Fining Wine for Color, Off-Flavors, and Off-Aromas
In addition to fining for clarification and to reduce astringency wines are often fined for color reduction as well as to remove off-flavors and off-aromas. Activated carbon, casein, copper sulfate, and PVPP are typically the agents of choice.
In wine, activated carbon can be used for removing off-flavors and aromas of various kinds and to decrease browning or pinking in white wines. The carbon type most suitable for decolorizing is marked as KBB, and the deodorizing type is marked as AAA. As mentioned above, carbon works well in combination with PVPP in both tasks.
Casein finds its principal application in white wines for the removal of color or color precursors, oak character, perhaps bitter components, and infrequently to enhance clarification. Casein can bind with and precipitate oxidized phenols, thus helping to remove and prevent brown formation.
There are a few wine off-aromas that can be removed by fining, while others are unassailable. The most common is hydrogen sulfide, which causes the rotten egg aroma that winemakers refer often referred to as reductive characters.
As previously mentioned, polyvinylpolypyrrolidone (PVPP) binds with and removes the smaller, phenolic species such as the catechins and anthocyanins, which are precursors of browning and pinking oxidation reactions in white wines. Several white wines, such as Sauvignon Blanc, have a tendency to turn pinkish within days of oxygen exposure, especially those protected from oxidation during and subsequent to crushing.
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