Wine and Fermentation in Pre-Industrial

Wine and Fermentation

In pre-industrial cultures, dating back to very ancient times and before the Industrial Revolution of the 18th century, the making of wine was far more practical than mere grape juice, simply because grape juice spoiled by itself if left in the open or unrefrigerated. Thus, it was easier to keep and store wine because after it was made, it did not spoil as much as compared to grape juice. According to the website "The History of Wine," grape fruit, "with its concentrated sugars and ample juice, has an inherent tendency to ferment" by itself. This process of fermentation which dates back to the ancient Babylonians in Mesopotamia some 4,000 years ago, creates alcohol when "the grapes are ripe and the juice released comes into contact with yeast" which can form from any number of foodstuffs. Thus, if grape juice itself is placed in some form of open container, "wine will make itself" ("History of Wine," Internet). This is why grape juice was not kept for consumption.

As it applies to wine, fermentation is the process which converts sugar to ethanol (i.e., ethanol alcohol) and carbon dioxide effected by the anaerobic, oxygen-free metabolism of yeast. One of the main reasons why grape juice was not kept or made before the Industrial Revolution was that it tended to spoil rather rapidly. But by the middle of the 19th century, the nature of fermentation began to be clearly understood, due in part to the experiments of French scientist Louis Pasteur who determined that ferments and their agents yeast and bacteria as primarily responsible for alcoholic fermentation. Chemically speaking, these agents act through their internal enzymes which functioning as catalysts, govern and control the series of reactions involved in the conversion of sugar into alcohol and carbon dioxide.

The process of fermentation is quite complex and can be broken down into several important steps. It should be pointed out that this process can only be accomplished by a trained fermentation/brewing specialist, at least if the resulting product is intended to be high-quality wine. First, the chemist must attach phosphate groups to the sugars. Next, a series of steps are done which the six-carbon sugar is split into three carbon pieces, one of which is then rearranged into the structure of the other. After some more rearrangements, this three carbon molecule loses its terminal carboxylic carbon atom in the form of carbon dioxide gas. The residual is the two carbon compound known as acetaldehyde which turns into alcohol if oxygen is lacking or into a multi-step series of chemical reactions that yield energy, water and more carbon dioxide, but only if generous amounts of oxygen are present.

Of course, the main organism in fermentation is yeast which can only do its chemical job if generous quantities of oxygen are available. However, it is important that this process can be modified by limiting the oxygen supply because then alcohol, rather than water, is produced along with carbon dioxide. Basically, without yeast which creates the alcohol, there would be no wine, at least not with an alcoholic base.

The progress of fermentation can be monitored or controlled in several ways. The most simple method is to observe the activity in the fermentation vessel. Sometimes in a laboratory setting, fermentation is often followed by weighing the fermentation vessel at various intervals which results in a record of the weight of carbon dioxide gas lost and exactly how much sugar remains in the vessel. The most popular form of control is a measurement of the density of a sample of the fermenting juice which can be accomplished by using a hydrometer which measures the remaining sugar's percentage in weight.

As to the taste of wine that results form this complex series of chemical manipulations by a chemist or fermentation specialist, the time required for complete fermentation of grape juice, either white or red, varies greatly. First of all, the temperature maintained in the fermenting mass is the main factor which affects the duration of fermentation, as well as the overall taste or character of the finished product. The second factor has much to do with the initial sugar concentration in the mass, the type of yeast used and the quantity of micro-nutrients in the juice itself. Generally speaking, red wine fermentation is complete within four to seven days; white wine, which is often fermented at much lower temperatures than red, often requires several weeks, months or sometimes years in the case of extremely sweet white wines.