Before bottling, wines must undergo some clarification and stabilization to remove solids, sediment, and microbial contaminants. This may include dead yeast cells (lees), bacteria, tartrates, proteins, pectins, various tannins and other compounds, as well as pieces of grape skin, pulp and stems.

Clarification stabilizes the wine and improves its clarity.

The primary clarification methods are:

• Racking
• Sedimentation
• Fining
• Filtration

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Racking

Racking is the process of moving wine from one container to another using gravity.

Alexis Lichine's Encyclopedia of Wines and Spirits defines racking as "Siphoning wine off the lees into a new, clean barrel or vessel" (a pump can be disruptive to the wine). Racking is known as Soutirage in French, Abstich in German and Travaso in Italian.

Racking helps in clarification and aids in stabilization. The process is often repeated several times during the maturation of wine.

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Sedimentation

Sedimentation is the process where solid particles in the wine, (dead yeast, grape skins, organic matter) settle at the bottom of the fermentation vessel due to gravity.

When the wine rests in tanks or barrels, the heavier particles settle to the bottom, forming a layer of sediment known as "lees."

Sedimentation is a natural process that does not require additives or mechanical intervention. It is a slow process, taking weeks or months, which may not be suitable for all schedules. Additionally, it does not remove all suspended particles, so further clarification might be needed.

Sedimentation can enhance the flavor and texture of the wine due to contact with the lees, especially in white wines like Chardonnay, where lees aging can be desirable.

For some fine wines, racking is the only clarification that is used.

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Fining

Fining is the process where substances (fining agents) are added to the wine to bind with unwanted particles, forming larger clumps that are easier to remove:

Fining agents (see below) are introduced into the wine to attract particles like proteins, tannins, or compounds that cause haze, bitterness, or instability in the wine. Once bound together, these larger complexes either settle out of the wine through sedimentation or are removed by filtration.

Fining can be a quick and effective way to remove unwanted elements from the wine, improving clarity, flavor, and stability. It can also help adjust the tannin levels and astringency in the wine.

The choice of fining agent can affect the wine's flavor and mouthfeel, sometimes stripping desired components along with the undesired ones. Additionally, some fining agents (e.g., those derived from animal products) may not be suitable for vegan or allergen-sensitive consumers.

Fining Agents

• Bentonite
  A type of clay that absorbs unstable proteins.

• Egg white
  Removes harsh tannins and clarifies the wine.
  As an allergen, in EU it must be listed on the wine label.

• Casein
  A milk protein that can clarify and remove browning from white wines.
  As an allergen, in EU it must be listed on the wine label.

• Isinglass
  Fish bladders that clarify white wines and give them that bright quality.

• Charcoal
  Removes brown colors and off-odors.
  Charcoal can over-fine removing desirable aromas and flavors.

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Filtration

Filtration involves passing the wine through a filter to physically remove suspended solids and microbes, including yeast and bacteria, which may cause haze or instability.

Filtration provides a high level of clarity and microbial stability, ensuring that the wine is visually appealing and less likely to spoil after bottling. It is a more controlled and predictable process compared to sedimentation or fining.

Some winemakers argue that filtration can strip the wine of subtle flavors and aromas, leading to a less complex final product. Over-filtration, in particular, may lead to a loss of texture and mouthfeel.

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Depth Filtration

Depth filtration uses a filter to trap particles inside the filter while wine passes through.

Filters are rated by microns (coarse, medium, fine):

• Coarse filters can polish a wine without losing its color or body.

• Medium filters will only take a limited amount of body and color out of a wine.

• Fine filters remove 80% or more of yeast and sediment and are best used after medium pads.

In the filters, particles build-up, causing pressure to increase and flow rate to decrease. When this reaches a point, the winemaker must clean the system before continuing.

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Surface Filtration

Surface filtration uses a filter that block particles on the surface of the filter.

It blocks particles larger than the filter pores, like a fine sieve or a coffee filter.

In a first filtration, a coarse filter can remove yeast particles that give the wine a cloudy appearancene.

In a second filtration, a finer filter remove can bacteria before the wine is bottled.

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Rotary Vacuum Drum

The rotary vacuum drum (1872) is one of the oldest filter methods used in wine production.

• A large rotating drum is submerged in a slurry with a mixture of wine and solids.

• The drum is covered by a cloth that acts as a filtration medium.

• As the drum rotates in the wine, particles are stucked on the surface of the cloth.

• A cake of solids builds up on the cloth, which is then removed by scraping or washing.

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Cross-flow filters

Cross-flow filters are handy because they self-cleans as it is filtering the wine. Unlike membrane filters, cross-flow filters can filter wine with a high load of particles quite quickly without the need for pre-depth-filtering.

Cross-flow filters are expensive. But, it may be worth to invest in a machine that does the whole job.

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Chapter Summary

• Sedimentation: When solids settle at the bottom of a vessel due to gravity.

• Racking: Moving wine from one vessel to another leaving sediments behind.

• Fining: Using fining agents to bind unwanted solids into removable clumps.

• Depth Filtration: Trap particles inside a deep filter while wine passes through.

• Surface Filtration: Trap particles on the surface of a filter like a coffee filter.