Wines & Vines

March 2015 practical winery & vineyard 51 V olatile acidity and hydrogen sulfide are nearly unanimously classified as wine faults by vintners. Some sulfurous com- pounds can be pleasant, as is the case with grape-derived thiols that are intrin- sic to the passion fruit, box wood and grapefruit aromas of Sauvignon Blanc. However the sulfurous compounds that are purely derived from yeast are not considered valuable to the vintner. The volatile fatty acids are likely only considered to be contributors of positive aromas by those who produce vinegar. In wine, volatile fatty acids are responsible for a major fault when they accumulate beyond their sensory threshold. Volatile fatty acids The volatile fatty acids found in wine consist primarily of short-chain fatty acids (tails of less than six carbons) and medium-chain fatty acids (tails with six to 12 carbons). The short- and medium- chain fatty acids are the most studied fatty acids in wine and are responsible for volatile acidity (VA). VA is a measure of all the steam-distill- able volatile acids present in wine. These can include acetic, lactic, formic, butyric and propionic acid. 15 Other organic acids, excepting acetic acid, are of little conse- quence to wine flavor and aroma. About 90% of all the volatile acidity in wine comes from acetic acid, which, in con- junction with ethyl acetate, possesses a vinegar-like aroma. 8 Yeast produce acetic acid during fer- mentation within the range of 100 to 200 mg/L, depending on the yeast strain and vigor of fermentation (temperature and juice nutrient status). 1 This usually occurs during the beginning lag phase of fermentation. 14 However, excessive acetic acid production is usually an indicator of microbial spoilage by Acetobacter and Gluconobacter. 1 Acetic acid from microbial sources is derived through various pathways. One mode is through the degradation of sug- ars by lactic acid bacteria via the phos- phoketolase process (the way in which bacteria can break down residual sugar). Alternatively, acetic acid can simply be produced as part of the citric acid cycle. Acetobacter and Gluconobacter can oxidize ethanol to acetic acid enzymatically with alcohol dehydrogenase (first oxidized to acetaldehyde then to acetate with alde- hyde dehydrogenase). 10 Acetic acid (high VA) is a common issue when creating ice wines. Under ice wine conditions, the yeast are under high osmotic stress. In order to adapt to this condition, yeast cells will exude W I N E m A k I N G Russell Moss BY This ar cle is part of a series that covers the fungal and bacterial origins of wine aromas. These ar cles detail esters, aldehydes, vola le fa y acids, sulfurous compounds, vola le phenols and higher alcohols. The old adage "one man's trash is another man's treasure" holds true with most of these compounds. Microbial origins of key wine aromas VOL ATILE FATTY ACIDS and SULFUROUS COMPOUNDS Toll-Free: 877-552-4828 909-464-1373 • Fax: 909-464-1603 For your nearest dealer, contact: BRANCHLOK™ Used for lateral training of trellised branches and cordons to 12-14 gauge wire. Branchlok™ is available in three lengths: 2½", 3¼", 3 ¾". Patent No. 4,665,000 WineVineBranchLokAD.qxp_Layout 1 12/1/14 2:46 Visit us at miovigneto.com Email: dwightb@miovigneto.com Call Dwight Busalacchi at (415) 531-6450 CIP Balls & Adaptors Custom Tanks & Fermentors Horizontal Membrane Presses Slovenian Oak Barrels & Casks "Excellent quality at reasonable prices with exceptional customer service built around an understanding of vintners' needs." ~ Jim Schultz, Windy Oaks Winery Mio Vigneto Products, Inc. Outstanding Tanks for Outstanding Wines

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