Wine Faults and Flaws. Keith Grainger

to the market very quickly, sometimes within a few months of harvest. Time is money, and there may be little time or budget for all desirable stabilisation procedures to take place. Finally, the consumer and especially the serious wine lover, wants wine to be a natural, agricultural product that has been turned into something wonderful by an artisan, not a scientist. Accordingly, many producers strive to make wine as ‘natural’ as possible, by reducing interventionist techniques and minimising chemical and biological additions, including those that may increase stability and prevent the onset of certain faults. It is also of concern that there is an increase in the incidence of mycotoxins in wines, due to their production by some of the microbial populations on vines. This is perhaps another consequence of climate change. Related off‐flavours, which were historically noted only occasionally, have been detected at a much higher frequency during the last 15 years.

      This book provides a detailed examination and explanation of the causes and impact of the faults, flaws, and taints that may affect wines. As such, I believe that it will prove particularly valuable to winemakers, especially those at small, boutique wineries, wine technologists and quality control professionals. Wine critics, writers, educators, and sommeliers will also find the topics most relevant. With wine trade students and people venturing into the business of wine production in mind, the content is designed to be easily and speedily assimilated. The interested and knowledgeable wine‐loving consumer, including wine collectors and investors, will also find the book highly relevant and the basis for discussion at many tastings with like‐minded associates.

      It is assumed that the reader has, at least, a basic knowledge of winemaking. Those who feel the need to brush up on the methods and techniques of wine production, from vine to bottle, are referred to ‘Wine Production and Quality 2nd Edition’ by Keith Grainger and Hazel Tattersall, also published by Wiley. However, this book is very suitable for those with limited scientific knowledge, and I have made every effort to maximise readability, with many anecdotes and expressed opinions, including my own. The chasm between general and scientific wine publications is both wide and deep, and I have attempted to bridge this as soundly as possible. There are several excellent books on viticulture and oenology, written in scientific language. Some of these are listed in the Further Reading. Alternatively, the easy to read articles and books penned by wine writers are seen by the scientific community as overflowing with anecdotes and lacking rigour. Of course, both approaches are valid, and I have made every effort to integrate them. I have tried to speak in terms that the general reader can understand. Although the number of studies and quality of research into chemical and microbiological faults in wine has increased considerably in the last couple of decades, most of this work remains within the confines of journals, which are largely unread outside of scientific and academic communities. On many occasions, results are inconclusive, conflicting, or the focus of some studies is seen as so narrow as to be of little relevance in the real world. Indeed many of the winemakers I have spoken to whilst researching this book have not been aware of the outcomes of recent research in important areas. Accordingly, there is still much misinformation and misunderstanding of the topics by producers, students and, of course, consumers.

Sections of individual chapters cover the science behind each fault, and for these, a very basic knowledge of organic chemistry and microbiology would be valuable. However, the scientifically challenged reader will find the text in includes helpful explanations, and the Glossary contains easy to understand definitions and descriptions of many scientific terms. I have included, at the end of each chapter, references to relevant publications and research papers (over 800 in total), concentrating on those in English and published within the last 20 years. I have also included references to earlier research that was particularly ground‐breaking. I have not included structural drawings, and there are very few chemical equations. I have not generally detailed isomers (isomers are where compounds have the same formula but differ from each other in the way the atoms are arranged). As the title of this work suggests, the focus is very much on practice – the book is certainly not aimed at the research scientist. In other words, I wish it to be a helpful manual for those who have little interest in the activities of the research lab, but to whom the excitement and challenges of the real world of wine are a way of life.

      Keith Grainger

      Saint‐André‐de‐Lidon

      19 August 2020

Introduction

      This book comprises a detailed examination of faults, flaws, and taints that can affect the quality and merchantability of wines. Technically, there is a distinction between a taint and fault that will be discussed in Chapter 1. However, wine consumers, merchants, and the press rarely observe such distinction, simply referring to the affected product as faulty. Some faults render affected wines unsaleable and undrinkable. Others that have a negative effect upon quality, enjoyment, or potential for ageing.

      There are no reliable figures regarding the total global financial cost of faulty and tainted wines to producers, agents, distributors, and retailers. However, there can be no doubt that it runs into many £/€ billions annually. A recent estimate of the economic costs to EU wine producers of haloanisoles taint in wines (so‐called ‘cork taint’) is 700 million euros annually [1]. Product recalls due to matters other than incidences of physical contamination are relatively rare in the wine industry. When bottles of faulty wines do reach the consumer, the impact upon the producers' and suppliers' reputations is incalculable. Although the purchaser may not have the knowledge or skill to identify the fault in question, it is unlikely that they will repurchase any other bottles of the same wine, and may avoid the brand or producer in question. In other words, the consumer will believe the faulty wine to be very low quality. If they have no recourse to financial redress, as will most likely be the case for wines purchased many years previously and which they have been patiently nurturing in their ‘cellar’ in anticipation of the complex delights of full maturity, consumers may well feel somewhat cheated.

Wine is, without doubt, the most discussed food or drink in the world, and wine lovers readily communicate their experiences to friends, colleagues, and those who share a love for what can be the most exciting and individual of products. Today, such discussions are livelier and more influential than ever. With the proliferation of blogs and social media postings, the opinions of a consumer's peers are, for better or worse, as or even more important than those of professional critics and reviewers. Wine writers, authors, and journalists are generally hugely supportive of the wine industry, without which their profession would not exist. Most are ‘deeply in love’ with wine, or at least ‘fine wine’. However, it is the nature of writing that certain topics become ‘hot’ and are then developed and pursued for as long as the readership retains an interest. Amongst the wine faults that have received considerable coverage in specialist consumer media in the last decade or two are so‐called ‘cork taint’, ‘reduced’ aromas (often referred to as reduction or reductivity), premature oxidation (premox), and the aromas produced by Brettanomyces yeasts. When such topics are discussed in a global context, articles can be informative, but they can also weaken confidence and influence buying habits. However, if the coverage relates to individual producers, the damage inflicted can be both instant and ongoing. Reputational damage may be done simply by naming faulty wines submitted for assessment at comparative tastings conducted by specialist magazines, or for tasting competitions. By way of example, during the early years of this century, the influential USA published magazine Wine Spectator revealed the identity and details of several ‘high‐end’ Californian producers who had marketed wines tainted by 2,4,6‐trichloroanisole (TCA) and 2,4,6‐tribromoanisole (2,4,6‐TBA). These compounds are usually, and particularly in the case of 2,4,6‐TBA erroneously, referred to as ‘cork taint’. The negative impact upon the reputations of producers that had taken decades to build is apparent.

      On the other hand, there are ‘under the radar’ faults that are seldom discussed in the popular wine media or amongst professionals. A prime example is ‘atypical ageing’, by which white wines very rapidly lose varietal character and develop undesirable aroma and palate characteristics. This fault, often confused with premature oxidation, has been described as