Our third post in our wine blog series will take a look at vinification which includes acidification, chaptalisation, malo-lactic fermentation and carbonic maceration. We will follow this up by taking a look at the maturation of wine.
Yeast + Sugar = Alcohol + CO2
Yeast function between 5 and 35 degrees centigrade. Fermentation can mean be natural or controlled by temperature. With mild or cultured yeast, fermentation stops when there is no sugar left or when the alcohol exceeds 15%. Yeast number in the millions on grape skins so once the grapes are crushed, fermentation will start naturally.
Cultivated is least used in the New World wineries, and is added in the form of a dry powder which reduces the need to add Sulfur Dioxide (SO2), which is used to avoid oxidation and to kill any bacteria or yeast that could cause spoilage.
White wines are produced at 15 to 20 degrees centigrade while red wines are produced at 25 to 30 degrees centigrade.
- Acidification - Lacking in acidity, this procedure uses tartaric acid in powdered form to boost the acid. In other cases, citric acid is used instead. In contrast to acidification, if the wine has too much acid, this is solved by the addition of Potassium Bicarbonate. This procedure is most common in cooler climates. If tannin is required, it may be added in the form of a powder, or by including some grape stalks in the vat.
- Chaptalisation - In cool climates with low sugar development in the grapes, sugar is added before fermentation to raise the alcohol level.
- Malo-Lactic Fermentation - During malolactic fermentation, lactic bacteria convert the tart malic acids into the softer lactic acids. Considered to be necessary for red wines by keeping the temperature high and SO2 levels low.
- Carbonic Maceration - Bunches of uncrushed grapes, together with their stocks, are placed in vats under a blanket of carbon dioxide. This extracts color and tannin, resulting in wines that are softer and full of fruit. These wines generally do not age well. Beaujolais uses a semi-carbonic maceration for the bulk of its wines.
Most wines are made for early drinking, requiring the minimum of maturation. A more fine wine will benefit from some period of aging, whether in bottle or cask, especially reds. To survive medium or long term aging the wine will need high levels of tannin, acidity or alcohol. Using oak in aging is for the winemaker to decide. Simply, the better quality the wine the greater the need for barrels, adding tannin into the wine and also softening some of the other characteristics, by means of slow oxidization.
Selecting what oak barrels are used is finding how it has been cut, aged and whether it has being toasted or not. Small casks have a more marked effect on the wine than larger ones via a greater ratio of wood surface to wine. One small cask is called a barrique, containing two hundred and twenty five liters, equaling three hundred bottles, or 25 cases. New oak adds aroma and flavors of oak to the wine, a vanilla or smoky character and adds wood tannins. This effect is lessened as the caskets older.
After four years there is very little flavor or tannin added. Normally, a casked wine red will spend of max of eighteen months to two years in oak before bottling. The casks are topped out regularly (called ouillage) and racked every six months.
Wine Fining and Filtration
Before the final racking, the wine will usually be fining to settle anything in the bottle. Wine has certain deposits that are removed with addition of a fining agent such as Bentonite or albumen done after racking. To prepare the wine for bottling, it has to be filtered to ensure that it is perfectly bright. Most wine is filtered through a plate filter, then bottled.
Visit us next week when we take a look at Wine Temperatures.
Come and visit Morgans Restaurant and Wine Bar and browse through our extensive wine menu.