Chapter 7
Brettanomyces and Dekkera Implications in Wine Making K. C. Fugelsang, M. M. Osborn, and C. J. Muller
Downloaded by COLUMBIA UNIV on June 14, 2013 | http://pubs.acs.org Publication Date: August 23, 1993 | doi: 10.1021/bk-1993-0536.ch007
Department of Enology, Food Science, and Nutrition and Viticulture and Enology Research Center, California State University, Fresno, CA 93740-0089
Yeasts of the genera Brettanomyces and Dekkera pose a serious threat to premium wine production. It has been conservatively estimated that annual economic losses resulting from their growth run into the hundreds of thousands of d o l l a r s . The h i s t o r i c a l l y ascribed habitat for both yeasts i s barrel-aging red wine. Research presented here points to the potential for significant a c t i v i t y during fermentation. Fermentative phase growth not only results in formation of objectionable metabolites that develop and intensify during aging, but also negatively impacts a c t i v i t y of the wine yeast Saccharomyces. Efforts should be directed toward exclusion of the organism and i n the case of already established infections, monitoring, isolation and control. Despite v a l i d concerns regarding "Brett"-growth in wine, some creative winemakers are currently exploring and advocating selective and controlled u t i l i z a t i o n of these yeasts as s t y l i s t i c tools. Background The process of winemaking, from v i n e y a r d t o b o t t l e d product, r e f l e c t s not only the unique c o n t r i b u t i o n o f t h e grapes and winemaker, but the combined a c t i v i t i e s o f r e s i d e n t v i n e y a r d and winery f l o r a as w e l l . Indeed, i f t h e process were not c o n t r o l l e d , we would see a s u c c e s s i o n o f m i c r o b i a l populations ( i n c l u d i n g both yeast and b a c t e r i a ) r e p r e s e n t i n g , i n i t i a l l y , those species present on the f r u i t and later those species t o l e r a n t of higher a l c o h o l environments. H i s t o r i c a l l y , winemaking has r e l i e d upon mixed c u l t u r e fermentations resulting from a succession of yeast 0097-6156/93/0536-0110S06.00/0 © 1993 American Chemical Society
In Beer and Wine Production; Gump, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
7. FUGELSANG ET AL.
Brettanomyces and Dekkera
p o p u l a t i o n s p o t e n t i a l l y r e p r e s e n t i n g s e v e r a l genera. Such fermentations are i n i t i a t e d by weakly fermentative s p e c i e s which are r e l a t i v e l y a l c o h o l s e n s i t i v e . These are q u i c k l y overgrown by strongly fermentative strains of Saccharomyces. The d e t a i l s regarding i d e n t i f i c a t i o n and enumeration of n a t i v e yeasts can be found i n various r e p o r t s (15, 21, 23). D i s t r i b u t i o n and p o p u l a t i o n d e n s i t i e s of n a t i v e species vary widely, reflecting environmental and v i t i c u l t u r a l f a c t o r s as w e l l as maturity and i n t e g r i t y of the f r u i t . Reed and Nagodawithana (23), c i t i n g French r e s e a r c h , r e p o r t yeast c e l l counts ranging from l e s s than 160 t o 10 CFU/berry. Worldwide, the most f r e q u e n t l y i s o l a t e d n a t i v e yeasts are Hanseniaspora uvarum and i t s asexual or "imperfect" counterpart Kloeckera apiculata. Other common n a t i v e yeasts are Metschnikowia pulcherrima and i t s imperfect form, Candida pulcherrima (23). Yeasts i s o l a t e d l e s s f r e q u e n t l y i n c l u d e Torulopsis delbrueckeii, Hansenula anomala, and Pichia membranefaciens. Saccharomyces sp. are i n f r e q u e n t l y i s o l a t e d from vineyards where winery wastes are not r e i n c o r p o r a t e d as soil amendments. In instances where such p r a c t i c e s are u t i l i z e d , r e s i d e n t populations may be h i g h . Pardo e t . a l . , (17) r e p o r t l e v e l s as high as 5 χ 10* CFU i n Spanish grape musts. These same workers a l s o r e p o r t incoming musts where Saccharomyces was not i s o l a t e d , suggesting considerable habitat v a r i a b i l i t y . In C a l i f o r n i a , there i s renewed i n t e r e s t among some winemakers i n n a t i v e yeast fermentation. However, i t i s our opinion that, aside from isolated locales where v i t i c u l t u r a l practices a r t i f i c i a l l y create a microbial community with r e l a t i v e l y high p o p u l a t i o n d e n s i t y of Saccharomyces, n a t i v e vineyard yeasts represent s p e c i e s t h a t are, with few exceptions, i l l s u i t e d f o r winemaking. At best, most of the " w i l d " yeast f l o r a i s represented by weak fermenters, capable of producing only 4-5% a l c o h o l , concomitant with a v a r i e t y of unpleasant m e t a b o l i t e s . F o r t u n a t e l y f o r winemakers (past and present) working under these c o n d i t i o n s , one or more s t r a i n s of more s t r o n g l y fermentative and a l c o h o l t o l e r a n t Saccharomyces e v e n t u a l l y predominates and completes fermentation (42). E a r l y v i n t n e r s recognized the importance of y e a s t i n fermentation and made conscious e f f o r t s t o propagate those s t r a i n s they b e l i e v e d important i n the process. The extent of t h e i r e f f o r t s no doubt v a r i e d with s c i e n t i f i c awareness, ranging from plowing fermented pomace back i n t o the v i n e y a r d t o maintenance of pure c u l t u r e s t r a i n s i n the winery l a b o r a t o r y . Needless t o say, product u n i f o r m i t y represented a s e r i o u s problem t o e a r l y winemakers and most of the w o r l d s wine was l i k e l y produced more by f o r t u i t o u s circumstance than i n t e n t i o n a l d i r e c t i o n . With a b e t t e r understanding of the elements i n v o l v e d i n fermentation as w e l l as the technology f o r implementation and manipulation, winemakers i n the l a s t century (and p a r t i c u l a r l y the l a s t 50 years) have gained a greater c o n t r o l over the onset and 5
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In Beer and Wine Production; Gump, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
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BEER AND WINE PRODUCTION
outcome of fermentation as w e l l as c e l l a r i n g and b o t t l i n g wine. To produce a c o n s i s t e n t l y s u p e r i o r product on a g l o b a l b a s i s , winemakers needed yeasts with r e l a t i v e l y uniform and p r e d i c t a b l e m i c r o b i o l o g i c a l p r o p e r t i e s . C h i e f among these was s u s t a i n a b l e v i a b i l i t y over the course of fermentation. T h i s r e q u i r e d the a b i l i t y t o grow i n the low pH (
