Wine Faults and Flaws
Wine Hazes and Deposits
Browning
Browning is a color defect that is phenolic in nature and is more often found (because it's more easily seen) in whites rather than reds (Figure 16.2). Reds, however, can be affected but tend to exhibit browning (loss of color is an ancillary effect) later in life. Browning can be caused by oxidation due to oxygen exposure, inadequate sulfur dioxide levels, or the activity of the enzyme laccase from Botrytis-infected fruit.
Prevention and Treatment
Harvesting clean fruit unaffected by Botrytis minimizes laccase activity and pressing whites soon after can reduce the chances of browning. Polyvinylpolypyrrolidone (PVPP) is an insoluble synthetic fining agent in the form of a cross-linked, resinous polymer that functions like a protein when binding to phenolic compounds.
Pinking in White Wines
White wines that have been made using highly reductive conditions (i.e., minimizing oxygen by using inert gases) can sometimes develop a pink coloration on sudden exposure to air. The aroma and flavor often remain unaltered.
Prevention and Treatment
Harvesting clean fruit and processing it quickly as well as minimizing air contact is very useful in preventing pinking. Usually, increasing the level of antioxidants (free sulfur dioxide to 45mg/L, and/or ascorbic acid to 10mg/L) will be sufficient to protect the wine from the oxygen pick-up at bottling that leads to pinking. If, however, the problem persists, the wine should be fined with PVPP or casein.
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