Yeast: Difference between revisions

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'''Yeast''' (/jiːst/) are unicellular fungi of great importance in [[winemaking]], responsible for the alcoholic [[fermentation]] that transforms [[grape must]] into [[wine]]. The term derives from Old English ''gist'' and Proto-Germanic roots meaning "foam" or "boil", reflecting the frothing effect of fermentation. The most significant species in [[oenology]] is ''[[Saccharomyces cerevisiae]]'', though other genera also contribute to fermentation under certain conditions.<ref>Robinson ~~(ed.)~~, ''~~The~~ Oxford Companion to Wine'', Oxford University Press, 2015, ISBN ~~978-0198705383~~.</ref>

'''Yeast''' (/jiːst/) are unicellular fungi of great importance in [[winemaking]], responsible for the alcoholic [[fermentation]] that transforms [[grape must]] into [[wine]]. The term derives from Old English ''gist'' and Proto-Germanic roots meaning "foam" or "boil", reflecting the frothing effect of fermentation. The most significant species in [[oenology]] is ''[[Saccharomyces cerevisiae]]'', though other genera also contribute to fermentation under certain conditions.<ref>Jancis Robinson, ''Oxford Companion to Wine'', Oxford University Press, 17 Sept. 2015. ISBN 9780198705383.</ref>

== Background ==

The role of yeast in wine was long unknown; fermentations were thought to occur spontaneously without a living agent. The scientific identification of yeast as the driver of fermentation was established in the 19th century, with ''Saccharomyces cerevisiae'' recognised as the principal fermentative organism in wine production.<ref>~~Fleet (ed~~.), ''Wine Microbiology ~~and Biotechnology~~'', ~~Harwood Academic Publishers~~, ~~1993~~, ISBN ~~978-3718653983~~.</ref> Traditionally, fermentations relied on naturally occurring yeasts present on grape skins and in the cellar environment. Today, both spontaneous and inoculated fermentations are employed, depending on stylistic aims.

The role of yeast in wine was long unknown; fermentations were thought to occur spontaneously without a living agent. The scientific identification of yeast as the driver of fermentation was established in the 19th century, with ''Saccharomyces cerevisiae'' recognised as the principal fermentative organism in wine production.<ref>Kenneth C. Fugelsang, ''Wine Microbiology'', Springer, July 31, 1997. ISBN 9780412066115.</ref> Traditionally, fermentations relied on naturally occurring yeasts present on grape skins and in the cellar environment. Today, both spontaneous and inoculated fermentations are employed, depending on stylistic aims.

== Characteristics ==

Yeasts are single-celled microorganisms that reproduce mainly by budding. In the context of wine, their defining trait is the conversion of sugars into ethanol and carbon dioxide, with numerous secondary metabolites that shape [[aroma]] and [[flavour]].<ref>Jackson, ''Wine Science: Principles and Applications''~~, 5th ed.~~, Academic Press, 2020, ISBN ~~978-0128161180~~.</ref> While ''Saccharomyces cerevisiae'' dominates alcoholic fermentation due to its alcohol tolerance and efficiency, other species such as ''[[Brettanomyces]]'' and non-''Saccharomyces'' yeasts may play secondary roles. These can add complexity but also risk spoilage if uncontrolled.

Yeasts are single-celled microorganisms that reproduce mainly by budding. In the context of wine, their defining trait is the conversion of sugars into ethanol and carbon dioxide, with numerous secondary metabolites that shape [[aroma]] and [[flavour]].<ref>PhD Jackson, Ronald S., ''Wine Science: Principles and Applications'', Academic Press Inc, 14 April 2020. ISBN 9780128161180.</ref> While ''Saccharomyces cerevisiae'' dominates alcoholic fermentation due to its alcohol tolerance and efficiency, other species such as ''[[Brettanomyces]]'' and non-''Saccharomyces'' yeasts may play secondary roles. These can add complexity but also risk spoilage if uncontrolled.

== Use in winemaking ==

Winemakers may choose between spontaneous fermentations, relying on wild yeast populations, and inoculation with cultured strains for predictability and control. Commercial strains of ''Saccharomyces cerevisiae'' are selected for attributes such as fermentation vigour, temperature tolerance, and flavour enhancement.<ref>Boulton, Singleton, Bisson & ~~Kunkee~~, ''Principles and Practices of Winemaking'', Springer, ~~1999,~~ ISBN ~~978-0834217011~~.</ref> Non-''Saccharomyces'' yeasts are sometimes encouraged in early stages of fermentation to contribute aromatic diversity before ''Saccharomyces'' takes over.

Winemakers may choose between spontaneous fermentations, relying on wild yeast populations, and inoculation with cultured strains for predictability and control. Commercial strains of ''Saccharomyces cerevisiae'' are selected for attributes such as fermentation vigour, temperature tolerance, and flavour enhancement.<ref>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.</ref> Non-''Saccharomyces'' yeasts are sometimes encouraged in early stages of fermentation to contribute aromatic diversity before ''Saccharomyces'' takes over.

Modern biotechnology has enabled the tailoring of yeast strains for specific outcomes, including enhanced aroma production, reduced volatile [[acidity]], or adaptation to climate-related shifts in grape composition.<ref>Pretorius, “Tailoring wine yeast for the new millennium: Novel approaches to the ancient art of winemaking”, ''Yeast'', Vol. 16, No. 8, 2000, pp. 675–729.</ref> Yeast health and nutrient availability remain critical factors in avoiding sluggish or stuck fermentations.

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-'''Yeast''' (/jiːst/) are unicellular fungi of great importance in [[winemaking]], responsible for the alcoholic [[fermentation]] that transforms [[grape must]] into [[wine]]. The term derives from Old English ''gist'' and Proto-Germanic roots meaning "foam" or "boil", reflecting the frothing effect of fermentation. The most significant species in [[oenology]] is ''[[Saccharomyces cerevisiae]]'', though other genera also contribute to fermentation under certain conditions.<ref>Robinson (ed.), ''The Oxford Companion to Wine'', Oxford University Press, 2015, ISBN 978-0198705383.</ref>
+'''Yeast''' (/jiːst/) are unicellular fungi of great importance in [[winemaking]], responsible for the alcoholic [[fermentation]] that transforms [[grape must]] into [[wine]]. The term derives from Old English ''gist'' and Proto-Germanic roots meaning "foam" or "boil", reflecting the frothing effect of fermentation. The most significant species in [[oenology]] is ''[[Saccharomyces cerevisiae]]'', though other genera also contribute to fermentation under certain conditions.<ref>Jancis Robinson, ''Oxford Companion to Wine'', Oxford University Press, 17 Sept. 2015. ISBN 9780198705383.</ref>
 == Background ==
-The role of yeast in wine was long unknown; fermentations were thought to occur spontaneously without a living agent. The scientific identification of yeast as the driver of fermentation was established in the 19th century, with ''Saccharomyces cerevisiae'' recognised as the principal fermentative organism in wine production.<ref>Fleet (ed.), ''Wine Microbiology and Biotechnology'', Harwood Academic Publishers, 1993, ISBN 978-3718653983.</ref> Traditionally, fermentations relied on naturally occurring yeasts present on grape skins and in the cellar environment. Today, both spontaneous and inoculated fermentations are employed, depending on stylistic aims.
+The role of yeast in wine was long unknown; fermentations were thought to occur spontaneously without a living agent. The scientific identification of yeast as the driver of fermentation was established in the 19th century, with ''Saccharomyces cerevisiae'' recognised as the principal fermentative organism in wine production.<ref>Kenneth C. Fugelsang, ''Wine Microbiology'', Springer, July 31, 1997. ISBN 9780412066115.</ref> Traditionally, fermentations relied on naturally occurring yeasts present on grape skins and in the cellar environment. Today, both spontaneous and inoculated fermentations are employed, depending on stylistic aims.
 == Characteristics ==
-Yeasts are single-celled microorganisms that reproduce mainly by budding. In the context of wine, their defining trait is the conversion of sugars into ethanol and carbon dioxide, with numerous secondary metabolites that shape [[aroma]] and [[flavour]].<ref>Jackson, ''Wine Science: Principles and Applications'', 5th ed., Academic Press, 2020, ISBN 978-0128161180.</ref> While ''Saccharomyces cerevisiae'' dominates alcoholic fermentation due to its alcohol tolerance and efficiency, other species such as ''[[Brettanomyces]]'' and non-''Saccharomyces'' yeasts may play secondary roles. These can add complexity but also risk spoilage if uncontrolled.
+Yeasts are single-celled microorganisms that reproduce mainly by budding. In the context of wine, their defining trait is the conversion of sugars into ethanol and carbon dioxide, with numerous secondary metabolites that shape [[aroma]] and [[flavour]].<ref>PhD Jackson, Ronald S., ''Wine Science: Principles and Applications'', Academic Press Inc, 14 April 2020. ISBN 9780128161180.</ref> While ''Saccharomyces cerevisiae'' dominates alcoholic fermentation due to its alcohol tolerance and efficiency, other species such as ''[[Brettanomyces]]'' and non-''Saccharomyces'' yeasts may play secondary roles. These can add complexity but also risk spoilage if uncontrolled.
 == Use in winemaking ==
-Winemakers may choose between spontaneous fermentations, relying on wild yeast populations, and inoculation with cultured strains for predictability and control. Commercial strains of ''Saccharomyces cerevisiae'' are selected for attributes such as fermentation vigour, temperature tolerance, and flavour enhancement.<ref>Boulton, Singleton, Bisson & Kunkee, ''Principles and Practices of Winemaking'', Springer, 1999, ISBN 978-0834217011.</ref> Non-''Saccharomyces'' yeasts are sometimes encouraged in early stages of fermentation to contribute aromatic diversity before ''Saccharomyces'' takes over.
+Winemakers may choose between spontaneous fermentations, relying on wild yeast populations, and inoculation with cultured strains for predictability and control. Commercial strains of ''Saccharomyces cerevisiae'' are selected for attributes such as fermentation vigour, temperature tolerance, and flavour enhancement.<ref>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.</ref> Non-''Saccharomyces'' yeasts are sometimes encouraged in early stages of fermentation to contribute aromatic diversity before ''Saccharomyces'' takes over.
 Modern biotechnology has enabled the tailoring of yeast strains for specific outcomes, including enhanced aroma production, reduced volatile [[acidity]], or adaptation to climate-related shifts in grape composition.<ref>Pretorius, “Tailoring wine yeast for the new millennium: Novel approaches to the ancient art of winemaking”, ''Yeast'', Vol. 16, No. 8, 2000, pp. 675–729.</ref> Yeast health and nutrient availability remain critical factors in avoiding sluggish or stuck fermentations.