Understanding Wine Chemistry

Andrew L. Waterhouse, Gavin L. Sacks, David W. Jeffery

• Publisher: Wiley
• Year: 2016
• ISBN:
  9781118730706
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Analytic Chemistry

Wine chemistry inspires and challenges with its complexity, and while this is intriguing, it can also be a barrier to further understanding. The topic is demystified in Understanding Wine Chemistry, Special Mention awardee in the 2018 OIV awards, which explains the important chemistry of wine at the level of university education, and provides an accessible reference text for scientists and scientifically trained winemakers alike.

Understanding Wine Chemistry:

• Summarizes the compounds found in wine, their basic chemical properties and their contribution to wine stability and sensory properties
• Focuses on chemical and biochemical reaction mechanisms that are critical to wine production processes such as fermentation, aging, physiochemical separations and additions
• Includes case studies showing how chemistry can be harnessed to enhance wine color, aroma, flavor, balance, stability and quality.

This descriptive text provides an overview of wine components and explains the key chemical reactions they undergo, such as those controlling the transformation of grape components, those that arise during fermentation, and the evolution of wine flavor and color. The book aims to guide the reader, who perhaps only has a basic knowledge of chemistry, to rationally explain or predict the outcomes of chemical reactions that contribute to the diversity observed among wines. This will help students, winemakers and other interested individuals to anticipate the effects of wine treatments and processes, or interpret experimental results based on an understanding of the major chemical reactions that can occur in wine.

Part B
Chemistry of Wine Production Processes

19
Outline of Wine Production

19.1 Introduction

Wine production (winemaking) encompasses the techniques and technologies used in the transformation of grapes into wines of a target style, of which there are many. This primarily involves vinification (alcoholic fermentation) – the conversion of grape sugars into alcohol by yeast – but is accompanied by a variety of other important changes due to extraction and microbial metabolism of a multitude of other grape components. A secondary, malolactic fermentation (MLF), which can occur simultaneously with primary fermentation or sequentially, is also promoted for some wine styles. Furthermore, production techniques differ depending on whether white or red grapes are used and the type of wine being produced (Table 19.1).

Table 19.1 Classification of major wine styles found throughout the world. Adapted from Reference [1]

Description		Color	Residual sugar (g/L)	Alcohol (% v/v)	Examples
White wines
Still	Dry	Pale straw to gold	<9	8 to 14.5	Riesling, Chardonnay, Semillon, Sauvignon Blanc, Colombard, Grüner Veltliner, Trebbiano, Chenin Blanc
	Sweet	Light yellow to gold	9 to 30 (semi‐sweet)		Riesling, Gerwurztraminer, Semillon
			30 to 200 (sweet)		Riesling, Ice wines, Sauternes, Tokay
Sparkling	Dry to semi‐sweet	Pale straw to amber (pink to light red for rosé wines)	0 to 50		Champagne, Chardonnay/Pinot Noir/Pinot Meunier^a, Riesling, Sauvignon Blanc, Cava, Prosecco
Fortified	Dry	Pale straw to amber	0 to 30	15 to 20.5	Fino and Amontillado Sherries
	Sweet		100 to 300		Oloroso and Pedro Ximénez^b Sherries, Topaque
Red wines
Still	Dry	Dark red to red/brown	<7.5	8 to 14.5	Grenache, Merlot, Cabernet Sauvignon, Tempranillo, Zinfandel, Sangiovese, Malbec, Pinot Noir, Shiraz
Sparkling	Semi‐sweet		7.5 to 30		Pinot Noir, Shiraz, Cabernet Sauvignon
Fortified	Sweet	Red/gold to deep brown	100 to 300	18 to 22	Ruby, Tawny and Vintage Ports, Brown Muscat

^a Of these classic Champagne grape varieties, the first two tend to be used more frequently in sparkling wines.

^b Pedro Ximénez (PX) can be very sweet and may contain up to 450 g/L of residual sugar.

Certain specialty wine styles with unique production steps exist. Notably, sparkling wine involves a secondary alcoholic fermentation stage, or the addition of CO₂ under pressure, to introduce the carbonation (fizz) associated with this category of wine. Other common specialty wines are the fortified wines, which have grape‐derived ethanol added either during the primary fermentation phase (which arrests fermentation) or once dry, thereby enhancing the final alcohol content.

Finally, winemaking does not end after fermentation – a range of operations are used to clarify, stabilize, mature, age, and package the wine. This chapter offers an overview of wine production and links to later chapters, which detail the processes and chemical changes that occur at various stages during winemaking.

19.2 Basic workflow

The basic steps for winemaking are outlined in Figures 19.1 and 19.2 for white and red wines. The fundamental differences between the typical production of white and red wines can be briefly summarized as follows:

• White grapes are crushed/destemmed and pressed to juice and do not typically spend much time in contact with grape solids (i.e., there is no maceration step).
• Red grapes are crushed/destemmed and the must (juice and grape solids) undergoes maceration and fermentation in the presence of skins, seeds and juice (Chapter 21).
• As a result of the above, extraction of polyphenols is mostly avoided with white wines and encouraged in red wine production.
• Cooler temperatures are used for white fermentations to control aroma characteristics and warmer temperatures enhance extraction of solids in reds.
• White fermentations mostly exclude oxygen, whereas some aeration is encouraged during red winemaking through the maceration techniques employed.
• The majority of red wines undergo malolactic fermentation (MLF) and incorporation of oak in contrast to white wines, where only certain styles experience these treatments.
• Red wines undergo a period of maturation in tanks or oak barrels to promote stabilization of color and modification of mouthfeel.
• White wines can be released much earlie...