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Components of the Fermented Must

by Staff Writer - B. Shaughnessy | February 09, 2012

The production of any alcoholic beverage is an interesting study from a chemical and component point of view. From start to finish, different components are present at different processing stages. Natural processes are responsible for converting these components into different substances. With respect to winemaking, the process begins with grape juice along its various constituents and winds up with wine. Understanding the various chemical components of wine is important for the vintner producing the wine. Also equally important is that consumers have an understanding of the components of a wine.

The most important step within the winemaking process--and the step responsible for the most change--is the fermentation step. Fermentation is the process where simple grape juice is converted into alcohol. The various components of grape juice--sugars, acids, minerals & nutrients, polyphenols and anthocyanins-- provide resources to yeasts for the production alcohols, additional acids and glycerol. The resulting wine is a liquid that is chemically different that the raw grape juice.

Perhaps the most recognizable component of wine is alcohol. This is a logical statement, as the main process of the fermentation stage is the production of alcohol. However, it is important to realize that many different types of alcohol can be produced and that monitoring and controlling the alcohol being produced is of the utmost importance.

In wine as with any alcoholic beverage, the main source of alcohol comes from ethyl alcohol. Ethyl alcohol is the substance that when consumed, is responsible for the mood altering reactions found within human beings. Different alcohols are found within wines, each having different concentrations and different characteristics. The first such alcohol is known as methyl alcohol. Methyl alcohol is a substance that poisonous to human beings and if consumed in large enough quantities causes a person to become ill. Illness is followed by an onset of permanent blindness, madness and finally death. The good news is that methyl alcohol is present only in very small amounts of controlled wines. The term of controlled wines refers to the fact that many governments look to prevent the spread of badly concocted spirits and wines. All wines professionally bottled and sold may have traces of methyl alcohol, however these traces are minute and pose no health risks. Additional alcohols are produced during the fermentation process, many of which have larger molecules that ethyl alcohol. While these alcohols also have unpleasant side effects, these alcohols are also only seen in trace quantities within the final wine.

The trace quantities of noxious alcohols may sound unappealing, but the fact that these alcohols exist within wine at such small quantities makes them of little consequence from a health point of view. The inclusion of noxious alcohols is important, as these alcohols are responsible for the creation of esters. Esters are chemical compounds that are responsible for the aromas found within wine. Scents such as pineapples, strawberries, raspberries, etc are all created by the production of esters. The esters themselves are created during the maturation process when alcohols react with natural acids. This helps explain why fermented wines contain additional aromas not found within the original grape juice of the wine.

Generally, the vintner does not take into account the amount of alcohol when determining wine quality. This is not to say that alcohol content and wine quality are not related. On the contrary, alcohol is required for quality wines. The proof of this can be seen when sampling alcohol-free wines. Alcohol has a desensitizing effect on the taste buds and as such changes the way in which a person perceives tannins and acids. The overall point concerning alcohol is that like everything else, proper control of alcohol levels is absolutely essential.

The next major constituent of wine would be the acids found within the wine. As discussed in wine literature, grape juice contains two major acid types prior to fermentation, malic acid and tartaric acid. The fermentation process--mainly the biomechanical action of the yeast--is responsible for producing many additional types of acids. Acids such as lactic acid and succinic acid are present, with many additional acids present. The presence of these acids is important, as they are required for the production of esters. The control of the concentration of acids is important and should be confined to winemaking stages occurring before fermentation.

Other components of wine include residual sugars and glycerol. Residual sugars are sugars left over after the fermentation process has stopped. As the fermentation process is responsible for converting all sugar into alcohol it may seem impossible that wine would have any sugar left within it. It is important to remember that vintners control the final taste and therefore have the ability to stop the fermentation process so that some sugars are residual. It is interesting to note that the sugar level of a resulting wine can be altered by blending different wines together but not by adding sugar. The addition of sugar after the fermentation process is a technique not approved by many different locales.

Glycerol is another component found within the final wine. Glycerol is the third most abundant component found within wine, behind water and alcohol. The production of glycerol in wine is directly related to the sugar in the grape juice. Glycerol plays an important role with the feel of wine. An addition of smoothness without unpleasant sweet properties is a good description of the feeling glycerol provides to wine. Finally, glycerol is thought to influence the legs that are formed by wine when observed in a glass.

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    • MARIE-LOUISE
      Sep 16 2014 4:59 PM
    • Greatly appreciated this article would like to learn more

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