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7 6 V I N E YA R D & W I N E RY M A N A G E M E N T | M a r - A p r 2 015 w w w. v w m m e d i a . c o m than acetic acid (1.6 g/L). These thresholds would indicate that many people can sense the pres- ence of ethyl acetate before they can smell or taste acetic acid. Acetic acid has a boiling point of 118°C while ethyl acetate has a boiling point of 77°C. Recall that ethanol typically boils at 78.5°C. Careful distillation techniques are required to remove faults associ- ated with high volatile acidity. This would require a skillful distiller, and the proper still to manipulate distil- lation temperatures and where cuts are made in terms of collection for the final distillate. Therefore, it is feasible to remove the ethanol from a high-volatile wine without retain- ing the acetic acid and ethyl acetate flaws in the final distillate. Wine oxidation can progress enzymatically through polyphenol oxidase (PPO), a common browning enzyme, or via laccase, an enzyme linked to Botrytis infections. Oxida- tion can also occur through a series of chemical reactions instigated by the integration of oxygen through production steps. A flavor byprod- uct of wine oxidation is the flavor compound acetaldehyde. It can smell like Sherry, bruised apples or plastic, depending on its concen- tration. The presence of acetalde- portion of the distillation because it contains higher alcohols and esters that can dull the character of the spirit. In some instances, heads and tails are collected and redistilled. DISTILLATION TO REMEDIATE FAULTS Faults can occur in any wine. Examples of common wine faults include high volatile acidity, oxida- tion, incidence of sulfur-containing compounds (sulfur dioxide, hydro- gen sulfide, thiols or mercaptans, and disulfides), flavor components associated with Brettanomyces contamination, and cork taint. Volatile acidity (VA) refers to the organic acids that are volatile in wines, primarily acetic acid. VA includes two aroma/flavor com- pounds: acetic acid and the break- down product of acetic acid, ethyl acetate. The concentration of ace- tic acid is regulated by the Alcohol and Tobacco Tax and Trade Bureau (TTB) as an indication of volatile acidity. Based on the Standard of Identity (Title 27 of the Code of Federal Regulations) for wine, the maximum concentration of volatile acidity in white wines is 1.2 g/L and 1.4 g/L in red wines. Ethyl ace- tate, however, has a lower sensory threshold (150-200 mg/L range) hyde also reduces the perception of freshness and fruitiness of the wine. Heavy oxygen-inducing steps in production include pumpovers or punch downs, transfer operations, headspace in tanks and barrels (ullage), mixing, filtration, and bot- tling operations. Acetaldehyde, the primary flavor compound that is associated with oxidation, has a boiling point of 20.8°C. Therefore, it can be sepa- rated from ethanol through coarse or fine distillation and manipulation of temperature during distillation. Due to the lower boiling tempera- ture, this compound will boil off prior to the vaporization of ethanol. Sulfur-containing compounds are considered faults in wines when present at high levels. High levels of sulfur dioxide, hydrogen sulfide and mercaptans/thiols and disulfides are sulfur-containing compounds that can be present as faults in wine. It should be noted that each group of sulfur-containing compounds, however, are chemi- cally different, and the only shared property of these compounds is the element sulfur in their molecular composition. Sulfur dioxide, a common wine preservative added to wines, acts as an antioxidant and, when used properly, as an antimicrobial agent. Excess addition of sulfur dioxide can result in high sulfur dioxide concentrations, masking fruitiness of the wine, and may cause nasal irritation or elicit a smell reminis- cent of burnt matches. Hydrogen sulfide, which smells like rotten eggs, has a very low threshold (<1 ppb), which can impact wine flavor negatively and compromise fresh- ness and fruitiness of wine. Mercaptans (thiols) and disul- fides also have very low sensory thresholds, typically in the ppb range. These sulfur-containing com- pounds contribute their own asso- ciated off-aromas, which include onions, garlic, canned asparagus, canned corn and putrefaction. Sulfur-containing compounds such as the ones described above can have negative effects on dis- tillates, and may not be removed effectively by distillation alone. TABLE 1: BOILING POINTS AFFILIATED WITH WINE FAULTS, ETHANOL AND WATER Chemical Compound Boiling Point (°C) Acetaldehyde 20.8 Acetic Acid 118 Ethanol 78.5 Ethyl Acetate 77 4-Ethyl Guaiacol (4EG) 234 4-Ethyl Phenol (4EP) 218 Hydrogen Sulfide -60 Sulfur Dioxide -10 2,4,6-Trichloranisole 140 Water 100