This is the first article of a three part series exploring wine fermentation:
- Fundamentals of Wine Fermentation
- Chemical Reactions during Wine Fermentation
- Unconventional Methods of Wine Fermentation
Wine making is a true art. The vast majority of the time most of us savor our favorite wines with little consideration to the precise control with which it was made. Granted, reflecting on the exact and complex chemistry that was used to create such superb vintages every time you consumed wine would no doubt ruin the experience, but possessing a rudimentary knowledge of wine fermentation aids in developing a skill for wine tasting and also instills a deep appreciation for the care and effort used to create such masterpieces.
Fermentation is a biological process that occurs in nature without human assistance. Humans, however, have learned to harness this process and use it to create wonderful edible delights. As with most fermentation, yeast is the main proponent of the finished product. These nucleated micro-organisms are adept at metabolizing sugar and various elements such as carbon, nitrogen, sulfur, and phosphorus consequently producing alcohol as a byproduct. Yeast that exists naturally on ripe and harvested grapes is called “ambient” yeast. Originally, wine making utilized ambient yeast almost exclusively. But due to undesirable traits because of limited control over wild yeast, winemakers have learned how to develop and acquire more controllable strains.
Fermenting grape juice into wine is a delicate process. Winemakers go to great lengths to accurately monitor temperature, metabolic speed, and oxygen exposure during wine fermentation. Temperature plays an important role in wine making. An environment that is too cold can slow down the fermentation process and excess heat can force the yeast into inactivity or kill the yeast prematurely. Wine makers keep constant control over the internal temperature of the must (freshly-pressed fruit juice). White wines are generally fermented between 65-68 degrees Fahrenheit and red wines are usually fermented at higher temperatures. Similarly, when aging wines in your home, it is highly recommended that you store them in a wine cooler that will allow regulated temperature control.
The amount of oxygen exposure is another element of wine fermentation that requires finesse. Fermenting grapes can easily oxidize producing undesirable characteristics. Therefore, wine makers will allow more exposure to oxygen during the primary fermentation period, often fermenting the must in open stainless steel or wooden vats for around one to two weeks. During the second fermentation, which is often more of an extension of the first, the oxygen exposure is reduced when the wine is relocated to wood barrels or another type of closed vessel. This period of fermentation often lasts for approximately 5 to 10 more days.
The fundamentals of wine fermentation include choice grapes, a premium yeast strain, and a precisely controlled fermenting environment. Part 2 will elaborate on the complex chemical reactions involved in wine fermentation and their influences on the expression of the wine.
Guest Post By Sarah Meadows