Acid degradation
Acid degradation refers to the reduction of organic acids in grapes and wine through biochemical, microbiological and chemical processes occurring during grape ripening, fermentation and ageing. It plays a central role in determining wine balance, softness, microbial stability and ageing potential, and is closely linked to malolactic fermentation and climatic conditions.[1]
Acid metabolism in grapes
In grapes, acid degradation occurs primarily through the respiration of malic acid during ripening. As temperatures increase, malic acid is consumed as an energy source, leading to declining total acidity and rising pH.[2]
This process is strongly temperature-dependent and accelerates in warm climates, late harvest situations and during heatwaves, contributing to lower natural acidity at harvest.[3]
Malolactic fermentation
The most significant form of acid degradation in winemaking is malolactic fermentation, during which malic acid is converted into lactic acid and carbon dioxide by lactic acid bacteria. This transformation reduces total acidity and softens the sensory perception of wine.[4]
Malolactic fermentation also alters aroma and mouthfeel, often contributing buttery, creamy or nutty notes and increased microbiological stability.[5][6]
Winemaking control
Winemakers may encourage, delay or suppress acid degradation depending on wine style, grape variety and regional tradition. Temperature management, sulphur dioxide use, filtration and bacterial inoculation are common tools used to control malolactic fermentation.[7]
In some styles, particularly aromatic whites and sparkling base wines, limiting acid degradation is essential to preserve freshness and structural tension.[8]
Sensory and chemical implications
Acid degradation leads to higher pH and lower titratable acidity, influencing colour stability, oxidation rate and microbial risk. Wines with excessive acid loss may appear flat, dull or unstable over time.[9]
Conversely, controlled acid degradation can enhance balance and approachability, particularly in high-acid grapes or cool-climate wines.[10]
Climate change effects
Rising temperatures have intensified acid degradation trends globally, increasing the challenge of maintaining freshness and typicity in many wine regions. Earlier harvests, site selection and altered winemaking practices are increasingly used to counteract accelerated acid loss.[11]
These shifts have contributed to evolving stylistic norms and regulatory discussions around acidity management and balance.[12]
Institutional guidance
International and academic bodies provide guidelines and research on acid degradation and malolactic fermentation to support quality control and stylistic consistency across regions.[13][14][15][16]
See also
References
- ↑ Robinson (ed.), The Oxford Companion to Wine, Oxford University Press, 2015, ISBN 9780198705383.
- ↑ Keller, The Science of Grapevines, Academic Press, 2015, ISBN 9780124199873.
- ↑ Jackson, Wine Science: Principles and Applications, Academic Press, 2020, ISBN 9780128161180.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Volume 1, Wiley, 2006, ISBN 9780470010372.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Volume 2, Wiley, 2006, ISBN 9780470010396.
- ↑ Stevenson, The Sotheby’s Wine Encyclopedia, DK, 2011, ISBN 9780756686840.
- ↑ Boulton et al., Principles and Practices of Winemaking, Springer, 1999, ISBN 9780834217011.
- ↑ Peynaud, Knowing and Making Wine, Wiley, 1984, ISBN 9780471881491.
- ↑ Waterhouse, Sacks & Jeffery, Understanding Wine Chemistry, Wiley, 2016, ISBN 9781118627808.
- ↑ Stevenson, The Sotheby’s Wine Encyclopedia, DK, 2011, ISBN 9780756686840.
- ↑ Jones et al., Climate Change and Global Wine Quality, Wiley, 2012, ISBN 9781118450048.
- ↑ Anderson & Pinilla, Wine Globalization, Cambridge University Press, 2018, ISBN 9781108445687.
- ↑ OIV, “Malolactic fermentation and acid management”, https://www.oiv.int
- ↑ UC Davis, “Malic acid degradation”, https://wineserver.ucdavis.edu
- ↑ AWRI, “Managing malolactic fermentation”, https://www.awri.com.au
- ↑ FAO, “Wine fermentation processes”, https://www.fao.org