Grapes

Glen Creasy, Leroy Creasy

• Publisher: CAB International
• Year: 2018
• ISBN:
  9781786391384
• Edition: 2
• Topic: Biowissenschaften
• Subtopic: Gartenbau

""'Creasy and Creasy is the 'go to' reference on my bookshelf when I am searching for thoughts on current production systems. Given the authors' experience, there is good awareness of viticultural practices in different climate zones... I trust readers will find as much benefit and enjoyment with this updated volume as I found with the first."'Dr. Richard Smart, 'the flying vine-doctor', Cornwall, UKFully revised with new content and full-colour figures throughout, the second edition of this successful book contains expanded content for all sections, particularly those covering the impact of climate change, seasonal management, mechanisation and organic management options. There is a new vine balance section, as well as significant updates to rootstocks and grafting. It includes information on wine grapes in addition to grapes for fresh consumption and raisin production.Covering a broad range of topics from grapevine growth and fruit development, to vineyard establishment, mechanisation and postharvest processing, this book provides historical and current information about the grape industry and sets out the theory and science behind production practices. It is an invaluable resource for grape producers, horticulture and plant science students, as well as enthusiasts of the vine and its products.

1

HISTORY, USES AND PRODUCTION

The grapevine (Vitis spp.) is cultivated all over the world and the grape itself is used for a myriad of products, many of which are well known to all of us. Viticulture is one of the major horticultural industries of the world, with the area of grapevines cultivated exceeding 7.5 million ha (OIV, 2017a). Most grapes are grown for the production of wine but, when first discovered, its appeal as fresh eating fruit was probably what attracted the first hunter-gatherers. Today the fruit is used in a wide variety of products, ranging through fresh fruit, preserves, juice, wine and raisins.

The grapevine is a vigorously growing plant and in some places is considered an invasive weed (Uva et al., 1997). Fortunately, the fact that the grape is used for a great many products means that it can be considered more of a crop plant than a weed. The fact that the grapevine is a climbing plant lends it an unusual plasticity of form. The viticulturist can manipulate it in many ways and change the manner in which it is trained, almost yearly if desired. Few perennial plants have this kind of flexibility, which forms part of its fascination as a food crop.

GEOGRAPHICAL ORIGINS OF GRAPEVINE SPECIES

Grapevines have evolved in several different areas of the world, leading to a great many different species developing. The origin of cultivation of the V. vinifera grape, now planted throughout the world, is probably in southern Caucasia, now occupied by north-west Turkey, northern Iraq, Azerbaijan and Georgia (Mullins et al., 1992). At first, grapes (V. vinifera spp. sativa) were probably gathered from the wild, with the vines growing up into the trees. The association of grapes with oak, now used in the winemaking process in the form of barrels in which wine is aged, may have begun with the vine using oak trees as support, since Saccharomyces cerevisiae (or the winemaking yeast) strains have been isolated from oak trees (Sniegowski et al., 2002). The people living in these areas in ancient times discovered the utility of V. vinifera grapes and took the vine with them on their trading routes, to Palestine, Syria, Egypt, Mesopotamia and then to the Mediterranean. The Greeks, Phoenicians and Romans (Buxó, 2008) took to the vine readily and spread it, and methods for its cultivation, throughout Europe and as far north as Britain.

From Europe, V. vinifera was taken to North America, Peru and Chile, with the Dutch ensuring it travelled with them to South Africa (1616). The English packed grapevines on the First Fleet to Australia (1788) and on travels to New Zealand.

Species of grapes native to North America are numerous, having originated in many different types of environments, from moist to dry (see Fig. 1.1). The V. labrusca grape, native to north-eastern USA, is widely used for juice production in many US states and in South America. Other species are not so commonly used for grape production, including many native to Asia, but they do make an important contribution to the production of grapes, as will be discussed later.

FAMILY, GENUS, SPECIES AND RELATED PLANTS

Botanically, the grapevine is a liana, a climbing vine. As such, it does not invest heavily in something as solid as a tree trunk for support, rather having developed to take advantage of trunks already occurring in forests and bushlands. In the wild, the grapevine starts as an understorey plant, growing rapidly and upward, clinging to other plants to eventually reach the top of their canopies (see Fig. 1.2). Once there, it fruits heavily, producing dark-coloured berries that birds, in particular, eat, thus disseminating the seed. These fruits are not very appetizing to humans, being strong in flavour, high in acidity and relatively low in sugars. In some cases, wild grapes can be palatable, such as V. amurensis, the Amur grape, which has its origin in north-eastern Asia. This species has been useful in breeding programmes due to its cold hardiness and resistance to some diseases, but it has also been used to make still table wines.

Fig. 1.1. Vitis riparia grapes growing wild in the north-east of the United States. The berries are densely coloured and strong of flavour.

Fig. 1.2. Vitis riparia smothering a tree in an upstate New York winter.

The seedling, when it sprouts, shows off two rudimentary leaves, thus indicating that it is a dicotyledon, like most broadleaved plants (and unlike monocots, e.g. maize and other grasses). The fruit is a true berry (botanically speaking), containing the seeds within, and thus the grapevine is classified as an angiosperm.

The grapevines belong to the family Vitaceae, which are mostly woody, tree-climbing vines, though a few have a shrubby growth habit. They are characterized by tendrils and inflorescences opposite the leaves. There are 12 genera within the family including Vitis, Ampelocissus, Clematicissus, Parthenocissus (Virginia creeper), Ampelopsis and Cissus (kangaroo vine).

The genus Vitis is the part of Vitaceae that the grapevine industry is most interested in and it consists of two subgenera, Vitis and Muscadinia. One peculiarity of the genus is that the flower petals separate from the bottom of the flowers, not from the top as in most other plants (see Fig. 1.3), hence it is referred to as a calyptra (ancient Greek for ‘veil’), or cap.

The subgenera are distinct because they have different chromosome numbers (38 for Vitis and 40 for Muscadinia) and morphological features. Muscadinia (V. rotundifolia), in comparison with Vitis, have differences in seed shape, simple as opposed to branched tendrils, smooth bark, continuous pith inside canes (i.e. there is no interruption at the node position), fewer berries per cluster and berries that tend to abscise from the rachis (Williams 1923; Bailey, 1933; Einset and Pratt, 1975). There are three named species in this group, the most important of which is V. rotundifolia – discussed further in Chapter 2, V. munsoniana and V. popenoei.

Fig. 1.3. Grape cluster showing individual florets, some of which have their fused petals (calyptra) separating from the basal part of the flower (top and left).

Because of their different chromosome number, plants in this subgenus will not naturally interbreed with Vitis species. However, through the use of tissue culture techniques, crosses have been made (Alleweldt and Possingham, 1988). This may be important from the standpoint of producing grapevines with enhanced disease resistance or other desirable characteristics.

Vitis includes many species, including V. vinifera, the most widely planted grape species in the world, which is used primarily for wine, table consumption, juice and raisin production.

Another well-known species is V. labrusca, native to North America. Its advantages over V. vinifera are that it is much more tolerant of pests and diseases, but for many, the flavour of the fruit, described as foxy, is an acquired taste. Hence, though they are made into wine, the grapes are mostly used for production of juice and preserves, though there is also a significant, but regional, industry producing them for fresh consumption.

Regardless of how the fruit tastes, many of the non-V. vinifera species have been vitally important to the commercial development of V. vinifera cultivars, in finding a solution to the problem of phylloxera (an insect that attacks grapevine roots) and other soil-related pests and conditions (further discussed in Chapters 5 and 9).

NATURAL GROWTH CONDITIONS

The grape is a hardy perennial plant, meaning that it can grow and survive in areas where the temperature goes well below freezing in the winter season: under the right conditions, some grape species can survive temperatures as low as -40°C (Pierquet et al., 1977) and there are active breeding programmes working to develop more cold-hardy cultivars for both table and wine purposes (such as the University of Minnesota’s ‘Frontenac’). However, V. vinifera is much more tender, and generally cannot withstand temperatures below -15°C without suffering damage (Clore et al., 1974). The above-ground parts of the vine develop a hardy outer covering called a periderm as the growing season ends, which is an indicator that the vine tissues are developing resistance to environmental extremes.

The grapevine evolved in temperate climates, so it grows when conditions are warm enough, but stops when temperatures fall below about 10°C. Unlike tree fruits, e.g. apple or pear, which set a terminal bud as winter approaches, grapevines will continue to grow as long as conditions permit.

The vine is highly adaptable to different environments which, in part, is why it is found growing in many and varied climates. Typically, at least in terms of commercial production, it is cultivated between the 10°C and 20°C annual global isotherms, although grapes are now grown in many areas outside these boundaries due to identification of suitable mesoclimates and increased knowledge about their cultivation. There would be few areas in the world that would be too hot for grapevines to grow, assuming that other plants can also survive there. However, obtaining a reliable commercial crop from those vines may be the most challenging aspect.

HISTORICAL CULTIVATION

It did not take long for people to recognize the advantages of cultivating crops rather than collecting from the wild. The Egyptians were using grapes from approximately 3000 BC, and pictures showing vines growing on structures date back to around 1500 BC (Singer et al., 1954, cited in Janick, 2002). The Chinese had probably started cultivating V. vinifera vines by 2000 BC (Huang, 2000) and native cultivars (based on V. amurensis, for example) before that. The plastic nature of the vine lends itself well to manipulation and doing so with some form of trellis exploits the vine’s tendency to fruit heavily. Early trellising systems appeared to be forms of arbours, rather than the more common hedge or overhead trellises seen today. However, there has been little commercial adoption of trellis systems that have been introduced over the past 100 years. Be that as it may, structures for supporting vines can and do take many different forms and are discussed in more detail in Chapter 6.

USES

Just as the grapevine is highly adaptable to where and how it is grown, its fruit is also highly adaptable to different uses. Somewhat unique, the grape attains a high concentration of sugar when ripe, and also (depending on cultivar) pectin, as well as a wide range of aromatic compounds. These factors, in concentration with the presence of relatively high levels of acids (particularly tartaric acid), mean that the fruit is amenable to many different end uses. Approximately 50% of global grape production is used for wine and related fermented products, with table grapes increasing in importance since 2000 to 36% of the total in 2015. Raisins make up 8%, with juice and other uses making slightly more that 5% (OIV, 2017a).

Fermented grape products

Evidence that humans were fermenting grapes with the specific purpose of making an alcoholic beverage can be traced back to around 7000 BC in China (McGovern et al., 2004), in the Near East around 6000 BC (McGovern et al., 2017). There is an association between grapes and various types of yeasts (usually living on the surface of the berry) (Parish and Carroll, 1985; Martini et al., 1996; Cavalieri et al., 2003), so it is likely, at least initially, that fruit which had been picked and stored may have started fermenting naturally. This will have produced an alcoholic mixture that some found enjoyable, and thus people wanted to be able to repeat the process. This was possibly the beginning of winemaking.

Much of the world production of grapes ends up as wine, and it is made into a bewildering array of types and price points. Wine can be thought of as a naturally made storage form of the fruit as it retains characteristics of the grape and, protected from oxidation, can remain palatable for many years. The production of wine from grapes can be simple – with few additions postharvest – to complex, with addition of a variety of substances designed to modify its appearance, aroma and taste.

Wines can be further manipulated in the form of sweetening and the addition of additional alcohol, which produces fortified wine products such as port and sherry, which were even more stable and travelled better on long sea journeys. With distillation, wine can be transformed into products such as brandy, grappa and marc, which often carry the characteristics of the grape variety from which they were made. However, the skill of the grape grower, in producing the starting material for the beverage, is still paramount in the production of a quality wine and subsequent products, such as those made through distillation.

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