Monday, 20 January 2014


Most foods sold in the developed world contain substances added for a desired beneficial purpose. In the case of food preservation, many compounds are added to foods that curtail the process of oxidation and kill pathogens. With respect to winemaking, additives are used although not for the exact same reasons. It is important to remember that oxidation is always a problem with winemaking. Pathogens however do not present a problem due to the makeup of wine itself. The presence of alcohol as well as the acidic nature of wine presents an environment where pathogens cannot survive.

As pathogens do not survive within wine, additives are then used for a variety of different reasons. Without a doubt, the prevention of oxidation is the number one priority concerning wine additives. Additional concerns that dictate the use of an additive include the retardation of yeast fermenting, the removal of foul odors, the reduction of the level of iron, etc. It is important to remember that like all food products, legal policies exist for what types of additives can be used as well as how much of the additive can be used.

One of the first areas where sulfur dioxide can be applied is to the must at the pre-fermentation stage. At this point, sulfur dioxide is added to prevent oxidation and aid in the release of polyphenols for red wine production. Sulfur dioxide is continually applied throughout the remainder of the winemaking processes for the same benefits. The mechanism responsible for removal of oxygen is attributed to sulfur dioxide's reaction with oxygen. In this reaction, sulfur dioxide combines with oxygen to create sulfuric acid. This chemical reaction effectively removes the oxygen while adding an acid. One may view the addition of sulfuric acid as potentially dangerous, however the amount of sulfuric acid produced is minimal at only a few parts per million. It is also important to remember that the reaction between sulfur dioxide and oxygen is not immediate. Due to this fact, oxygen present with sulfur dioxide can still have a damaging effect on wine. The adage of avoiding oxygen exposure altogether still stands true and must be followed.

Sulfur dioxide has an additional benefit of acting as an antiseptic agent. This is important for wine production due to the fact of bacteria. If bacteria are left unchecked, the result can be the destruction of a wine. For example, the bacteria acetobacter is directly responsible for the production of vinegar and thus poses a serious potential to destroy wine. With the application of sulfur dioxide, the acetobacter are killed.

Enzymes are found in all living things and can act as a catalyst to the oxidation process. This can be seen with fresh grapes that are crushed and quickly brown or lettuce that quickly shows signs of rust. The agent responsible for the fast rate of change is an enzyme of some sort. It is important to know that enzymes are also present in wine. It is therefore fortunate that the application of sulfur dioxide to wine retards the effect enzymes have on oxidation. The usefulness of sulfur dioxide does not stop with wine. Sulfur dioxide is also used with fresh fruits and vegetables as well.

The three before mentioned areas concerning sulfur dioxide are all proactive in their nature. That is to say that the application of sulfur dioxide prevents a change from occurring. There is however a condition where the usage of sulfur dioxide is reactive in its nature. This can be seen with a wine that already shows signs of oxidation. Some wines--either through bad handling or depletion of sulfur dioxide--can develop a dull taste due to minor oxidation. With the proper application of sulfur dioxide, the wine can be salvaged and take on a fresh taste. Chemically this process occurs when sulfur dioxide combines with acetaldehyde, the compound responsible for the dull taste. Sulfur dioxide reacts with acetaldehyde converting it into an odorless and colorless compound.

As with any additive found in food and drink products, the level of sulfur dioxide must be monitored and controlled. Too much sulfur dioxide can be lethal while not enough will lead to problems with a wine. It is for these reasons that the level of sulfur dioxide is constantly monitored and controlled so that the proper ratios exist within the bottled wine.

Additional additives found within the winemaking process include ascorbic acid, sorbic acid, copper sulfate and various enzymes. Ascorbic acid is a compound commonly known as vitamin C and can be used for keeping wines extremely fresh. The addition of vitamin C without ample sulfur dioxide can create a condition where hydrogen peroxide is produced. This is an undesirable condition, as hydrogen peroxide will promote rapid oxidation. It is therefore essential that sulfur dioxide levels be religiously monitored when ascorbic acid is used.

Sorbic acid is a useful additive for wine as it prevents yeast from fermenting. For this reason, sorbic acid is a very useful additive during the bottling phase of winemaking. The use of sorbic acid does present specific problems. This can be seen in the fact that sorbic acid does not kill bacteria but rather fosters bacteria growth. Sorbic acid promoting specific bacteria growth can lead to geranium leaf tastes being present within the wine. The only way to prevent this occurrence is to introduce sorbic acid just prior to the aseptic bottling process.

The application of copper sulfate to wine is used to control a specific foul odor found within wine. Interestingly enough, the problem of foul odors within wine has actually increased with the application of stainless steel piping and fixtures. This is due to the fact that older style bronze piping and fixtures deposited trace amounts of copper into the wine. This copper acted as a cleansing agent removing hydrogen sulfide that is the source of the foul odor.

Various enzymes can be added to the wine for the control of specific wine properties. Pectinolytic enzymes can be added to control the viscosity of the resulting wine, beta-glucanase can be added to control mold problems with respect to filtration and lysozyme can be added to kill certain types of bacteria.

Sources: Core Enology Group, GrapeHeaven.

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