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Wine is browning and/or smells like Sherry

If wine starts browning unexpectedly and prematurely, particularly if it is still in bulk, this points to a more serious problem – oxidation, or oxygen converting ethanol into acetaldehyde. Depending on the extent of oxidation, the wine will also take on nutty aromas and flavors, akin to Sherry wine. These symptoms are precursor to acetic spoilage and mycoderma.

Possible Causes

Corrective Actions, if any

Oxidation due to defective or poor use of winemaking equipment, excessive exposure to air during processing or storage, or insufficient sulfite.

Lightly oxidized: Treat lightly browned whites with casein, PVPP or OptiWHITE; leave reds alone. If no change, try treating with activated carbon.

Heavily oxidized: Discard wine

The root cause of oxidation can be defective or poor use of winemaking equipment, excessive exposure to air during processing or storage, or insufficient sulfite. Browning is very difficult to correct in oxidized wine, and the smell cannot be corrected.

For reds, it is best to leave the wine alone. Deeply browned white wines may unfortunately have to go the way of the sewer.

To improve color in whites affected by slight oxidation, treat the wine with casein at a rate of 50–100 g/hL. Start at the lower end, or perform some bench trials, as casein tends to strip wine of some aromas. Dissolve the powder in cold water and add quickly to the wine while stirring thoroughly. Follow this with a bentonite treatment at a rate of 25–100 g/hL. If your bench trials conclude that casein strips out too much aromas, try using PVPP at a rate of 25–75 g/hL. Alternatively, add OptiWHITE, a specific inactivated yeast with high antioxidant properties that protects against oxidation of phenols and aromas, to improve color in whites affected by slight oxidation. Add OptiWHITE at a rate of 20–30 g/hL by first performing bench trials.

As an absolute last resort only and when other treatments are not effective, you can try “improving” color by removing brown coloration using activated carbon, available in black powder format. Add activated carbon at a rate of up to 5 g/hL directly to the wine and stir thoroughly; never add more than the maximum because activated carbon will strip color excessively and leave a carbon-like off-flavor. You should always perform bench tests on a sample before treating a whole batch. Add bentonite immediately after the activated carbon treatment, rack after a few days, and filter the wine before bottling.

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