Wine Faults and Flaws

A Practical Guide

Keith Grainger

• Publisher: Wiley-Blackwell
• Year: 2021
• Print ISBN: 9781118979068
• eBook ISBN: 9781118979075
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

2022 Winner of the OIV Award in the Oenology category

An essential guide to the faults and flaws that can affect wine

Written by the award-winning wine expert, Keith Grainger, this book provides a detailed examination and explanation of the causes and impact of the faults, flaws and taints that may affect wine. Each fault is discussed using the following criteria: what it is; how it can be detected by sensory or laboratory analysis; what the cause is; how it might be prevented; whether an affected wine is treatable, and if so, how; and the science applicable to the fault.

The incidences of faulty wines reaching the consumer are greater than would be regarded as acceptable in most other industries. It is claimed that occurrences are less common today than in recent recorded history, and it is true that the frequency of some faults and taints being encountered in bottle has declined in the last decade or two. However, incidences of certain faults and taints have increased, and issues that were once unheard of now affect many wines offered for sale. These include 'reduced' aromas, premature oxidation, atypical ageing and, very much on the rise, smoke taint.

This book will prove invaluable to winemakers, wine technologists and quality control professionals. Wine critics, writers, educators and sommeliers will also find the topics highly relevant. The wine-loving consumer, including wine collectors will also find the book a great resource and the basis for discussion at tastings with like-minded associates.

Reviews
I read this book avidly from cover to cover. I'll dip into it for future reference as required, which is how many will employ it. Meanwhile, I learned a great deal, and it now influences how I think about wine evaluation.
I commend this excellent new book to you. Consider it an investment. Paul Howard, Wine Alchemy

1
Faults, Flaws, Off‐Flavours, Taints, and Undesirable Compounds

In this chapter, the advances in wine technology and changes in the markets in the recent decades are discussed, along with the possible adverse impacts of some wine compounds on human health. The distinction, often made generally in the food industry, between ‘faults’ and ‘taints’ has limited validity in wines. The challenges of sensory detection thresholds of fault compounds are noted. Microbiological and chemical faults are distinguished, and the boundary between, ‘flawed’ and ‘faulty’ is discussed. At the end of the chapter, I consider whether faulty wines can be paradoxically excellent.

1.1 Introduction

The origin of any fault or flaw in wine may be chemical, microbiological, or physical. During the process of winemaking, thousands of biochemical reactions are taking place, and most of them contribute to the aroma and flavour profile of the wine, but some are unwanted and, if not controlled or inhibited, quality will be compromised and off‐odours or faults may develop. The diverse interactions between yeasts, fungi, bacteria, and chemical compounds begin in the vineyard and continue through the production processes including maturation and even during storage after packaging. The alcohol in wine (ethanol), together with the acids, provide some stability and protection against deterioration – in fact, wine (as opposed to grape must) is a harsh environment for microbes, thereby allowing only relatively few to grow. However, some microorganisms, including unwanted yeasts and bacteria can flourish during winemaking and may remain in a wine that has finished all stages of production and cause off‐odours, off‐flavours, or product deterioration months, or even years, after bottling. Wine may become contaminated and develop such off‐odours and flavours as a result of external factors during the production processes, and even subsequent to bottling or other packaging. Common sources of contaminants include processing aids (e.g. bentonite), the winery or cellar atmosphere and environment, packaging materials (including bottle closures), and transport or storage facilities (including shipping containers).

1.2 Advances in Wine Technology in Recent Decades

The origins of wine production date back 8000 years, but the advances in the science and technology of production since World War II have outstripped those of the previous 79 centuries. There have been huge changes in the methods and improvements in standards of viticulture, although the reliance upon chemical fertilisers, pesticides, and herbicides that began in the 1960s declined only recently and was certainly both damaging to the environment and wine quality. The recent advent of geolocating and remote and proximal sensing and soil mapping, so‐called ‘precision viticulture’, and techniques to determine the hydric stress of vines have enabled growers to fine tune site‐specific management practices, including the precise addition of desirable nutrients and, where permitted, measured quantities of adjusted irrigation water to individual vineyard blocks, or even precise parts of blocks.

In the winery there have been numerous advances in equipment design and quality, and winemaking procedures. Some of the most important of these are:

• Grape sorting and selection systems to exclude unripe, rotten, or damaged fruit: spectacular innovations have been made in the technology of sorting equipment in the last 15 years, including the use of sophisticated optical sorters;
• The widespread utilisation from the 1970s of temperature‐controlled fermentation vessels (usually constructed of easily cleanable AISI 316 or 304 grade stainless steel), although the move today is ‘back’ to vats made of wood or concrete;
• Development of numerous individual strains of cultured yeasts aiding the control of fermentations and development of required flavours;
• A detailed understanding of malolactic fermentation (MLF) and the development of suitable inoculums for use when deemed necessary;
• The utilisation of a wider range of extraction techniques including pre‐fermentation cold soaks, rack, and return (délestage), flash détente and thermo détente;
• The use of gases namely carbon dioxide, nitrogen, and argon, primarily to avoid unwanted oxidation;
• The development of programmable enclosed pneumatic presses that can be gas‐flushed;
• The utilisation of in‐tank micro‐oxygenation, particularly for inexpensive red wines, that helps polymerise long‐chain tannins and is a valuable tool if costly barrel ageing is not to take place;
• Pre‐bottling cold stabilisation, often also using the ‘contact process’, to precipitate crystals of potassium bi‐tartrate or calcium tartrate. Alternatively, membrane electrodialysis may now be employed for this purpose;
• The availability of systems employing membrane technology, for must and wine correction, and filtration, including front end microfiltration (MF), cross‐flow (tangential) MF, ultrafiltration (UF), reverse osmosis (RO), and pervaporation;
• the improvement in cork closure quality, particularly regarding the cleansing of corks of 2,4,6‐trichloroanisole (TCA), and the introduction of effective alternative closures, including screw‐caps and synthetic closures with determined oxygen transmission rates (OTRs).

Of course, small‐ and medium‐scale producers, many of whom are focussed upon the individuality and quality of their wines, may choose not to utilise ‘advanced’ techniques in the vineyard or winery, including oenological additives, processing aids, or sophisticated (and expensive) technical equipment.

1.3 Changes in Markets and the Pattern of Wine Consumption in Recent Decades

The changes in the pattern of wine consumption of wine during the last 40 years have been dramatic. There has been spectacular growth in sales in many countries that have limited domestic production and accordingly rely upon imports to satisfy demand: for example, in the United Kingdom, per capita wine consumption rose from just 2 l in the early 1960s to 19.7 l in 2010–2016 [1]. In 2018, UK per capita consumption was approximately 24.6 l [2]. However, during the same period, the per capita consumption of many traditional European wine production countries declined by some 50%, albeit mostly of very low quality wines. Prior to the 1970s only 10% of all wines were exported from producing countries, including intra‐Europe ‘exports’; by 2016 over one‐third of wine consumed globally was produced in another country [1]. The journey undertaken to market wine in both bottle and bulk may be many thousands of miles, from the New World to the Old or vice versa, or from the West to the East. This massive rise in exports has only been possible because of the considerable improvements in the technical quality and particularly the stability of the product sold. ‘It's a great wine to drink locally but it doesn't travel’, an often heard expression when visiting wine regions in the 1970s and 1980s, is but a distant memory today. Microfiltration and ultrafiltration using membrane technology have been important tools in ensuring clarity and...

Table of contents

• Cover
• Table of Contents
• Title Page
• Copyright
• Dedication
• Acknowledgements
• Preface
• Introduction
• 1 Faults, Flaws, Off‐Flavours, Taints, and Undesirable Compounds
• 2 Wine Tasting
• 3 Chloroanisoles, Bromoanisoles, and Halophenols
• 4 Brettanomyces(Dekkera) and Ethyl Phenols
• 5 Oxidation, Premox, and Excessive Acetaldehyde
• 6 Excessive Sulfur Dioxide, Volatile Sulfur Compounds, and Reduced Aromas
• 7 Excessive Volatile Acidity and Ethyl Acetate
• 8 Atypical Ageing (ATA) – Sometimes Called Untypical Ageing (UTA)
• 9 Fermentation in Bottle
• 10 Hazes
• 11 Lactic Acid Bacteria‐Related Faults
• 12 Smoke Taint and Other Airborne Contaminations
• 13 Ladybeetle and Brown Marmorated Stink Bug Taints
• 14 Sundry Faults, Contaminants, Including Undesirable Compounds from a Health Perspective and Flaws Due to Poor Balance
• 15 TDN and Tartrate Crystals: Faults or Not?
• 16 Must Correction, Wine Correction, and Alcohol Reduction Using Membrane Technologies
• 17 The Impact of Container and Closure Upon Wine Faults
• 18 Best Practice for Fault and Flaw Prevention
• Appendix A Levels of Free SO2 Required to Give 0.5, 0.625, and 0.8 mg/l of Molecular SO2 for Differing Wine pH Values
• Further Reading
• Glossary
• Useful Websites
• Index
• End User License Agreement