethanol, with the latter units being almost exclusively used to express ethanol concentration as well as appearing on wine labels

Wine is produced by the alcoholic fermentation of grape juice or must (juice and solids), which results in the complete or partial transformation of grape sugars to ethanol and CO2. The use of other fruits must be declared, i.e., “Raspberry Wine”. However, winemaking and wine storage result in many chemical changes beyond simply the consumption of sugars and formation of alcohol. This is readily exemplified by the greater complexity of volatiles in wine as compared to grape juice (Figure I.2). An array of volatile components can contribute to the aroma of wine, and these “odorants” are sometimes classified based on when they are formed; that is, in the grape (primary), during fermentation (secondary), or during maturation and storage (tertiary) (Table I.1). Many wine components do not neatly fall into only one category – monoterpenes like linalool (“floral” aroma; Chapter 8), for example, may be found in grapes (primary flavor compound) but may also be formed from precursors during fermentation (secondary). Complicating this further, non‐volatile varietal thiol precursors from grapes release their odiferous forms during alcoholic fermentation (Chapter 23.2), and thus are considered “secondary” rather than “primary” odorants. However, the free compounds are called “varietal” thiols (Chapter 10) because they can be linked to specific, cultivar‐dependent precursors.

Figure I.2 Comparison of GC‐MS chromatograms for (a) a grape juice and (b) a wine produced from that grape juice. Every peak in the chromatograms represents at least one unique volatile compound. Note that the relative size of a peak does not necessarily relate to the importance of that compound to wine aroma – many important odorants might scarcely be seen on the baseline

Table I.1 Primary, secondary, and tertiary classifications of wine odorants and representative examples of each class

Compound classification

a

Description

Example

Primary

  Compounds present in grape must or juice that persist unchanged into wine

 Methoxypyrazines (

Chapter 5

), rotundone (

Chapter 8

), monoterpenes (

Chapter 8

)

Secondary

  Compounds formed as a result of alcoholic or malolactic fermentation due to either

(i) Normal metabolism of sugars, amino acids, etc.

(ii) Transformation of grape‐specific precursors

(i) Ethyl esters (

Chapter 22.2

), fusel alcohols (

Chapter 22.3

)

(ii) Monoterpenes (

Chapter 8

), varietal thiols (

Chapter 23.2

)

Tertiary

  Compounds formed during wine storage, for example, as a result of

(i) Extraction from oak

(ii) Microbial spoilage or chemical tainting

(iii) Abiotic transformation of precursor compounds in wine

(i) Oak lactones (

Chapter 25

)

(ii) Trichloroanisole (

Chapter 18

)

(iii) 1,1,6‐Trimethyl‐1,2‐dihydronaphthalene (TDN) (

Chapter 23.1

)

aCompounds may be members of more than one class.

Many non‐volatile components are also extracted and reacted during winemaking, along with the suite of volatiles, with the number of compounds identified following advances in analytical technology. A survey from 1969 reported that wine and other alcoholic beverages contained 400 volatiles, while a later book from 1983 reported over 1300 volatiles [2]. A more recent analysis of wines using a state‐of‐the‐art mass spectrometry system (FT‐ICR‐MS) was able to detect tens of thousands of unique chemical signals across a set of wines, and assign chemical formulae to almost 9000 components (mostly non‐volatiles such as amino acids, carbohydrates, and phenolics) [3]. However, the advanced instrumentation in that report would not distinguish structural isomers – for which there may be millions for a condensed tannin consisting of 10 monomers [4] (Chapter 14). Although technology is still advancing, even the extra dimension of resolution offered by emerging techniques, for example, the coupling of mass spectrometry with ion mobility spectroscopy or 2‐dimensional chromatography (Chapter 32