Wine Faults and Flaws
Causes of Wine Faults and Flaws
This fault is quite rare these days. Although it still happens occasionally, it can be easily prevented. The metals of concern are copper, iron, and to lesser extent aluminum. The two most often encountered metal hazes are copper and iron. These hazes occur when the wine contains high levels of the individual metal. Grape processing and winemaking equipment, filter pads and even bentonite (iron) may be the source of these metals in wine.
When white wines have not been protein stabilized with bentonite, or insufficiently stabilized, a protein haze may form over time or if the wine becomes warm. Protein hazes are cloudy/grainy and if the protein complexes become large enough, they can settle out as a granular sediment. Protein precipitates are not as heavy as tartrate deposits and may remain suspended in the wine for some time before they settle to the bottom.
Phenolic molecules can polymerize and precipitate much like protein molecules. So, phenolic materials can produce hazes and unsightly bottle deposits in red wines.
Potassium bitartrate (KHT) crystals, often referred to as wine diamonds, are usually all precipitated out of a wine during the cold stabilization process before bottling. Although alcohol levels and pH play a role, the saturation equilibrium for KHT crystals is largely temperature dependent. Thus, KHT crystals may be formed in the bottle when the wine is cooled below its stabilization temperature (Figure 16.1).
Microbiological Hazes and Deposits
The growth of yeasts or bacteria in bottled wines can cause turbidity and a sediment. Saccharomyces and Zygosaccharomyces will form a yeast lees deposit if allowed to referment in wines with residual glucose and fructose. Zygosaccharomyces may grow without fermenting (i.e., without producing carbon dioxide and alcohol) using sorbate as a growth substrate in wines where sorbic acid has been added. In these instances, larger granules are formed.
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