How does the grape get from the vineyard to the bottle on the shelf? How does soil affect wine quality? What exactly does oak do?
In this section you will find all you need to know about Vitis Vinifera and how it produces the grapes that eventually become the wine in your glass. From soil to climate, fermentation to bottling, the following pages are an introduction to the complex business of making wine
Written by Jonathan Pedley
Winemaking – the vine
There are over a thousand different varieties of ‘Vitis vinifera’ (the vine used for wine production) all over the world. The grapes range from the modern types,generated by crossing pre-existing varieties, to the more traditional ones suchas Pinot Noir and Riesling
It is this vine which has been used to make wine down the millennia in the Middle East and Europe, and which nowadays is planted in the New World as well. There are over a thousand different varieties of Vitis vinifera. Each of these varieties produces wines with an individual flavour – many of these such as Chardonnay and Cabernet Sauvignon, have become household names.
Most of the familiar ones, like Pinot Noir and Riesling, have been with us for several hundred years. However, many ‘new’ grape varieties, such as Muller-Thurgau and Pinotage, have been generated in modern times by crossing pre-existing varieties.
Vitis vinifera’s greatest weakness is its susceptibility to an aphid called Phylloxera vastatrix. This vine louse was introduced from Californian vines and spread rapidly throughout most of the world’s vineyards during the second half of the nineteenth century. Phylloxera destroys the root system of the Vitis vinifera, ultimately killing it. There were no effective treatments.
Fortunately, it was noticed that some of the vine species originating in North America, such as Vitis rupestris and Vitis riparia, could cope with Phylloxera. These vines did not produce attractive wines, but by grafting a cutting of Vitis vinifera onto an American vine rootstock, growers were able to replant their devastated vineyards.
Most of the world’s vineyards are planted with grafted vines like this today, everything above ground being Vitis vinifera, and everything below ground being American vine. The main exceptions are vineyard areas like Chile and South Australia, that have to date avoided Phylloxera infestation. In these cases Vitis vinifera vines can still be planted on their own roots.
It takes a newly planted vine three of four years to produce its first crop of grapes. Once in cropping mode, young, vigorous vines yield quite heavily. The quality of the fruit at this stage is often a little simple. As the vine gets older, over thirty years or so, its vigour declines and yield drops. However, what fruit it does produce becomes increasingly concentrated and intensely flavoured. It should come as no surprise that many of the world’s most interesting wines are made from the fruit of old vines.
Winemaking – the soil
Everyone agrees on a few basics. Vineyard soils need to drain well. Equally, if irrigation is not an option, the soil needs to be able to retain some moisture to see the vine through the summer. Furthermore, the vine needs to draw certain key nutrients, like iron and nitrogen, from the soil.
So far, so good. It is what comes next that has exercised the great wine minds of the last few hundred years. The empirical observation over the centuries in Europe, and particularly in France, is that certain vineyard plots pretty consistently produce wine with a distinctive discrete character. Somewhere like Burgundy, a grower may own two neighbouring plots of land, which he cultivates in exactly the same way, and yet the wines from these two sites taste different.
Why? The vine’s environment is thought to be responsible in some way. The French word ‘terroir’ encapsulates elements like the soil, the slope and the localised climate, which make no two places identical in terms of environment. By extension therefore, no two wines from different vineyards will ever taste quite the same.
Although the cultural gap is probably less now than it was in the past, it is possible to say that a French wine’s terroir is still seen as the most significant determinant of its style and quality. By contrast, many growers in the New World, whilst recognising the role of soil, aspect and ‘microclimate’, would not accord terroir alone the semi-mystical significance it has in parts of Europe.
The soils which are a component of the best terroirs in France are often low in organic matter and quite poor. The vigour and yield of the vines is thus naturally restricted. This leads to another much-argued observation which is that most great wines are made from low yielding vines.
Winemaking – the climate
Most of the world’s vineyards are planted in the temperate latitude zones of 30-50 degrees North and 30-50 degrees South. Within these zones the actual climate has a huge influence on the type of wine produced.
In a cool country like Germany, the grapes will ripen slowly. Even if they are not picked until the end of October, they will retain high levels of acidity. Much of this acid goes right through the winemaking and ends up in the finished wine. Not good if you have an ulcer, but crucial to the balance of most great white wines.
Conversely, the build-up of sugar will be very slow. Without much sugar in the grapes, the resulting wine will be relatively light in alcohol. Of course a hot climate will have the opposite effect, usually giving wines with a hefty blast of alcohol and soft acidity.
Like most plants, vines need a decent amount of water to survive and flourish. Historically it made sense to plant vineyards in places where the climate delivers a reliable annual rainfall. Think of the Atlantic dominated climate of Western Europe. With irrigation it is possible to plant vines in some pretty arid places, such as the Central Valley in Chile, the Riverland in Australia, and Washington state – where about the only naturally-occurring vegetation is sagebrush.
With the rise in the temperature the buds will burst and growth starts. This spurt of spring growth produces a profusion of shoots and leaves. Warmth and some rain will help to keep this vigorous growing phase on track.
The grower has to be vigilant for the first sign of any pests and diseases, and apply the appropriate sprays or biological controls. At the end of the spring period the vines flower.
Assuming the flowering was successful, a crop of grapes will set. Dry, warm and sunny weather is then required to swell and ripen those grapes. The vines may need to be trimmed to keep the vineyard neat and to allow good sun exposure and air circulation. This technique is also used to keep the yield down. If the crop looks like being excessive some properties will cut away some of the immature bunches. Spraying against pests and diseases continues. In the early part of the summer all the grapes are green in colour. Towards the end of summer the colour forms in the skin of the black grapes, a process called ‘veraison’.
A final period of fine weather is needed to complete the ripening of the grapes and to harvest them. Some grape picking is still done by hand. Whilst this is obviously labour intensive and very costly, it does allow the grapes to be sorted carefully at the vineyard or winery. Machine picking is much quicker and cheaper, but it does not allow the same rigorous grape sorting. That said, machine picking can be particularly advantageous in hot climates as it allows harvesting in the cool of night. However they’re picked, the grapes need to be transported from the vineyard to the winery as quickly as possible. A few weeks after picking the vines will lose their leaves, and they then shut down for the winter dormancy.
During the winter months the vine is dormant. A period of frost and snow is actually beneficial, helping to kill off over-wintering pests and diseases. Heavy rain is also welcomed as it allows the soil to replenish its water reserves. A lot of general maintenance takes place in the vineyard, with trellises repaired and fertilisers applied. The main winter chore for the grower is to prune the vines. There are a number of vine pruning and training systems in use today. The Guyot system which is used extensively in France involves pruning the vine back to just on or two canes, and then training these along wires. The more old-fashioned bush training system has no wires, the vines being pruned back to an unsupported gnarled trunk. This ancient technique can still be seen in several Mediterranean countries, as well as in a number of the oldest vineyards in Australia and California.
Winemaking – what can go wrong
Either through their geological composition, or through continuous cultivation, some soils become deficient in key nutrients. After soil analysis, this can be solved by adding chemical fertilisers. However, the trend at present is to return to more natural treatments like compost and manure. This is all part of the move by some growers towards ‘organic viticulture’.
Winter frost – temperatures below -16 degrees will freeze the vines and kill them. The main advice to grape growers is don’t plant your vines in areas where this sort of frost is a regular occurrence.
Spring frost – once the buds have opened, it only needs the temperature to dip to zero degrees for the new growth to be damaged. The vines are not killed, but the loss of the embryonic flowers can drastically reduce the current year’s crop. Heaters, fans and water sprays can be used to limit the damage.
Poor weather at flowering – extremes of temperature and rain can severely disrupt the flowering. The knock-on effect is that the grower ends up with a smaller crop than normal.
Hail – although often very localised, a hail storm can bruise and batter the vine. Damaged grapes can very quickly succumb to grey rot. Firing rockets into the clouds can precipitate the water as rain rather than as ice.
Drought – where irrigation is not an option, summer drought can actually cause the grapes to stop ripening.
Rain at harvest – a year’s toil can be compromised by a couple of days rain just before the harvest. The water causes dilution and the extra humidity can trigger grey rot.
The most significant pest of the vine is Phylloxera vastatrix. Other invertebrate pests include various mites and caterpillars. Many of these are controlled with pesticides. Baboons, kangaroos, rabbits, birds and deer all damage vines by eating leaves, fruit and nibbling bark.
Mildew – Two versions of mildew, downy and powdery, attack the green parts of the vine. The leaves and fruit are damaged, and ultimately the crop is ruined. Mildew can be prevented by a regular spraying programme.
Rot – Caused by a mould called Botrytis cinerea, the destructive ‘grey rot’ attacks the grape bunches and destroys them. However, in certain circumstances, rather than ruining the grapes, the Botrytis mould can cause ‘noble rot’. In this case, the grapes shrivel up, concentrating sugar, acid and flavour. These hand picked ‘noble rot’ grapes are used to make many of the world’s great sweet white wines (e.g. Trockenbeerenauslese and Sauternes
Winemaking – What’s in a grape?
Sugar – the yeast needs to get at this to convert it into alcohol and carbon dioxide.
Acids – there are two main acids in grapes, tartaric and malic. There is usually more tartaric acid than malic acid. Much of the tartaric acid gets right through the winemaking process, and gives the finished wine its freshness. After alcoholic fermentation a controlled process known as malolactic fermentation takes place during which tart-tasting malic acid is converted to softer lactic acid. The longer and more complete the malolactic fermentation, the softer and rounder the wine. Winemakers typically suppress the malolactic fermentation with sulphur dioxide if a more acidic, fresher-tasting wine is desired.
Water – it is the water from the pulp of the grape that we actually drink. Unlike in brewing, for example, no added water is needed in the winemaking process.
Grape pips contain bitter oils. For this reason, whatever is done in winemaking it is important to avoid crushing the pips.
The stalk contains woody tannins. Some winemakers still include the stalks in their fermentations to extract these tannins, as well as the tannins from the skins. However, the more normal practice nowadays is to de-stalk the grapes when they arrive at the winery.
Colour – the colour compounds, anthocyanins, are located in the skin of the black grapes. The anthocyanins need to be extracted from the skins to get the colour in red wines. By contrast, if the juice can be squeezed from the pulp with little skin contact, then white wine can be made from black grapes. Many of the great champagnes are made from a blend of Pinot Noir, Pinot Meunier (both black) and Chardonnay.
Tannins – these are the dry, astringent tasting compounds that are usually extracted from the grape skins at the same time as the colour. They are one of the elements which give some red wines their longevity.
Flavour – Many of the natural flavouring compounds occur in the grape skin or just below it.
Bloom – the greyish, waxy layer on the outside of the grape skin is called the ‘bloom’. Naturally occurring wild yeasts are found in the bloom.
Winemaking – into the winery
On arrival at the winery the grapes will be crushed and
de-stalked. Pressing then follows to release the juice. The gentler the
pressing, the finer the juice. The juice (also called ‘must’) is allowed to
settle for a few hours. Any adjustments to the must can be done at this stage,
including the addition of extra sugar (‘chaptalisation’). A little sulphur
dioxide, the main preservative used in winemaking, is usually added as well.
It is normal nowadays to add a yeast culture to the must to start the
fermentation. The yeast attack the sugar and convert it into alcohol and carbon
dioxide. Most white wines are fermented at a low temperature between 15 and 20
degrees to retain freshness. It takes about two weeks for all the sugar to be
converted, leaving you with a dry white wine. Most fermentations now take place
in stainless steel vats, although some of the smarter white wines are fermented
in small oak barrels.
Once the fermentation has finished the yeast sinks
to the bottom of the vat and forms a sediment (the ‘lees’). Whilst resting on
the lees wine can undergo a second transformation called ‘malolactic
fermentation’. In this process bacteria attack the malic acid (which has a sour,
green taste) and convert it into lactic acid (which is softer and more buttery).
Winemakers can now decide whether to encourage or block this transformation.
The wine will then be drained out of the vat leaving the lees behind (a
process called ‘racking’). Most white wines will then be matured for a short
period, usually around six months or so. If this period is spent in oak barrels,
the wine will pick up some of the distinctive oak flavours. By contrast, if this
time is spent in stainless steel, the wine will retain its pure fruit character.
On arrival at the winery the black grapes are crushed and
de-stalked, but are then pumped direct to the fermentation vats. The essence of
red winemaking is that the must will ferment in contact with the skins, from
which colour and tannin are extracted. Any additions of sugar, sulphur dioxide
or yeast can be made directly to the fermentation vat. To assist in the
extraction of colour, most red wines are fermented relatively warm(25-32
degrees). It is also usual to mix the skins and must together as much as
possible during the fermentation.
Once the fermentation has finished
most of the red wine can be drained off through gravity. This component is
called ‘free run’ red wine. The skins and pips are then removed from the vat and
pressed to release the ‘press wine’. The latter can sometimes be excessively
harsh and tannic, but on other occasions it can be blended with the free run
wine to improve its body.
All red wines undergo malolactic fermentation
to soften them, before racking and maturation. Red wine is usually matured
longer than white – around 18 months or more. As with white wine, the use of oak
barrels (particularly if they are new) will have a significant effect on the
wine’s character. Because the red wines spend so long in wood, it is normal to
rack them every three months or so to remove any sediment that has accumulated.
Of course it is possible to make rose just by mixing red and white wine, but this is not the usual approach. The normal
technique is to take black grapes, crush them, and allow the juice to stay in
contact with the skins for a few hours. The juice will pick up some pink colour
from the skins, and once this is achieved, the juice is drained off the skins.
From then on the production of a rose follows the white wine process, with a
cool fermentation and a short period of maturation.
Only sparkling wine from Champagne can be called
Champagne. All other sparkling wines must be labelled as such. Various
techniques exist for making sparkling wine.
The traditional method
involves taking a base wine and putting it through a second fermentation in
bottle. The carbon dioxide produced during the second fermentation cannot escape
from the bottle and so the wine turns fizzy. The traditional method is the most
expensive and time-consuming, and is used for all the great Champagnes. Other
sparkling wines such as Cava (Spain) use it, and label their bottles accordingly
– ‘Traditional Method’.
The tank method also involves a second
fermentation, but in this case it takes place in a large vat, rather than in an
individual bottle (e.g. Vin Mousseux and most Sekt).
Carbonation or the
bicycle pump method involves taking a base wine and injecting carbon dioxide.
This is the cheapest method – also used for fizzy canned drinks. The bubbles are
large and disappear quickly.
exist for making sweet wine. If a winemaker is lucky enough to have grapes with
noble rot, then these berries contain so much sugar that the yeast cannot
ferment it all, leaving some residual sweetness (e.g. Sauternes). A dry wine can
be sweetened by adding unfermented grape must (e.g. Liebfraumilch). Note: It is
usually illegal to sweeten a wine just by adding sugar. The fermentation can be
arrested either by refrigeration (e.g. Asti) or by the addition of brandy (e.g.
Fortified wines tend to have complex
production processes which differ markedly from each other. However, brandy
(also known as ‘grape spirit’) is added during their production. With Sherry the
spirit goes in after the fermentation, whereas with Port it goes in during the
Winemaking – cleaning up and bottling
At the end of the maturation period the wine needs to be cleaned up in preparation for bottling. There are a number of techniques that can be used to stabilise and clarify wine:
Fining – this is done by adding a fining agent to the wine which causes the lees to fall to the bottom from where they can be racked off. The main fining agent for white wine is a clay called Bentonite. Red wines are traditionally fined with beaten egg white, or other protein rich substances like gelatin.
Centrifugation – by spinning a wine at high speed yeast and bacteria can be removed from a wine. Cold treatment (or ‘tartrate stabilisation’). Many white wines are held at -3 degrees for a week just before bottling. This cold treatment precipitates out any excess tartaric acid in the form of tartrate crystals, hopefully preventing a crystal deposit forming in the bottle later.Filtration – this is the process used to remove any remaining yeast or bacteria from a wine. There are three main types of filter:
1. Kieselguhr (or ‘diatomaceous earth’) – to a layman it looks as if the wine is being filtered through mud. Used as the first stage in cleaning up a wine containing lots of yeast.
2. Cellulose (or ‘plate and frame’) – these filter pads look like thick pieces of white cardboard. Effective in removing most remaining yeast. 3. Membrane (or ‘sterile’) – made of synthetic polymers, a membrane filter will remove all remaining yeast or bacteria.
Pasteurisation – heat treating a wine just before or during bottling is still occasionally used to be sure that there are no active microbes present. However, the damage caused to wine by flash pasteurisation, coupled with the availability of membrane filters, has seen a decline in the use of pasteurisation in wine production. Hence most wines nowadays are ‘cold sterile bottled’.
If all or most of the above techniques are used on a wine it will almost definitely be clear and stable when bottled. However, each of these manipulations inevitably strips some flavour and character from a wine. There is an ongoing debate in the wine industry as to how much a winemaker should or shouldn’t do to his wine to reconcile the need for stability on the one hand, with flavour and character on the other.
Modern wine bottling lines are clean, highly automated facilities. Hygiene and sterility are priorities to try and ensure that the risks of contamination and oxidation are minimised. Various techniques exist to ensure that the bottles themselves are clean, and that the wine does not suffer too much air contact during the filling itself. The big debate at the moment concerns the use of natural cork to close the bottle. Natural cork is a tried and tested material, but it is increasingly expensive, and can spoil a wine through cork taint or by allowing air into the bottle. The use of synthetic cork is on the rise, whilst others advocate the use of screw tops or beer bottle tops for day-to-day wines.