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72 P R A C T I C A L W I N E R Y & V I N E YA R D August 2015 W I N E M A K I N G temperatures, the encouragement of an aerobic environment, excessive turbid- ity within the must, chaptalization and fermenting within pressure tanks all encourage the production of higher alco- hol. An increased pH will also result in larger amounts of fusel alcohols. Conversely, the addition of SO 2 sup- presses fusel alcohols. 25 The concentrations at which yeast form higher alcohols is dependent upon the genus, species and strain. Although yeast manufacturers claim their strains pro- duce fusel alcohol, this may not be of consequence to the winemaker. The level of higher alcohol is generally so low in table wine that it is unnoticed; a concen- tration high enough for perception may be found off-putting. 3 Regardless, studies show the strain of yeast significantly impacts the amount of higher alcohol produced. 1,17 T. Herraiz et al. noted a marked difference in higher alcohol production among apiculate yeast when compared to S. cerivisiae. 10 Yeast that carry out a portion of alco- holic fermentation (such as Kluyveromyces thermotolerans) produce more fusel alco- hols than the more robust fermenters such as Schizosaccharomyces pombe. This suggests more fusel alcohols are found in wines produced from wild fermenta- tions. Similarly, the same is likely true in wines where the commercial yeast used includes a blend of a non-Saccharomyces species, which partly ferments the must before the fermentation is taken over by a Saccharomyces strain. 3 Volatile phenols We normally think of phenolics as major contributors to a wine's mouthfeel and color. However, the phenolics in the grape are a source of hydrocinnamic acid esters. These esters, most impor- tantly ferulic and coumaric acid esters, can be synthesized into volatile phenols by yeast. There are two "classes" of phenols. There are the vinylphenols (4-vinylphe- nol [4-VP] and 4-vinylguaiacol [4-VG]), which are found in white wines, and there are the more commonly discussed ethylphenols (4-ethylphenol [4-EP] and 4-ethylguaiacol [4-EG]), which are found in red wines. These compounds are found at low concentrations and have a very low sensory threshold. Volatile phenols are associated with aromas described most commonly as "medicinal," "barnyard," "sweat" and "animal." The most common culprit of the production of these compounds is the Brettanomyces and Dekkera species of yeast. 18 However, it should be noted that 4-vinylguaiacol is not always consid- ered a fault, as in Gewürztraminer it is associated with clove/spicy aroma; 4-vinylphenol is responsible for a car- nation-like aroma in Gewürztraminer. 22 This component of the varietal aroma of Gewürztraminer is likely due to an unusually high quantity of ferulic and coumaric acids present in the juice of this variety. The volatile phenols are always found together in wine (a wine with 4-VP will also have 4-VG). The sensory threshold for the combination of vinyl-phenols is more than twice that of the ethyl-phenols (Table 1). Volatile phenols are microbial-derived products formed from odorless precur- sors that are present in all grapes (ferulic and coumaric acids). It was assumed that lactic acid bacteria were culprits for the production of off volatile phenol aromas in wines. However, it has been demonstrated that off-phenol aromas are more likely to arise from Brettanomyces/ Dekkera. 6 SCREW Making the move to screw cap? Want to run roll-on and torque-on with the same machine? Arol's flexible capping technology applies everything from corks, to torque-on aluminum closures. With over thirty years' experience and 15,000 machines to-date, we have a perfect solution for your application. We custom design your machine for your specific application. Contact us at: AROL North America 450 Satellite Blvd NE | Suite A Suwanee, GA 30024 | Tel: 678.318.1290 www.arol.com WV201111_arol_island.indd 1 11/4/2011 9:05:39 AM