|
Introduction |
|
MAKING WHITE WINES The white grape varieties normally ripen two to three weeks before the red ones. All grapes are hand picked into plastic baskets which carry about 15 kg of grapes. Small baskets are used to ensure that the grapes on the bottom are not crushed by the weight of the top ones. The baskets are also perforated so that if there is rain, the rainwater will drain away. In this way we can be certain that the berries reach our cellar in top condition. The baskets are transported on specially made tractor-trailers which can transport three pallets of baskets each. One pallet contains 20 to 25 baskets, so one trailer will transport about 1000 kg of grapes. The pallets are placed in the shade to wait for processing. All the grapes are hand-sorted on a vibrating conveyor table even though they have already been selected in the vineyards. In this way we can ensure that no rotten or unripe berries or leaves get processed further. The grapes are first separated from their stems by a mechanical de-stemmer. Then a vibrating table transports the bunches to a crusher-destemmer, where the grapes are separated from the stems, and are lightly crushed. At this stage, a small amount of sulphur dioxide and in some cases some ascorbic acid is added to prevent the juice from becoming oxidized. This also reduces the number of undesirable microbes that have been transported to the winery on the grapes. Cooling Before PressingUnder the crusher there is a pump with a large hopper into which the crushed fruit falls. A screw at the bottom of this pump forces the fruit into a hose that takes it to our press. Skin ContactMore flavour components can be extracted from the berries if they are left to macerate for some time before pressing. In most instances, the flavour components of grapes are found just under the surface of the skins. If the grapes are in healthy a condition, the juice of the grapes can be left in contact with the skins for a short time. This useful process is called 'skin contact' or 'maceration'. Sauvignon Blanc being acid and highly aromatic benefits mostly from this maceration process. Normally one press load of grapes is sorted at a time, and as the press capacity is 5000 litres, about five trailer loads can be processed at once. If the grapes are not in excellent condition, then the juice should be separated from the skins as soon as possible. If the grapes are healthy, larger amounts of fruit can be processed at one time, as the fruit can be left to macerate in contact with the skins for periods of up to 10 hours. Over the press there are two rotating "Vinimatics", which although meant mainly for red wine making, are also well suited for use in the maceration process. The fruit can be left in contact with the skins before being emptied directly into the press below for the pressing process. High-Tech Machinery At Carsin we use a so-called pneumatic tank press. This press looks like a large cylindrical tank lying in a horizontal position, and it can turn on its axis. Inside, a plastic membrane is attached to one side, whilst on the other side is a series of drains. These drains feed into a tray suspended under one end of the press. Compressed air can be pumped in behind the plastic membrane, thus forcing the crushed grapes up against the drains opposite. This action forces the juice into the drains from where it falls into the tray below leaving the skins and seeds inside the press. The pressure used to carry out this pressing process can be accurately controlled so as not to press too harshly as this would extract tannins and other undesirable products. The pressure is increased gradually and the entire process is computer-controlled. Pressing one load of fruit normally takes between two and three hours. For each load the press is first filled with carbon dioxide. Then it is filled with fruit so that contact with air (oxygen in particular) during filling, is minimised. From the tray the juice is pumped into one of our stainless steel tanks. This pumping process is automatic, being controlled by a floating level switch. At the bottom of the tray, there is also a valve which can let in nitrogen gas. Nitrogen can be used to ensure that no oxygen comes into contact with the juice in the tray, as the gas provides a 'blanket' over the juice. To avoid long-term oxidation nitrogen is used to push the oxygen out of from the juice and so it is allowed to flow with the juices as it is being pumped. Newly pressed juice should always be green. If it is oxidized, it will soon turn brown just as half eaten apples do when they are left in the open air. Juice Clarification The juice is further cooled in stainless steel tanks. The object of this cooling is to get the grape solids to settle out of the juice and to prevent fermentation from starting. As the juice is cooled down to 5 - 10 degrees Celsius, the bigger pieces of grape skin and flesh that are not separated during the pressing process, drop to the bottom of the tank. This settling occurs much faster if natural enzymes are added to the juice. As the solids fall to the bottom, the juice becomes clearer. Alcoholic Fermentation After partial settling, the juice is taken away from the solids by pumping it into another tank for fermentation. We buy yeast in a dried form, just like baker's yeast. After rehydration it is added to the juice. The juice will slowly warm up and the fermentation will start. As by-products, fermentation produces carbon dioxide and heat. Thus, the temperature of the fermenting wine has to be controlled. If the temperature rises above 18 degrees Celsius, the cooling system will be turned on, and the cold glycol will circulate in the cooling plate at the back of the tank. At Carsin mainly cultured yeasts are used. They ensure uniformity and easy control of the fermentation process. Some other practical problems which could otherwise make life difficult for the winemaker include "off-smells" and "stuck" fermentation, where the yeast has failed to transform all the sugar in the juice into alcohol. Controlling the temperature allows the winemaker to produce wines with more aromas, as less of the volatile aromatic substances are driven off. Fermentation is monitored by checking sugar levels. At the end of fermentation, the wine is again cooled with the aid of the cold glycol. Fermentation in Barrel During the 1991 vintage, a small experiment was carried out. It involved fermenting some of the juice in new oak barrels each holding 225 litres. Fermenting grape juice was transferred into the barrels. At the end of fermentation, the wine was left in contact with the dead yeast cells inside the barrel. As in the old white winemaking tradition, this sediment was stirred into the wine once a week. The result was a fatter wine with more complex aromas, "stronger structure", as well as better length. We produced part of our Semillon wines in this way until the 2002 vintage. Nowadays only our Sauvignon Gris -grapes are vinified - ie. fermented - in barrels, although most of the barrels which we use are not new ones but rather one or two years old. Also some heavier Sauvignon Blanc juices are sometimes vinified in barrels with the aim to make wines which can age in bottle for many years. One restriction is the high price of small barrels, which cost about 3000 francs each if produced from French oak. Currently we buy around 70 new barrels each year and we also used one and two year old barrels. One barrel will hold the equivalent of 300 bottles! Ageing At the end of fermentation, the wines stored in tanks are maintained at relative cool temperatures. In this manner we aim to keep them fresh and fruity. In some cases they can be left in contact with their yeast solids, just in the same way as they are in barrel. But this is very dependent on the quality of the juice and the style of the final wine. By maturing the wines in wooden barrels, we are introducing complexity into the wine. The more the barrels are "toasted" during their production, and the younger they are, the more vanilla, toffee, and other such spicy flavours will be diluted into the wine. When wine is matured in barrels, it also undergoes complex oxidation reactions. Wood, being porous, allows the wine to 'breathe' and so a controlled amount of oxygen enters the wine. During the period of barrel maturation, it is important that the barrels are kept full so that this oxygen exchange only happens through the pores of the wood. The barrels are topped up with wine at least twice a week. The length of time that the wines are matured in barrel is related to the style of wine. Our l'Etiquette Grise -wines will normally age for about 6-8 months in oak. The barrel ageing gives the wine quite a pronounced aroma, especially if we use new and heavily toasted oak. The French wine laws state that we are not allowed to add anything to the wine which gives it some taste. Barrels are still allowed to be used as containers for wine. But much cheaper oak chips, which are used in many other countries, are not allowed."Put wine into oak, not oak into wine!" state the French. Other "Additives" Various substances are added to the juice or wine during the above processes. As already mentioned, ascorbic acid and sulphur dioxide are used in small quantities to avoid oxidation. The sulphur dioxide also kills some of the yeast and bacteria that are naturally present on the grapes. Enzymes can be added to help the juice settle. These are pectolytic enzymes that are already present in the grapes, and so we are just increasing their levels to speed up the settling process. By French law, acid can also be added, but only if sugar is not used to increase the alcohol content of the wine. Ideally we want to make acid additions to the wine as early as possible, i.e. before the fermentation process. Various different types of acid can be used. Tartaric acid is the most abundant grape acid and so it is the usual choice. We do not acidify our wines. A whole range of fining agents is also used. They are used to help the wines settle and/or to make flavour modifications. Bentonite (a type of clay) is a fining agent that helps the fermented wine to settle and removes excess protein, which can cause haze in the wine. If one is dealing with difficult and rotten fruit, some casein (a milk protein) can be introduced to get rid of the flavour and odour of rot in the juice.
French law stipulates that sugar can be added to fermenting juice in
years when the grapes are not ripe enough to produce a sufficient
level of alcohol. Alcohol is the second most abundant compound in
wine. It plays an important role in the flavour profile of wine. This
process, called chaptalisation, has become very common practise in
some European wine-producing regions. Chaptalisation can improve
certain wines in years when it is impossible to harvest the grapes at
higher levels of ripeness. It should be noted that grapes do not
always reach optimum flavour at the highest possible sugar level in
any given year. The grapes can reach a maximum maturity in flavour
before maximum sugar levels are reached. But in some cases producers
prefer to harvest the grapes very early, thus lowering the risk of the
effects of possible bad weather. But by doing so, they also lose a
substantial part of the flavours which would otherwise be gathered
during the marginal maturation time. The possibility of being able to
chaptalise should not be abused.
|
|
