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Pre Fermentation Adjustments

by Staff Writer - B. Shaughnessy | February 08, 2012

Today more than ever technology has allowed the vintner to precisely control most of the winemaking processes. This can be seen in the fact that within some of the most inhospitable climates, decent quality wines are now being produced. As with any regulated commodity, the amount of adjustment allowed within wine is subject to local laws and regulations. With respect to the must generated during the juicing phase, adjustments are absolutely necessary for the production of a good quality wine. Vintners must bear in mind specific criteria concerning the adjustments of the must. This criteria includes local laws, preconditions of the must as well as knowledge obtained concerning experiences with winemaking.

It should be noted that adjusting the natural balance of wine is a critical and tedious process. Due to an increased understanding of the chemical makeup of wine, vintners can make adjustments to compensate for a lack of natural balance found in the original grape crop. It is important to understand that only so much of the original grape crop can be effectively influenced. There comes a point where tinkering with the chemical breakdown of the wine does more harm than good. The old adage that nature knows best can be seen as words of wisdom with respect to making drastic adjustments to the must. It is also important to remember that some adjustments are very positive and absolutely necessary for the production of quality wine.

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The adjustments and controls available to the vintner prior to fermentation include the retardation of oxidation & pre-fermentation, the process of clarification for white wines, the adjustment of the amount and type of acid found within the must, the control of the amount of alcohol found within the final wine and finally the control of the necessary amounts of nutrients required for yeasts to grow. It is important to remember that natural processes exist for the regulation and control of the before mentioned areas. However, with today's marketplace of quality wines, vintners cannot rely simply on Mother Nature for process control.

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The damaging effects of oxidation are universally known. These damaging effects begin the moment the grape is harvested. If left unchecked, oxidation can wreak havoc on the final wine. It is therefore important that oxidation of the must be controlled before fermentation occurs. Indeed, oxidation is not the only enemy of the must. The yeasts found in nature can also start the fermentation process before the must is ready. To control the process of oxidation and pre-fermentation, vintners rely on an application of sulfur dioxide to the must. The application of sulfur dioxide works well for controlling the oxidation and pre-fermentation of white wines. With red wine production however, the effect that sulfur dioxide has on the must is somewhat different. Within the must of red wine, natural microorganisms exist that remove the sulfur dioxide through molecular processes. In this instance the application of sulfur dioxide may seem academic. It is important to remember that other benefits do exist with respect to sulfur dioxide. The application of sulfur dioxide to red wine must does have the side effect of releasing polyphenols.

After the must has been treated for the effects of oxidation and pre-fermentation, the processes for white and red wines diverge slightly. This can be seen in the process of clarification, which is used early on in the production of white wines. Clarification is the removal of cellular matter from the resulting must. One may think of clarification as a filtering of the juiced grapes. The proper removal and balance of this cellular matter is of the utmost importance. Too much cellular matter will create an off-flavor within the wine. However if too little cellular matter is found within the must, the yeasts will be lacking nutrients required for the process of fermentation. Technologies available for clarification include natural settling over a period of several days, forcing the wine through a centrifuge (much like how cream is separated from milk), or the process of injecting small bubbles of nitrogen into the must causing the cellular matter to float. Whatever the process, it is important to remember that balance is the key.

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One of the most important factors effecting the balance of a wine is the amount of acid found within the wine. Acid levels are monitored before fermentation and can be easily adjusted. As mentioned earlier, it is best not to upset the natural balance too much. Also, it is important to realize that many locales have regulations of just how much acid can be added or removed and of what type. For the process of adding acid, a simple measurement of the must is performed and the vintner makes a decision for the amount of acid to add. Different acids are available, but the acid most used is tartaric acid as tartaric acid is found naturally in grapes. With respect to acid reduction, the removal of acid is not a simple of a process. This is because acids cannot be filtered out of the must. Instead a chemical process must be used to remove the acids. Compounds such as calcium carbonate or potassium bicarbonate are used for this purpose.

One of the most important characteristics of wine is the alcohol content of the finished wine. The agent directly responsible for this is the amount of sugar found within the grape juice. During the fermentation process, yeasts metabolize sugar to produce alcohol. Therefore the more sugar found within the grape juice, the higher the alcohol content of the resulting wine. In the early 1800s the addition of sugar to must for the purposes of enrichment was officially recognized. Since that time various locales have passed laws regulating the amount of sugar that can be added to the must. It should be noted that the process of adding sugar--also known as Chaptalization--can be disastrous if taken to the extreme. Adding too much sugar to the must dilutes the flavor found in the final wine. Other processes do exist for increasing the sugar concentration of the must. Rather than add sugar to the must vintners now have the option of removing water from the must. The removal of water concentrates the must and produces similar affects as the addition of sugar.

One of the last adjustments to be made before fermentation are the inspection of nutrients found within the must. Proper nutrients are required for the yeasts to successfully metabolize the sugar into alcohol. Combined nitrogen is required for fermentation and if the must is lacking combined nitrogen, an ammonium compound can be added to the must.

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