A Complete Guide to Quality in Small-Scale Wine Making

John Anthony Considine, Elizabeth Frankish

• Publisher: Academic Press
• Year: 2013
• Topic: Technology & Engineering
• eBook ISBN:
  9780124079175
• Subtopic: Food Science
• Index: Technology & Engineering

As the wine industry has experienced a period of rapid global expansion, there is a renewed emphasis on quality and consistency even within the small winery industry. Written for the small production program, A Complete Guide to Quality in Small-Scale Wine Making is for the novice to intermediate level winemaker seeking foundational information in chemistry and sensory science as they relate to wine quality at a technical level. Drawing from personal experience as well as scientific literature, this book introduces the core concepts of winemaking before delving into methods and analysis to provide practical insights into creating and maintaining quality in the wine product. - Understand the chemistry and sensory science at the foundation of quality wines - Explore real-world examples of key analysis and application of concepts - Practice methods and exercises for hands-on experience

Chapter 1

Introduction to the Table Wine-Making Process

Common and distinguishing aspects of the production of red and white wines are explained with the purpose of giving the reader a framework on which to add the details. Aspects considered are the workflow from vineyard to palate and concepts of quality and its assessment in grapes and in wine. The role of chemical and physical methods in making those assessments is explained and placed in context with biological, human, judgment. Yeast and bacterial primary and secondary fermentations are introduced, as is the role of hygiene in minimizing the risk of microbial faults from yeasts or bacteria. Yeast nutrition in relation to grape vine nutrition is introduced along with the vital role of organic acids and sulfur in aiding hygiene and controlling cultured and wild organisms during and after fermentation. Emphasis is placed on developing personal sensory skills as a key element on quality control throughout the process.

Keywords

grape quality; history; process; production; quality; wine

Chapter Outline

1. Introduction

2. Great Wines Begin with Great Grapes

2.1 Measuring Quality

2.2 Measuring Maturity

2.3 Tasting Grapes

2.4 Postharvest Quality

3. An Overview of Key Elements in Wine Making

3.1 Fermentation

3.2 Composition Parameters

3.3 Ammonium and Amino Acids

3.4 Sulfur

1 Introduction

Wine making is a blend of ‘art’ and of ‘science’. It is complex and enduringly intellectually challenging. The endeavor of producing a truly fine wine, in successive years, from fruit that differs from one year to the next is a never-ending source of motivation and pleasure; how can the winemaker add value to this fruit? This book aims to guide the aspiring winemaker in the production of a technically sound wine. The challenge to you, the winemaker, is to go from that base to producing ‘fine’ wines consistently, and perhaps even exceptional wines.

Wines of all styles have a great deal in common, but producing a specific wine style may demand unique conditions. Broadly speaking, ‘red’ wines are exposed to oxygen during the primary ferment while ‘white’ wines are not (Figure 1.1). Red wine fermentation is carried out at a higher temperature (25–30°C) to aid extraction of tannins and color while white wines are fermented at 15–20°C to preserve volatile aromas. Red wine ferments include all berry parts, skin, pulp and seeds, but white wine ferments include the juice or ‘must’ pressed from the pulp only in order to minimize the extraction of bitter phenolics and tannins.

Figure 1.1 Outline of the wine-making process for red and white wines illustrating the flow of the processes and their distinguishing features.
Note especially the regions that are fully aerobic, microaerobic and anaerobic. In red wine production, the anaerobic region may be managed microaerobically through a process known as microoxidation.

Red wines are double fermented: first with a yeast to process sugar to alcohol, and then with a bacterium to convert malic acid to lactic acid. The latter process reduces acidity, adds flavors that enhance red wines, especially in conjunction with oak, and helps to ensure stability against secondary fermentation in the bottle, even if the wine is not fully sterile.

White wines, with some exceptions such as Chardonnay, are yeast fermented only, then chilled and stabilized. Very careful filtration is required to remove all microorganisms to prevent fermentation of malic acid once bottled. This is a much quicker process and one that generally suits the dry, crisp, aromatic palate generally sought in such wines.

Elements common to both processes include hygiene, the fermentation of grape sugars, management of acidity and nutrient status, and certain steps to protect and stabilize the wine. The distinctions between the two processes are vital, however. It is possible to produce an acceptable red wine in your ‘backyard’ but challenging to produce a sound white wine under such circumstances. This is because of the much greater control that is required of oxygen status, hygiene, yeast nutrition and temperature.

Typically, a commercial yeast culture is added at the beginning to red and white crushed berries or musts. Wild yeasts that are present on the surface of grapes may do the job and may produce exceptional wine, but, then again, may result in an undrinkable wine. Few wild yeast taxa are able to complete fermentation to dryness, that is, to ferment all the available sugar. Unfermented sugar, termed residual sugar, impairs not only the palate of a wine but also its stability subsequently against in-bottle fermentation and contamination by spoilage microorganisms. Only commercial yeast genera (Saccharomyces) can complete fermentation reliably. These yeasts also occur naturally but are rare in the vineyard (however, they are common in a winery).

Sulfur dioxide (SO₂) is added at harvest, usually, or at crushing, to reduce the risk of oxidation and to suppress wild yeasts and bacteria that may spoil the wine. SO₂ is an essential part of modern wine-making practice. Its addition is especially important once fermentation has finished in order to reduce the risk of oxidation and spoilage. It is usually added as the salt, potassium metabisulfite (K₂S₂O₅), although it may be applied as a gas (SO₂).

Red wine making is an ‘extractive’ process that is carried out in the presence of the skins, seeds and possibly even some stems (Figure 1.1). It is less prone to oxidation because of the presence of high levels of antioxidants: tannins and anthocyanins. Indeed, some mild oxidation may be beneficial: it is part of the process. The skins, which naturally float and form a ‘cap’, are buoyed by carbon dioxide (CO₂) produced during fermentation. The cap is mixed with the must regularly (plunged or bathed by pumping the liquid over the top) to encourage the extraction of anthocyanins and tannins. Failure to do this will lead to the growth of spoilage yeasts on the surface. For a review of red wine-making processes see Sacchi et al. (2005).

Red wines and some white wines undergo a secondary fermentation that is accomplished by a bacterium, Lactobacillus oeni. This is termed a malolactic fermentation. It reduces wine acidity by converting malic acid to lactic acid. This may be especially important in wines produced from grapes grown in a cool climate and which may have a high level of malic acid at harvest. It also increases stability against spoilage and fermentation in-bottle by removing a remaining fermentable substance, malic acid. The bacterial fermentation may also broaden the spectrum of aromas and flavors. In large commercial wineries this fermentation is conducted in tanks but for premium wine and in small wineries it is often performed in small oak barrels.

White wine is sensitive to oxidation, especially after fermentation, is not extractive and must be stabilized by sterile filtration (Figure 1.1). Part of the stabilization process for white wine involves chilling before bottling to precipitate excess potassium bitartrate salts (as used in baking powder), which might otherwise form unsightly crystalline deposits in the bottle when refrigerated. White wines are also ‘fined’ with a clay (bentonite) to remove excess protein that might coagulate and form an unsightly haze should the wine get too hot during storage and transportation. Finally, they may be treated with copper sulfate to remove hydrogen sulfide (H₂S) ‘rotten egg’ gas that may be formed when starving yeast metabolize grape proteins (this may also be true of red wines but they usually contain more nutrients). Other fining processes to remove bitter tannins may include the use of natural products such as proteins from eggs, fish or gelatin, or synthetic products such as polyvinylpolypropylene (PVPP). These precipitate and are removed before bottling.

Aging in ‘toasted’ oak is a standard practice in the art of red wine making to broaden and balance the sensory characters of the final wine. Selection of particular oak sources and of the level of toast is a major part of fine wine making and an expensive aspect. Oak may also be used with some white wines (e.g. Chardonnay) and some Sauvignon blanc and Semillon wine styles (e.g. Fumé blanc).

The processes are simple conceptually. The art lies, however, in the science of analyzing the raw ingredients, in monitoring the process, and in the skill and judgment of the winemaker in managing the details of the process. Vital also are the skills of the viticulturist in matching cultivar to site and in devising appropriate vineyard management strategies—as well as luck in the season.

The final product is judged on its sensory appeal, and being aware of this throughout the process is at the heart of becoming a good winemaker. Once a wine becomes spoiled its value is limited or nil. The chemical and the quality assurance processes described in this text serve to assist in that goal, but do not guarantee it. Sensory alertness to ‘off’ flavors and aromas in vessels, pumps, tubing, etc., is vitally important as the human nose can detect some aromas down to picogram or even femtogram levels (10⁻¹² to 10⁻¹⁵ g/L). As in all things, prevention is far better than cure: be alert and avoid problems. Care needs to be taken, however, to check one’s palate outside the winery, for it is easy to become adapted to particular off-aromas (e.g. Brettanomyces is a problem requiring constant management in even the best of commercial-scale wineries).

2 Great Wines Begin with Great Grapes

Quality is an issue that may make or break the smaller vineyard owner and determine the profitability of even the largest vineyard company. This is the case because the value of the fruit depends on the winemaker’s judgment (and experience) regarding the value of the wine that may be made from that fruit. Fruit destined for super-premium wine may be valued at two- to 10-fold dollars per tonne above that for standard commercial fruit.

Defining grape quality and selecting appropriate maturity indices and quality measures are issues that are still widely debated among viticulturists and winemakers. Commonly, fine wines are associated with regions that inherently produce low vigor and low yields in a climate that enables full ripening under mild climatic conditions (Gladstones, 1992; Jones et al., 2010; White et al., 2006).

The best indicator of potential quality is history. This is the basis on which regional quality assurance labels are allocated, e.g. the Grand and Premier Cru classifications in France. Experience tends to be the benchmark on which site selection is determined. For example, the premium viticultural areas of the ‘New World’ in southern Western Australia were identified by comparison with the best viticultural regions in France and California. These regions had a long and relia...

Table of contents

• Cover image
• Title page
• Table of Contents
• Front-matter
• Copyright
• Acknowledgements
• Preface
• Chapter 1. Introduction to the Table Wine-Making Process
• Chapter 2. Flavors and Aromas in Foods and Beverages
• Chapter 3. Wine Chemistry
• Chapter 4. Safety
• Chapter 5. Table Wine Production
• Chapter 6. Microbiology and Methods
• Chapter 7. Harvest Protocols
• Chapter 8. Winery Protocols
• Chapter 9. Principles of Analysis
• Chapter 10. Essential Analyses
• Chapter 11. Quality Assurance, Teaching and Research
• Chapter 12. Sample Statistics
• Bibliography
• Appendix. List of Abbreviations and Symbols
• Index