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52 practical winery & vineyard March 2015 glycerol, which prevents the movement of water from the yeast cell into the must. Glycerol is formed through a NADH-dependent enzy- matic reaction. The subse- quent conversion of NADH to NAD+ changes the redox bal- ance, which is corrected for byproduction of acetic acid, shifting the redox potential back to equilibrium. 3 This results in excessive levels of acetic acid. P. Giudici and C. Zambonelli suggest that perhaps the rea- son for acetic acid production by yeast in normal table wines is due to acetic acid's role as an intermediate in the forma- tion of acetyl coenzyme A from acetaldehyde. 4 However, R. Boulton states that a con- sensus has not been reached concerning the mechanism of the enzymatic formation of acetic acid. 1 A typical VA of an unspoiled wine is around 200 to 400 ppm. 8 There is no given "threshold of detec- tion" for VA. The perception of these compounds can dif- fer between wines, since high W I N E m A k I N G Vola le fa y acids in wine: The short- and medium-chain fa y acids are the most studied fa y acids in wine and are responsible for what is known as vola le acidity (VA). VA is a measure of all the steam-dis llable vola le acids present in wine. These can include ace c, lac c, formic, butyric and propionic acid. Other organic acids, excep ng ace c acid, are of li le consequence to wine flavor and aroma. Sulfur compounds in wine: Vola le sulfur compounds, such as thiols, are responsible for the ripe/fruity aromas of Sauvignon Blanc and are formed during fermenta on. They can also contribute a box-tree-like aroma in Sauvignon Blanc. Further, sulfurous compounds at low concentra ons may cause a perceived "minerality" in some wines. Graver Technologies has been designing and producing superior ltration, separation and puri cation solutions for more than 100 years. Discover why Graver Technologies is the Clear Choice for beverage manufacturers around the globe. • Clarity • Stability • Taste • Consistency • E ciency • Economy • Reliability 200 Lake Drive, Glasgow, Delaware 19702 Phone: 302-731-1700 Website: www.gravertech.com E-Mail: info@gravertech.com Discover The Clear Choice Quality | Performance | Value Practical Winery BOOKSHelF Your source for informative, technical books practicalwinery.com. Click BOOKSHELF C h e m i c a l a n a l y s i s o f g r a p e s a n d w i n e : t e c h n i q u e s a n d c o n c e p t s P a t r i c k I L A N D , N i c k B R U E R , G r e g E D W A R D S , S u e W E E K S a n d E r i c W I L K E S Monitoring the winemaking process from grapes to wine techniques and concepts P a t r i c k I L A N D , N i c k B R U E R , A n d r e w E W A R T , A n d r e w M A R K I D E S a n d J o h n S I T T E R S