Wine is an alcoholic beverage made from the fermentation of grape must (Elias, 2012). It is a complex product that takes extreme care and caution throughout every stage of production. The overall quality of the final wine is a sum of each step in the process. Should a miscalculation or misstep occur along the production line, the final beverage can be affected. These defects, which will be referred to as faults, decrease the quality of the wine and the degree to which it will be enjoyed by the customer. There are ways to remediate these defects, one of which is by distilling the wine into a high proof spirit. The following paper will discuss faults in wines and how some of these faults can be remediated through distillation.
Distillation is a process by which a low proof alcoholic beverage is heated in a controlled process in order to separate ethanol from water and other components, with the ultimate goal of concentrating the ethanol into a high proof spirit (Berglund, 2004). Wine or beer is first produced from a fruit or grain base, respectively, that has been fermented with yeast prior to distillation. The wine or beer is then placed into a still where a heat source is applied. There are two types of stills: column stills (Image 1) and pot stills (Image 2) (Berglund, 2004). Each uniquely separates ethanol from other organic compounds.
The separation of ethanol occurs because ethanol boils at a lower temperature than water. When heat is applied to the wine or beer base, ethanol boils before the water in solution. The ethanol vaporizes, rising to the top of the still, where it collects and then is sent to a condenser where it is quickly cooled. The water and other organic compounds are later removed from the heated unit of the still (Claus and Berglund, 2005).
As wine and beer are not pure compounds, their boiling temperatures will vary. Pure water boils at 100oC and pure ethanol boils at 78.5°C (Ackland, 2012). There are other compounds present in the mixtures that will boil at varying temperatures below 78.5°C, between 78.5°C and 100°C, and above 100°C (Table 1). The first compounds to boil, condense and be collected are often low molecular weight organic compounds such as methanol. These compounds are undesirable in the collected distillate. This portion of the distillate that is collected in the beginning of a still run is referred to as the "heads" or "forerun" (Berglund, 2004). Once the low molecular weight compounds have boiled off, ethanol is vaporized. This portion of the distillate is referred to as the "hearts." This is the part of the distillate that can be consumed and used in production of spirits. Following ethanol, the end distillate is called the "tails" and is also an undesirable portion of the distillation because it contains higher alcohols and esters that can dull the character of the spirit (Berglund, 2004).
Image 1: 250 Gallon Column Still used at StillTheOne Distillery, Port Chester, New York. (Donnelly, 2012)
Image 2: Pot Still at Willett Distillery in Bardstown, Kentucky (Gardner, 2013)
Table 1: Boiling Points (°C) and Retention Times (minutes) for organic compounds in Fruit Eau-de-Vies
|Chemical name||Retention time (minutes)||Boiling point (C)|
|Isopentanol (isoamyl alcohol)||16.3||132.0|
Source: Claus and Berglund, 2005
Distilled wine is primarily used in the fortification of other alcoholic beverages. Brandy and port are examples of alcoholic beverages that use distilled wine in its production (Elias, 2012). Brandy is produced by distilling wine in a pot still or column still to 140-170 proof (70-85% alcohol), and is then aged in wooden barrels for a minimum of 2 years and up to 25 years (Elias, 2012). Port is produced by fermenting grape must to 15o Brix and fortifying with fortification brandy (brandy at roughly 185 proof) to halt the fermentation (Elias, 2012). In both products, the distilled grape/wine spirits are necessary to produce the final beverage product.
Faults in Wine
Wine faults can appear anywhere in the production process. Such faults include volatile acidity, oxidation, sulfur compounds, Brettanomyces contamination and cork taint.
Volatile Acidity (VA) refers to the volatile acids that are found in wines, which is primarily acetic acid. VA includes acetic acid (AA) and its breakdown product, ethyl acetate (EA). AA smells like vinegar while EA smells like nail polish remover. AA is regulated in wines, and maximum concentrations of 1.2 g/L in white wines and 1.4 g/L in red wines are deemed unacceptable. EA has a lower threshold (in mg/L range) than AA (in g/L range), but can be tolerated in very small concentrations (Gardner, 2013). VA is a production problem associated with acetic acid bacteria contamination, poor oxygen management, lack of sulfur dioxide maintenance and sour rot infection (Gardner, 2013).
Oxidation of wine is caused by oxygen exposure and carried through enzymatically or chemically (Gardner, 2013). A byproduct of wine oxidation is acetylaldehyde. The presence of acetylaldehyde smells like sherry or bruised apples, but it also reduces the perception of freshness and fruitiness of the wine. Production practices that contribute to oxygen in wine include pump overs, transfer operations, headspace in tanks and barrels, mixing, filtration, and bottling (Gardner, 2013).
Sulfur containing compounds are considered faults in wines when present at high levels. High levels of sulfur dioxide, hydrogen sulfide and mercaptans/thiols are sulfur containing compounds that can be present in faulted wines (Gardner, 2013). Sulfur dioxide is added to wines on a regular basis as an antioxidant and to promote freshness (Elias, 2012). Excess addition of sulfur dioxide results in high concentrations, masking fruitiness of the wine and may cause nasal irritation (Gardner, 2013). Hydrogen sulfide, which smells like rotten eggs, has a very low threshold and, therefore, must be regulated closely. When concentrations are higher than 1 ppb, freshness and fruitiness become compromised. Mercaptans and thiols also have a very low threshold and may mask fruity flavors in the wine, as well as contribute to their own associated off-aromas (Gardner, 2013).
Brettanomyces (Brett) is a spoilage yeast that can be considered a fault in wines when it overpowers the wine variety or style, especially when it is present in addition to other faults (Gardner, 2013). Brett has aromas that include that of a barn, horse, wet dog, leather and tobacco (Bisson, 2013) among others. Brett is typically caused by the use of old barrels, improper sanitation of barrels, cross contamination and the use of wood products in the winery (Gardner, 2013).
Cork taint is a musty aroma that results from the impact compound 2,4,6-Trichloroanisole (TCA). TCA is formed in wine when wine comes in contact with natural cork products in addition to chlorine (Elias, 2012). The threshold for TCA in wine is 1 part per trillion (ppt), so extremely low levels of this compound in wine will reduce flavor and aromas in wine (Gardner, 2013). At higher concentrations, TCA smells like wet cardboard or a dank musty cellar.
Distillation of Wine for Wine Fault Remediation
Distillation is used to produce many types of spirits, but in the wine industry, distilled wine can be used to produce brandy and port. Although the base beverage determines the neutrality and flavor of the distilled spirit, distillation can also be used to remediate some wine defects. The remainder of this paper will examine how faulted wine can be distilled for use in the wine industry.
Volatile Acidity is typically present in wine in the form of acetic acid (AA) and ethyl acetate (EA). AA has a boiling point of 118°C and EA has a boiling point of 77°C (Claus and Berglund, 2005). Recall that ethanol typically boils at 78.5°C (Claus, M). Through careful distillation techniques (i.e. manipulation of distillation temperatures), it is feasible to remove the ethanol from a high VA wine without retaining the AA and EA flaws in the distillate.
This principle can also be applied to oxidized wines, because oxidation as a fault is commonly seen alongside VA. Acetylaldehyde, the impact compound that is associated with oxidation, (Gardner, 2013) has a boiling point of 20.8°C. Therefore, acetylaldehyde be separated from ethanol through coarse or fine distillation and manipulation of temperature (Claus and Berglund, 2005).
Sulfur containing compounds, including hydrogen sulfide, sulfur dioxide and mercaptans/thiols, can have negative effects on distillates and may not be removed by distillation alone. Hydrogen sulfide can react with ethanol to produce ethyl mercaptan. This indicates that the hydrogen sulfide odor may be retained in the distillate (Berglund, 2004). However, many (but not all) sulfide containing compounds may be removed from faulted wine with the addition of copper. If copper stills are being used in the distillation of wine (which is very common), then excess sulfur containing compounds may be removed during the distillation process (Elias, 2012). Caution, however, should be taken by the winemaker.
Brettanomyces identification and remediation can be monitored by the presence or absence of 4-ethyl guaiacol (4EG) and 4-ethyl phenol (4EP) (Gardner, 2013). Lehtonen (1982) has suggested that 4EG will remain present in the hearts of the distillate in whiskey production. It was found that 4EG concentrations in whiskey exceeded odor thresholds (Lehtonen, 1982). These studies suggest that it would be difficult to remove the impact compounds associated with Brettanomyces contamination from distilled wine.
The impact compound of cork taint, 2,4,6-Trichloroanisole (TCA), has a boiling point of 132°C, which is well above the boiling point of ethanol and water (Sigma-Aldrich). This would initially suggest that the compound can be separated from ethanol through distillation practices. However, due to TCA's low threshold (1 ppt), it is possible to retain such concentrations in the distillate, hence leaving the concentrated ethanol product contaminated.
Distillation of wine for the remediation of wine faults offers production choices for winemakers. When faults occur in wine, it is ideal to rework the product rather than to throw the product away at an economical loss. The identification of wine faults is necessary first before remediation techniques can be applied.
With careful distillation techniques and understanding of the separation of compounds found in wine, ethanol can be separated effectively from less desirable compounds found in the faulted wine. The distillate produced from less than desirable wine can then be used to produce other wine based products including brandy and port style wine. Such practices offer an effective solution for reworking product that is not suitable for sale on its own as a faulted wine.
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Special thank you to Dr. Roger Boulton, Scott Professor of Enology, Viticulture and Enology Department, University of California, Davis for assisting with research with regards to this paper.
Prepared by Erin Donnelly, Penn State Food Science Undergraduate