Sources of acetic and other fatty acids and their role in sluggish or stuck fermentations


Project Number
IWBT 01-11

Project title
Sources of acetic and other fatty acids and their role in sluggish or stuck fermentations

Project leader
Du Toit, M A

Institution
University of Stellenbosch. Department of Viticulture and Enology. Institute for Wine Biotechnology

Team members
Du Toit, W J
Lambrechts, M G
Oelofse, A
Downing, L

Project description
To determine whether acetic acid bacteria, lactic acid bacteria, non-Saccharomyces yeasts or commercial wine yeasts are responsible for the above average acetic acid production in some red wine fermentations.

To advise the industry on the prevention of acetic acid production.

Incomplete or stuck fermentations are often experienced during red winemaking. These wines often contain high levels of volatile acidity, which is detrimental to wine quality. The source(s) of these high acetic acid levels are unknown, as well as the role which acetic acid may play in the onset of a stuck fermentation. Numerous micro-organisms can contribute to high levels of volatile acidity. Acetic acid bacteria produce acetic acid and ethyl acetate from sugar as well as ethanol in the presence of oxygen. Lactic acid bacteria can also produce acetic acid. Lactobacillus can be homofermentative (more than 85% lactic acid produced) or heterofermentative [lactic acid, carbon dioxide and ethanol (and/or acetic acid) produced in equimolar quantities]. Larger quantities of acetic acid would thus be produced in the presence of oxygen or any other oxidant instead of lactic acid and ethanol. Leuconostoc is heterofermentative and can also produce more acetate in the presence of oxygen. Certain Pediococcus species also form equimolar quantities of lactic and acetic acid from pentose sugars. Literature states that acetic and lactic acid bacteria produce acetic acid at the beginning of fermentation.

Certain wild yeasts, such as Brettanomyces, Hansenula anomala, Kloeckera apiculata and Candida krusei can produce high levels of acetic acid. These yeasts can occur in high numbers on the grapes, during fermentation and even in inoculated fermentations. Dry warm seasons might result in higher than normal amounts of these yeasts on grapes and could therefore be responsible for the high levels of acetic acid.

Commercial wine yeasts can also produce higher levels of acetic acid under certain conditions. These levels are influenced by the nitrogen source, sugar concentration and the pH. Higher levels of acetic acid are normally produced under growth-limiting conditions and also at sugar concentrations over 20%. The influence of the nitrogen differs according to its source. Certain compounds (ammonium, glutamate, asparagine) inhibit the production of acetic acid when an ample supply of nitrogen is present whilst others such as methionine and valine can enhance the production of acetic acid. When the available nitrogen is inadequate, higher concentrations of acetate are produced at higher sugar concentrations. At pH values lower than 3.2 and higher than 4, more acetic acid is formed.

No research has been done on the origin and sources of the high levels of acetic acid in South African wines. We believe that this research could provide answers to the short as well as long term problems being experienced annually with stuck fermentations and high levels of volatile acidity in red winemaking.

Presentation(s)
Lambrechts, M G, Du Toit, W J and Ellis, L E. 1998. Microbiology of South African red wine fermentations and colour extraction. Presentation to the Pinotage Society of South Africa, Stellenbosch.

Lambrechts, M G, Du Toit, W J and Ellis, L P. 1999. The occurrence and characterisation of acetic acid bacteria in commercial red wine fermentations. Paper presented at the 6th International Enological Symposium: OENO 99. 10-12 June, Bordeaux, France.

Du Toit, M A, Du Toit, W J, Lambrechts, M G and Ellis, P L. 1999. Acetic acid bacteria present in South African red wine fermentation and their characteristics. Paper presented at 17th International Conference of the International Committee on Food Microbiology and Hygiene. 13-17 September, Veldhoven, The Netherlands.

Lambrechts, M G, Du Toit, W J and Ellis, L E. 1999. The occurrence and characterisation of acetic acid bacteria in commercial red wine fermentations. Paper presented at the 23rd National Congress of the South African Society for Enology and Viticulture. 12-13 November, Cape Town, South Africa.

Bayly, J C, Du Toit, W J, Du Toit, M A, Lambrechts, M G and Pretorius, I S. 2000. The isolation, identification and characterisation of lactic acid bacteria during South African red wine fermentations. Paper presented at the 2nd International Congress of the South African Society for Enology and Viticulture. 8-10 November, Cape Town, South Africa.

Bayly, J C, Du Toit, W J, Du Toit, M A, Lambrechts, M G, Bergstedt, J K and Jolly, N P. 2000. Microbiological characterization of wines towards the development of volatile acidity. Paper presented at the 2nd International Congress of the South African Society for Enology and Viticulture. 8-10 November, Cape Town, South Africa.

Lambrechts, M G, Du Toit, W J and Ellis, L P. 2000. The occurrence and characterisation of acetic acid bacteria in commercial red wine fermentations. Paper presented at the 25th World Congress of Vine and Wine and the 80th General Assembly of the OIV. 19-23 June, Paris, France.

Bayly, J C, Du Toit, W J, Du Toit, M A and Lambrechts, M G. 2000. The isolation, identification and characterisation of lactic acid bacteria occurring during South African red wine fermentations. Paper presented at BIOY2K Combined Millennium Meeting. 23-28 January, Grahamstown, South Africa.

Du Toit, M A. 2001. Lactic acid bacteria and spoilage. Seminar on Wine bacteria: Winemakers friend or enemy? Lecture. University of Stellenbosch, Stellenbosch, South Africa.

Bergstedt, J K, Lambrechts, M G, Jolly, N P and Du Toit, M A. 2001. The influence of non-Saccharomyces yeast on volatile acidity in wines. Paper presented at the 25th National Congress of the South African Society for Enology and Viticulture.15-16 November, Cape Town, South Africa.

Ferreira, J, Du Toit, M A, Du Toit, W J and Pretorius, I S. 2002. The effect of different commercial wine yeast strains on bacterial counts during fermentation and their fermentation performance. Paper presented at the 26th National Congress of the South African Society for Enology and Viticulture. 13-15 November, Somerset West, South Africa.

Oelofse, A, Lambrechts, M G, Pretorius, I S and Du Toit, M A. 2003. Characterisation of wine isolated acetic acid bacteria from South African red wines. Paper presented at 1st FEMS Congress of European Microbiologists. 29 June ? 3 July, Ljubljana, Slovenia.

Article
Du Toit, W J, Ellis, L E, Lambrechts, M G. 1995. Bronne van asynsuur en ander vetsure in kommersiële rooiwyn fermentasies, Wynboer, Mnth Jan (p. 55)

Van der Westhuizen, T J, Augustyn, O P H, Pretorius, I S. 1999. The value of long-chain fatty acid analysis, randomly amplified polymorphic DNA and electrophoretic karyotyping for the characterisation of wine yeast strains, South African Journal of Enology and Viticulture, v. 20 (1) (p. 3-10)

Du Toit, W J. 2001. Die voorkoms van asynsuurbakterieë in Suid-Afrikaanse rooiwyn fermentasie, WineLand, Mnth May (p. 103-106)

Du Toit, W J. 2001. The sulphur dioxide resistance of South African acetic acid bacteria and their effect on fermentation, WineLand, Mnth Nov (p. 97-101)

Du Toit, W J. 2001. Winemaking with rotten grapes: it can be a headache, WineLand, Mnth Dec (p. 81-83)

Du Toit, W J, Pretorius, I S. 2002. The occurrence and esoteric effect of acetic acid bacteria in winemaking, Annals of Microbiology, v. 52 (p. 155-179)

Du Toit, W J, Pretorius, I S. 2002. The occurrence and esoteric effect of acetic acid bacteria in winemaking, Bulletin d’OIV, v. 75 (p. 284-302)

Du Toit, W J, Lambrechts, M G. 2002. The enumeration and identification of acetic acid bacteria from South African red wine fermentations, International Journal of Food Microbiology, v. 74 (p. 57-64)

FinalReport.pdf

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