Refermentation
Refermentation refers to the renewed fermentation of sugars in wine after the primary alcoholic fermentation has been considered complete. It may occur intentionally, as in the production of certain sparkling or sweet wines, or unintentionally, where it is generally regarded as a wine fault due to its impact on stability, clarity and sensory quality.[1]
Definition and context
Refermentation involves the metabolic activity of yeasts or, less commonly, bacteria that resume converting fermentable sugars into ethanol and carbon dioxide. In most still wines, this process is unintended and arises when residual sugars remain in the wine and viable microorganisms survive bottling or storage.[2]
In contrast, refermentation is deliberately induced in specific winemaking contexts, most notably in traditional-method sparkling wines and some sweet wines where fermentation is arrested and later restarted under controlled conditions.
Causes
Unintended refermentation is typically associated with one or more of the following factors:
- residual fermentable sugars
- insufficient microbiological stability
- inadequate filtration or sterilisation prior to bottling
- contamination with fermentative yeasts after bottling
Yeast species involved may include Saccharomyces cerevisiae, but spoilage yeasts such as Zygosaccharomyces are also frequently implicated due to their high tolerance to alcohol and sulphur dioxide.[3]
Sensory and physical effects
Refermentation in bottle or tank can lead to turbidity, sediment formation and the development of unwanted carbon dioxide pressure. Sensory effects may include spritziness, sweetness imbalance, yeasty or bread-like aromas and, in severe cases, bottle leakage or breakage.[4]
Even minor refermentation can be considered a quality defect in wines expected to be microbiologically stable and still.
Intentional refermentation
In some wine styles, refermentation is a fundamental part of production. Examples include traditional-method sparkling wines, where a secondary fermentation in bottle generates carbon dioxide, and certain aromatic or sweet wines where fermentation may resume after bottling under controlled conditions.[5]
In these cases, refermentation is carefully managed through yeast selection, temperature control and pressure monitoring.
Prevention and control
Preventing unintended refermentation relies on a combination of analytical, microbiological and technological measures. These include complete fermentation to dryness where appropriate, sterile filtration, sulphur dioxide management and rigorous hygiene during bottling.[6]
Modern wineries may also employ microbiological testing and membrane filtration to ensure stability prior to release.
Regulatory and market considerations
Refermentation can have commercial and regulatory implications, particularly where pressure build-up poses safety risks or where wine styles fail to meet legal definitions. Consumer perception of refermentation in still wines is generally negative, associating it with poor quality or spoilage.[7]
See also
References
- ↑ Jancis Robinson, Oxford Companion to Wine, Oxford University Press, 17 Sept. 2015. ISBN 9780198705383.
- ↑ PhD Jackson, Ronald S., Wine Science: Principles and Applications, Academic Press Inc, 14 April 2020. ISBN 9780128161180.
- ↑ Kenneth C. Fugelsang, Wine Microbiology, Springer, July 31, 1997. ISBN 9780412066115.
- ↑ Lawless, Wine Faults, Mitchell Beazley, 2013, ISBN 9781845337233.
- ↑ Roger B. Boulton, Vernon L. Singleton, Linda F. Bisson, Ralph E. Kunkee, & 1 more, Principles and Practices of Winemaking, Springer, 31 Oct. 1998. ISBN 9780834212701.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Vol. 2, Wiley, 2006, ISBN 9780470010396.
- ↑ Charters, Wine and Society, Elsevier, 2006, ISBN 9780750669788.