Spoilage diacetyl formation

At low levels (5 mg/L), diacetyl is considered to add complexity to wine aroma since it can impart positive nutty or caramel characteristics, although at levels above 5 mg/L it can resuit in spoilage, creating an intense buttery or butterscotch flavour, and is perceived as a flaw. Microbial formation of diacetyl is a dynamic process and its concentration in wine depends on several factors bacterial strain, pH, wine contact with lees, SO2 content (Martineau and Henick-Kling 1995 Nielsen and Richelieu 1999). The sensory threshold for the compound can vary depending on the levels of certain wine components, such as sulfur dioxide. It can also be produced as a metabolite of citric acid when all the malic acid has been used up. However, diacetyl rarely taints wine to levels where it becomes undrinkable. 

Species Beer- spoilage ability Primary/ secondary contamination s Exopolysaccharide formation Diacetyl production Culturability on MRS agar ... 

Fermentation. Fermentation processes in general play an important role in determining the precise flavour of the final product. During fermentation, spoilage microorganisms may proliferate, leading to the formation of volatiles, such as acetaldehyde, diacetyl, various sulphur... 

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