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Clarification Processes

by Staff Writer - B. Shaughnessy | February 04, 2012

With winemaking's key process being the fermentation stage, it may seem logical that a wine is ready for consumption when fermentation is complete. Unfortunately wine tasted immediately after fermentation reveals a different picture. Wine tasted immediately after fermentation presents itself as a vile concoction that can actually lead to minor health problems if consumed in large amounts. This is due to the fact that while fermentation has converted grape juice into wine, the immediately fermented wine contains various other undesirable substances--dead yeast cells, for example. These undesirable substances must be removed so that the true characteristics of the wine are made available to the drinker.

The nature of wine as described in the previous paragraph is a problem that has presented itself to vintners for as long as winemaking has been practiced. Ancient techniques such as allowing the impurities to settle out of the wine as well as using a fining agent are still used. Newer techniques such as chemically extracting undesirables are also available. Whatever the technique used, it is important to use proper clarification procedures in order to produce the best possible wine that the consumer has come to expect.

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As with all winemaking processes, care must be given to prevent oxidation. The clarification processes are no exception to this rule. Oxidation outside of the maturation stage will cause the wine to break down into vinegar. As discussed in wine literature, the action of sulfur dioxide is effective in preventing oxidation of the wine. However, the production of carbon dioxide in the fermentation step naturally removes any free sulfur dioxide present within the grape juice. It is therefore extremely important that sulfur dioxide be added to the wine immediately after the fermentation process has completed.

One of the first natural clarification processes begins immediately after the fermentation step has been brought to a halt. The natural process of gravity causes small particles to settle to the bottom of the vat that holds the fermented wine. This process is known as racking and usually takes several days to complete. During this time dead yeast cells and grape cellular matter separate themselves from the wine. The wine is constantly observed during this process and when clear enough, the wine is pumped into a different storage vessel. If done properly, the dead yeast cells and cellular matter remain in the fermenting vessel.

When viewing the process of racking in a modern winery with high throughput volumes, the inefficiencies of the process become noticeable. For many wineries racking is too slow of a process to be used on a large scale. Also, there are consequences in allowing the wine to spend too much time with the dead yeast cells. The dead yeast cells and grape cellular matter are known as "the gross lees" and exposing a recently fermented wine to these gross lees runs the risk of damaging the wine with an unpleasant bitter taste. This combined with the amount of time required for racking has led to wineries using an oxygen-free centrifuge to remove the gross lees.

Immediately after the racking process but before additional clarification processes, the vintner samples the wine to determine if blending is appropriate. Blending is an important process within winemaking and when used appropriately has positive effects on the resulting wine. Unfortunately, many people involved with the winemaking process view blending as a somewhat shady practice. This viewpoint is false. Blending is performed at nearly all wineries in the world and in some of the finest wines. As seen in the finest wines, blending uses the finest wines produced from the finest grapes grown within the finest parcels of the vineyard. In most cases when wine is blended at even the smallest levels the results can be spectacular.

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The next clarification process after racking and blending is known as fining. Fining is an ancient process where a naturally occurring protein or clay is added to the wine. This protein or clay works to remove undesired molecules resulting in an improved balance to the resulting wine. The mechanism in which fining works is very interesting. Fining provides a way to remove particles too small to be removed by simple filtration.

Particles that exist within wine are abundant. Some of these particles are proteins known as colloids. Several different types of colloids are present with some being stable colloids and some being unstable colloids. Stable colloids present no problems to the wine while unstable colloids represent a problem in making wine cloudy over time. It is important to realize, for reasons not fully understood, molecules and particles found within wine contain electrostatic charges of either positive or negative. The unstable colloids are no exception and carry the same electrostatic charge among them. Based on this fact, a protein or clay with the reverse charge is added to the wine causing the unstable colloids to become attracted to the added material.

Several different protein sources are available, however in modern times many wineries have concentrated on using only a type of clay known as bentonite. In the past protein sources such as ox blood and egg whites have been used. With animal diseases--such as mad cow disease--the use of these materials has fallen by the way side. Gelatin, isinglass, casein and even tannins are all used as fining agents with different properties being observed by each substance. Regardless of the fining agent used, the procedures are the same. The fining agent successfully attracts the undesirable small particles together. The combined fining agent as well as the unwanted particles are then removed through another round of racking, either by settling or centrifuge.

Blue fining is a relatively recent process used to remove iron and copper ions from the resulting wine. Excess iron and copper can lead to a haze or even solid materials found within the wine. Excess copper left within wine can also act as a catalyst to oxidation. The chemical technique developed to remove excess iron and copper is the introduction of potassium ferrocyanide to the resulting wine. Contrary to the name, potassium ferrocyanide is only slightly toxic and in the case of blue fining is used in low doses. The introduction of potassium ferrocyanide causes a reaction with iron and copper and as a result produces a deposit of ferric or cupric ferrocyanide. While the process of blue fining is beneficial, there are some drawbacks. The first drawback is that blue fining must be performed by a qualified chemist. This is because while potassium ferrocyanide is only slightly toxic, there is a chance that a toxic derivative of cyanide can be synthesized. Fortunately the production of toxic cyanide can only occur if all iron and copper are removed from the resulting wine. As iron and copper are needed in small quantities within the wine, the production of toxic cyanide is successfully checked, as all potassium ferrocyanide would be removed from the wine before all iron and copper are removed. The second drawback is that certain locales prohibit the use of the blue fining process.

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