The growth cycle.
Over the winter period (Northern hemisphere December, January, February and Southern hemisphere June, July, August) the vine is dormant, this period is extremely important and although no fruit production occurs it is when the vine rests. Without this dormant time the vine could overproduce and the quality would be much lower. During this period pruning will also occur deciding the shape of the vine for the following year.
Bud burst is the next stage, this is the location on the vine that will produce the all important grapes. The buds will then open into flowers. Flowering is extremely important, each flower has the potential to become one grape depending on whether pollination occurs or if environmental damage destroys the delicate flowers.
Fruit set then occurs. Here the flowers become small green berries and their main role is to protect the grape seeds. Then ‘verasion’ occurs, this French term refers to the point at which the grapes begin to ripen. During ripening the sugar levels increase, the skin colour begins to develop and grape size will also increase. In the time from bud burst to the grapes becoming fully ripe the grower can decide to remove bunches of grapes or leaves in order to limit yield and produce more concentrated flavours. Removing leaves limits the amount of photosynthesis that can occur in the plant.
Finally harvesting will begin. At this stage the grapes are fully ripe, care must be taken to pick at the right time, too early and the flavours and sugar will not have fully developed, too late and the levels of acidity will have decreased.
Unlike weather, climate refers to the general patterns of the region and will not drastically change year upon year. There are three main climates associated with grape growing; Continental, Maritime and Mediterranean. Within these categories there are two important factors that must be understood in order to appreciate the differences between the styles of climate.
Continentality, this is a measure of the difference between the coldest and warmest temperatures, usually between winter and summer months. A high continentality will mean a large difference between the temperatures.
Diurnal range, this is a measure of the difference between daytime and nighttime temperatures. The higher the diurnal range the larger the difference between the two temperatures.
Continentality is important in grape growing as it allows the vines to have a winter dormancy period (see the growth cycle) and warm ripening months so the grapes can fully develop. High diurnal range is beneficial as it means the grapes experience warm days helping them to ripen and cold nights key to retaining high acid levels.
The three climate categories as mentioned above all have positive and negative factors when growing grapes. A continental climate is situated inland, away from large bodies of water (e.g. oceans). A high continentality and a high diurnal range meaning there are drastic temperature changes between summer and winter months and day and night time. Rainfall is usually more heavy in the winter meaning moulds and fungal diseases are less common in the growing season. The major negative for this climate is spring frosts and hail. Both these conditions can cause serious damage to the shoots, buds, leaves, flowers and grapes on the vine (see Weather for more information). Example of regions with this climate are Burgundy and Rioja.
A Maritime climate is characterised by its close proximity to a large body of water. This reduces both continentality and diurnal range due to the water retaining heat and slowly releasing it. Rainfall occurs throughout the year and this causes the major negative impact seen in this climate, fungal disease and rot (see diseases). An example of a maritime climate is Bordeaux.
The final climate is known as a Mediterranean climate but refers to a large number of regions, most of which are far from the Mediterranean Sea. The name is simply used to describe the factors seen in this climate. These areas are close to large bodies of water but have long warm growing seasons, with a high diurnal range but are not as cold in the winter months. The main issues here are associated with drought due to the low levels of rainfall especially during the growing season. Examples of this climate are Languedoc, Napa Valley and Central Valley Chile.
The type of soil in an area can cause the vines to behave very differently. Some soils benefit the plant with nutrients others reflect light and help ripening. Unlike most plants vines don’t need soils rich in nutrients and fertilizers are rarely used, of course if the nutrients are too sparse then the vine can also develop problems linked with malnutrition. Water is another requirement for plant growth, however vines function well under hydric stress (when water isn’t in plentiful supply and the roots have to work harder). This stress can lead to more complex, intense grapes. Rainfall is especially detrimental during harvesting as it can lead to swelling in the grapes diluting the flavours. In areas with drought issues, soils that retain water are critical, some areas such as Jerez, Spain have soils called Albariza that form a thick crust in the summer months to prevention evaporation. Soils that retain heat such as granite can aid ripening especially in areas that lack warmth. Other soils reflect the light back onto the grapes, a perfect example of this is llicorella found in the Priorat DOQ Spain. Llicorella is a combination of slate and quartz, the sparkles reflect the sun.
Unlike climate, weather frequently changes and can be different year on year. Weather has the biggest impact on vintage years. The impact of this is felt mostly in the time between bud burst and harvesting, ice and snow in winter dormancy will not damage the wine. Extremely low temperatures, far below freezing can cause harm but this rarely occurs and only places such as Canada are affected. Frost is when the temperature is around freezing point, it can often be seen on the ground during winter and looks white in colour. Winter frost has no affect on the vine however, in spring when bud burst occurs frost can destroy the new growth and therefore stop the vine producing grapes that year. Winemakers will try to prevent frosts by using wind machines to circulate the air, or by using heaters. It's one of the key reasons why the best growing sites are located on the middle to top of slopes, this reduces the likelihood of frost as hot air rises.
Hail is another weather occurrence that can cause damage to grapes. It can strip vines of leaves, flowers and fruit and holes can be created ruining grapes and leaves meaning photosynthesis is reduced. It's important to protect vines from bud burst to harvest, some produces use nets to reduce damage.
Fog can have both positive and negative impacts on grape growing. In warm to hot regions where the grapes can over-ripen and lose acidity, fog can act as a shield. The South section of Napa Valley is a great example of this as the fog rises up from San Pablo bay and the vineyards are often covered in fog up until midday. In cooler regions fog can prevent enough sunlight reaching the vines and they can struggle to fully ripen.
Rain is critical for growth of the vine, as mentioned in soils the same principles apply in terms of weather. Wind like fog can be good or bad for vines. Strong winds can cause damage, blow off leaves and grapes and even knock vines over damaging the roots. The mistral wind that blows through the Northern Rhone is a good example of how wind can negatively impact a vineyard. However, slight breezes can reduce the risk of rot and fungal diseases as they will create airflow through the vines.
Sun is the final factor mentioned here; its essential for photosynthesis, therefore key to growing the vine and allowing the grapes to ripen. Without enough sunshine the flavours will be subdued, tannins can be harsh and green and acidity levels will be extremely high. At high levels sugar levels will be high, meaning a dry wine will have high alcohol levels, flavours may appear cooked or jammy and acidity levels will be low.
These almost always have a negative impact on the grapes, Nobel rot is an example of where it can be beneficial (read the article ‘Noble rot… the stilton of wine?’ for more information). Fungal diseases occur in damp conditions where there is no air flow, the fungus attacks the plant and can damage the plant or produce stale flavours in the grapes. Fungal diseases are common in Maritime climates, spraying with pesticides or fungicides can reduce disease however, this is prohibited in organic wines. Another technique is pruning; removing leaves and bunches of grapes in order to increase the flow of air through the wine.
Photosynthesis- The process where plants use the sunlight, water and CO2 to produce energy and oxygen which helps the plant to grow.
Evaporation- When heat changes liquid into a gas state, in this case reducing the water available