Sunday, July 8, 2012

FWWS Blog for July 8, 2012 Introducing "Techbits" New service for FWWS members

Dear FWWS Member,

We at the Board are attentive to input from Members. One of the comments we have heard repeatedly is that our blog posts are sometimes too lengthy to easily digest. We regret that some of the issues that face our industry are unfortunately complex but nevertheless vitally important for our members to understand. We are doing our best in this regard to reduce issue fatigue.

Thinking about this constructive criticism highlighted another facet of our industry that we as fellow winemakers recognize, namely the wealth, sometimes overabundance, of technical information available to winemakers who are often too busy to attend seminars or keep up with journal articles. In the hopes that we can add a useful feature of membership in FWWS, we are inaugurating a new service to members to provide a condensed digest of technical information in enology. The first edition which follows summarizes a very interesting article on acetaldehyde, an important factor in wine quality. Your comments are on this new service are greatly appreciated.

Your FWWS Board

Introducing "Techbits" - Tidbits of wine technical information gleaned from industry sources and summarized in bite-sized pieces. A benefit of membership in FWWS

Acetaldehyde formation and degradation in wine.

Acetaldehyde can be formed in wine either chemically (by oxidation of ethanol) or biologically (by fermentation). It is a highly reactive molecule typically having an apple-like, nutty, or green grass aroma. Sensory thresholds have been reported as between 0.5 and 10 mg/L for odor, and between 100 and 125 mg/L for flavor.

It is a misconception that the risk of formation of acetaldehyde begins at the end of alcoholic fermentation and in the absence of SO2. Given careful cellar operations limiting exposure of finished wine to oxygen during cellaring, most acetaldehyde formation will occur as a result of fermentation, particularly by Saccharomyces cerevisiae (non-Saccharomyces cerevisiae yeast typically produce much less acetaldehyde except for Schizosaccharomyces pombi, which also produces significant amounts). Most acetaldehyde is produced very early in fermentation. A significant amount of acetaldehyde is re-utilized by yeast during alcoholic fermentation, and a very significant amount – up to 94% - may be degraded by malolactic fermentation (MLF).

Residual concentration of acetaldehyde in wine is influenced by the following factors, which result in either higher creation of acetaldehyde during fermentation or lower utilization and degradation:

• Addition of SO2 to musts. Yeast produce more acetaldehyde in response to addition of SO2. Addition of 50 PPM SO2 to a must can increase the post alcoholic fermentation level of acetaldehyde by 10 to 25 mg/L. Since acetaldehyde is the most readily bound carbonyl compound in wine, this can also increase the bound SO2 concentration in wine by 15 to 37 mg/L.

• Anything increasing large viable concentrations of yeast during fermentation will lead to greater utilization of acetaldehyde and a reduction of its concentration in the wine post fermentation. These factors can include presence of yeast nutrients and maintenance of temperatures of 20 C.

• Consequently cooler temperatures (12 C or below), particularly in combination with poor yeast nutrient availability, can lead to higher residual acetaldehyde.

• Early racking and clarification of yeast can also increase residual acetaldehyde concentration by reducing utilization.

• MLF is the largest factor in the degradation of acetaldehyde in wine.

• In addition to increasing levels of acetaldehyde, large pre-fermentation SO2 additions also increase bound SO2 levels, which recent research shows have a significant adverse effect on malolactic bacteria (even in the absence of free SO2) and consequently on the reduction of acetaldehyde through degradation by MLF.

Source: “Role of Winemaking and Carbonyl Compounds” by Nick Jakowetz, Erhu Li, and Roman Mira De Orduna, Assoc. professor of Food Science, Cornell University. Published in Practical Winery and Vineyard Journal, Winter 2012.


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