Successful winemaking uses selected wine microorganisms to convert fruit flavours into wine flavours. These grape varietal and regional wine flavours can be partially or even totally obscured by wine spoilage yeast and bacteria. Potentially most damaging are apiculate yeasts like Kloeckera/Hanseniaspora spp. and Brettanomyces/Dekkera bruxellensis. Avoiding microbial wine spoilage starts with selecting fruit that is unbroken and free of mould infection and it continues by managing temperature, pH, and winery sanitation throughout the winemaking process. This paper focuses on the introduction of spoilage microorganisms with the grapes, in particular apiculate yeasts with grapes that are affected by diffuse powdery mildew infection and on the control of Brettanomyces yeast from grape maceration to barrel ageing. It is well known that grapes with visible fungal infections (Botrytis, powdery mildew, and others) carry a much higher microbial load into the start of fermentation than grapes with are unbroken by insects, birds, or fungal hyphae. Such damaged fruit can carry more than several million viable yeast and bacteria per mL compared to sound fruit, which carries less than several thousand yeast and bacteria. Also, the types of microorganisms carried by damaged fruit are very different from those on undamaged fruit. Most of the microorganisms carried on sound fruit does not survive the juice and early fermentation stage while the oxidative yeast and bacteria in damaged fruit can survive throughout the wine fermentation and even be carried into the wine ageing stage. A study of the easily overlooked diffuse infection of powdery mildew showed a very large population of apiculate yeasts in the grape must of such infected grapes that appear undamaged. These potent spoilage yeast must be suppressed by heavy juice fining and possibly juice pasteurisation. Pre-fermentation time must be kept very short and the temperatures between 5 and 15°C must be avoided. The addition of yeast and bacteria starter cultures also helps to suppress these spoilage yeasts. The feared wine spoilage yeast Brettanomyces bruxellensis can also get established in a vineyard and in early stages of vinification such as cold maceration and sluggish onset of alcoholic fermentation. The next critical stage for proliferation of Brettanomyces is during delayed malolactic fermentation. When, following completion of alcoholic fermentation, the wine is not protected by active malolactic bacteria or by pH control and addition of SO2 it is critically exposed to spoilage by Brettanomyces. During wine ageing, the wine must be protected against Brettanomyces contamination from the barrel surface and winery environment. Strategies to suppress growth of Brettanomyces will be presented.
|Title of host publication||Thirteenth Australian Wine Industry Technical Conference|
|Editors||R.J. Blair, P.J. Williams, I.S. Pretorius|
|Place of Publication||Urrbrae, South Australia|
|Publisher||Australian Wine Industry Technical Conference Inc.|
|Number of pages||4|
|Publication status||Published - 2007|
|Event||Australian Wine Industry Technical Conference - Adelaide, Australia, Australia|
Duration: 28 Jul 2007 → 02 Aug 2007
|Conference||Australian Wine Industry Technical Conference|
|Period||28/07/07 → 02/08/07|
Henick-Kling, T., & Conterno, L. (2007). Avoiding microbiological wine spoilage. In R. J. Blair, P. J. Williams, & I. S. Pretorius (Eds.), Thirteenth Australian Wine Industry Technical Conference (pp. 65-68). Australian Wine Industry Technical Conference Inc..