Having backgrounds in traditional branches of chemistry (organic, analytical, physical), we now feel privileged to be writing about wine chemistry. Not only is wine chemistry a subject that inspires and challenges, it is also a wonderful vehicle for conversation – we often encounter colleagues, visitors and acquaintances who remark on how much they love wine and its complexity. That complexity can be intriguing but it can also be a barrier to further understanding, whether wine is a hobby or an occupation.
Wine chemistry is taught in a growing number of institutions as part of enology and viticulture curricula, as well as in traditional undergraduate chemistry departments as an elective course. Furthermore, there are many individuals in wine production and allied fields (e.g., suppliers) who expect to make science‐based decisions or recommendations. With this in mind, we identified the need for a book that could demonstrate to a reader how to utilize a basic knowledge of chemistry to rationally explain – and, better yet, predict – the diversity observed among wines.
Rather than providing only a description of wine constituents, or focusing on sensory characteristics, analytical aspects, or processing issues, we tackle the types of chemical and biochemical reactions that commonly occur in wine – in other words, we interpret winemaking outcomes through the lens of chemical principles. In doing this, 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 the major reactions that can occur in wine. We assume only a minimal prior knowledge of wine and winemaking, but do expect basic chemistry knowledge including organic chemistry, though we anticipate that our readers may have forgotten a lesson (or three) from these courses. At times we have relied on recent reviews rather than providing extensive citations to the literature, so we encourage the reader to seek out the primary sources of information to enhance their knowledge of any of the topics we have covered.
We approach our objectives by segregating the book into three parts.
To begin, we review the compound classes found in wine, their typical concentrations, their basic 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.
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 decisions made during winemaking will favor or disfavor 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 components on final wine composition. A feature on different bottle closures appears in Chapter 25.
To conclude, we present several case studies that relate the preceding sections to current or emerging areas of wine chemistry. With these examples we aim to demonstrate representative examples of the challenges – and opportunities – facing those who are interested in this amazing natural product called wine.
In preparing such a book we anticipate there will be gaps and errors, and we encourage the reader to send us comments with regard to anything. From simple typographical errors, to missing topics or citations, errors in data or interpretation, and even suggestions for new approaches to explaining wine chemistry, all suggestions are encouraged. We are planning to follow up with a second edition and any comments or ideas for improvement are most welcome. Please send your ideas to: winechem@ucdavis.edu.
In closing, we acknowledge the 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 our students who helped shape the book by reading draft chapters along the way. We also thank the grapegrowers and winemakers of the world for producing wines in a breathtaking range of styles – and thus chemistries – without which this topic and book would not exist. Lastly, we are eternally grateful to our partners and families who put up with our absence, or absentmindedness, and supported us throughout the process of publishing this book.