Troubleshooting Your Wine
The faults and flaws and their analysis and resolution presented below are from my latest book, Modern Home Winemaking, where you can find additional information should you wish to explore these further.
WINE NOT CLEARING OR HAS BECOME CLOUDY
DESCRIPTION
It is not an uncommon occurrence that a previously crystal-clear wine unexpectedly becomes cloudy, or that, in spite of clarification treatments, a wine remains cloudy or causes filtration problems.
CAUSES
There are two main sources of persistent cloudiness or clarification problems in wines: pectin and proteins.
Residual post-fermentation pectin can cause poor sedimentation or clarification problems in wines made from high-pectin grape varieties, usually Native American varieties and hybrids, which have not been sufficiently treated with pectinases. These varieties are also more prone to pectin-related problems given their typically higher acidity, which causes pectin to become less stable and to break up into smaller compounds. Pectin is not an issue in viniferas as it is completely broken down during fermentation.
Proteins can cause white or rosé wine to remain cloudy in spite of attempts at clarifying, or cause a previously crystal-clear wine to unexpectedly become cloudy even at room temperature, but more so at warmer temperatures. It occurs in wines which were insufficiently treated; Sauvignon Blanc and Gewürztraminer are examples of wines which are typically high in proteins and therefore at greater risk of protein instability. Proteins are not an issue in reds because they bind to and precipitate with tannins. But in whites and rosés where there are hardly any tannins, proteins must be removed using a suitable fining agent.
ASSESSMENT
First determine if it is a pectin or protein instability by performing a pectin or protein test on samples.
Test for pectin: if pectin becomes hydrolyzed and the wine sample remains clear, it is then considered pectin stable; if pectin flocculates, a pectinase treatment is required.
Test for proteins: if the sample becomes cloudy, the wine is not protein-stable and must be treated. Perform bench trials to determine the minimum amount of fining agent needed to obtain a sample that remains clear after heating.
REMEDIAL ACTIONS
To treat sedimentation or clarification problems due to pectin, add pectinase to the problem wine, let settle, then rack and filter. Be sure to use an appropriate product that is effective in wine, not just juice, and follow the product instructions as doses may need to be increased in wine compared to those in juice.
To remedy a cloudy condition due to proteins, treat with bentonite or silica–gel (e.g., kieselsol/gelatin), let settle, then rack and filter.
PREVENTIVE ACTIONS
To prevent pectin problems, treat the must with pectinases, using higher doses for known high-pectin varieties.
To prevent a protein haze, perform a heat stability test on wine and treat with bentonite or silica–gel as needed.