Wine grapes, Vitis vinifera, grow easily in any temperate to warm climate. A solution of sugar and water develops in ripe grapes and the skins easily allow the growth of natural yeasts. In the fermentation process, these single cell organisms consume the natural sugar and change it into ethyl alcohol and carbon dioxide. This rather simple process has been observed and used for thousands of years in human culture. In the past hundred years or so, technology and new ideas from winemakers have played an ever-increasing role in the making of wine. It’s becoming more and more a science and an art. Here are the basic principles of winemaking. The grapes are either harvested by hand (this is best), or with mechanical harvesters. Exposure to air should be kept to a minimum at all stages of the process. Sometimes powdered sulfites are sprinkled on the grapes prior to crushing to prevent too much reaction with the air. The fermentation usually takes place in open vats. Several processes may be employed to give the wine clarity: fining and filtration for example. Shortly after fermentation has ended, the wine is transferred to a settling tank where filtration and other clarification techniques may be used.
The Differences Between Red Wine and White Winemaking
There are significant differences between red wine and white wine production. Basically, red wine is the outcome of crushed, fermented grapes. White wine is the outcome of fermented grape juice (that is, no skins or meat of the fruit). Blush wines, out of interest, are made from red grapes that are made into wine as though they were white grapes. The red grape skins add a bit of color and nutrients to the juice being made into blush or rosé, leaving a slight blush of red in the wine.
All grapes contain the same kind of green fruity-meat, but red grapes have red skins and in the winemaking process, there is a considerable amount of color, flavors and tannins that are imparted to the final product. After crushing, the red grapes, skins and all, sit in a fermentation vat for a period of time. Picture a huge plastic bin with a mixture of crushed grapes and juice with a layer of crushed wet skins on top. The skins tend to rise to the surface of the mixture, forming a layer on top. This top layer is frequently mixed back into the fermenting juice (called must). After fermentation has stopped, about one to two weeks later, the new wine is drawn from the vat. A bit of “free run” juice is allowed to pour and then the remaining must is squeezed, yielding “press wine”. The wine is clarified and then transferred to oak aging barrels so that it may mature. When the winemaker considers the wine ready, it is transferred to bottles and labeled.
Right after picking, white grapes are put into a crushing machine. In the process, the skins are separated from the juice, an important difference over the red wine process. Some adjustments are sometimes made to the acid or sugar levels at this stage (the addition of sugar is called “chaptalization”). The clarified juice is then ready for fermentation. Yeast is then added to the juice for fermentation. Before long the white grape juice becomes white wine. At this point, some further tinkering is usually called for: filtering, and perhaps the addition of sweeter juice to round out the flavor. The wine is then aged by storing in oak or stainless steel containers, and after a few months, it is bottled.