葡萄酒酿造科学英文资料：L6, Whites, juice to bottled wine
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http://upload.wikimedia.org/wikipedia/commons/e/ea/Contre_la_chaptalisation.jpg
Acidification and deacBiblioteka Baidudification
Add L (+) tartaric acid
Malic acid in berries decline by respiration
• juice oxidation and aerobic yeast propagation usually adequate • oxygen is incorporated during cap management of red wine
fermentations • problem situations include highly clarified juices and high sugar
Factors affecting fermentations
Aeration
Fermentation requires no oxygen but can be assisted by allowing biosynthesis of sterols and long-chain fatty acids
• fruity esters such as isoamyl, isobutyl and hexyl acetates are synthesised and retained to a greater degree at cool temperatures
• maximum concentrations of fatty acid ethyl esters (such as ethyl octanoate and ethyl decanoate) are obtained at higher temperature
• sur lies: during autolysis, macromolecular components (especially mannoproteins) are released
• increase in fullness/body, phenolic concentration reduced, tartrate and protein stability increased
Products
http://en.wikipedia.org/wiki/Yeast
Ethanol Unfermented
By-products Yeast cells Carbon dioxide
http://enology.umn.edu/wp-content/uploads/yeast-growth.png
MLF converts malic acid to lactic acid
Direct addition of KHCO3 or CaCO3 neutralises H+
The double salt method removes tartrate and malate in proportion
Whites
Juice to bottled wine
Lecture 6
Chaptalisation
The process of adding sugar to must to increase alcohol
• regulations vary • add sucrose when yeast
multiplication is more or less complete • also increases other fermentation by-products
• greatest concentrations of higher alcohols are found in wines fermented at temperatures in the range 25-30C
Racking, yeast lees and oak barrels
White juice may be fermented and remain in the same barrel with yeast lees
Fermentation
The conversion of glucose and fructose to ethanol by yeasts:
Saccharomyces cerevisiae Saccharomyses bayanus
Strains differ in their tolerance for conditions and in their by-products
content musts
Factors affecting fermentations
Temperature
Fermentation can occur in the range 5 to 38C but temperature has an important effect on volatile compounds
Factors affecting fermentations
Yeast assimilable nitrogen (YAN)
YAN = NH4+ plus amino acids except proline
• low YAN musts tend to produce H2S which can result in unpleasant and difficult to remove organic-S compounds
• battonage: prevents excessive reducing conditions and oxidises H2S
• aim for initial YAN > 250 mg/L
• late stage H2S is particularly problematic
• thiols can be removed by Cu fining but difficult and may affect varietal character
Acidification and deacBiblioteka Baidudification
Add L (+) tartaric acid
Malic acid in berries decline by respiration
• juice oxidation and aerobic yeast propagation usually adequate • oxygen is incorporated during cap management of red wine
fermentations • problem situations include highly clarified juices and high sugar
Factors affecting fermentations
Aeration
Fermentation requires no oxygen but can be assisted by allowing biosynthesis of sterols and long-chain fatty acids
• fruity esters such as isoamyl, isobutyl and hexyl acetates are synthesised and retained to a greater degree at cool temperatures
• maximum concentrations of fatty acid ethyl esters (such as ethyl octanoate and ethyl decanoate) are obtained at higher temperature
• sur lies: during autolysis, macromolecular components (especially mannoproteins) are released
• increase in fullness/body, phenolic concentration reduced, tartrate and protein stability increased
Products
http://en.wikipedia.org/wiki/Yeast
Ethanol Unfermented
By-products Yeast cells Carbon dioxide
http://enology.umn.edu/wp-content/uploads/yeast-growth.png
MLF converts malic acid to lactic acid
Direct addition of KHCO3 or CaCO3 neutralises H+
The double salt method removes tartrate and malate in proportion
Whites
Juice to bottled wine
Lecture 6
Chaptalisation
The process of adding sugar to must to increase alcohol
• regulations vary • add sucrose when yeast
multiplication is more or less complete • also increases other fermentation by-products
• greatest concentrations of higher alcohols are found in wines fermented at temperatures in the range 25-30C
Racking, yeast lees and oak barrels
White juice may be fermented and remain in the same barrel with yeast lees
Fermentation
The conversion of glucose and fructose to ethanol by yeasts:
Saccharomyces cerevisiae Saccharomyses bayanus
Strains differ in their tolerance for conditions and in their by-products
content musts
Factors affecting fermentations
Temperature
Fermentation can occur in the range 5 to 38C but temperature has an important effect on volatile compounds
Factors affecting fermentations
Yeast assimilable nitrogen (YAN)
YAN = NH4+ plus amino acids except proline
• low YAN musts tend to produce H2S which can result in unpleasant and difficult to remove organic-S compounds
• battonage: prevents excessive reducing conditions and oxidises H2S
• aim for initial YAN > 250 mg/L
• late stage H2S is particularly problematic
• thiols can be removed by Cu fining but difficult and may affect varietal character