Vietnam National University, Hochiminh city International University

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PHAM VAN HUNG PhD
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PHAM VAN HUNG, PhD
Department of Food Technology
School of Biotechnology, International University
Yeast in wine production
Yeasts occur on the skins of most fruits and if the
fruits are mashed, the sugar-containing juices begin
to ferment.
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Yeast on the outside
of grapes
Yeast in wine production
The role of yeast in winemaking is the most
important element that distinguishes wine from
grape juice.
In the absence of oxygen yeast converts the
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In the absence of oxygen, yeast converts the
sugars of wine grapes into alcohol and carbon
dioxide through the process of fermentation.
The more sugars in the grapes, the higher the
potential alcohol level of the wine if the yeast are
allowed to carry out fermentation to dryness.
Yeast in wine production
For most of the history of wine, winemakers did
not know the mechanism that somehow converted
sugary grape juice into alcoholic wine.
They could observe the fermentation process
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which was often described as "boiling", "seething"
or the wine being "troubled" due to release of
carbon dioxide that gave the wine a frothy,
bubbling appearance.
This history is preserved in the etymology of the
word "yeast" itself which essentially means "to
boil“.

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Yeast in wine production
The wine being “troubled”.
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Yeast in wine production
In the mid‐19th century, the
French scientist Louis Pasteur
uncovered the connection
between microscopic yeast cells
and the process of the
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p
fermentation.
Pasteur discovered that yeast
converted sugars in the must
into alcohol and carbon dioxide.
His work would later lead to
Pasteur being considered one of
the "Fathers of Microbiology”.
Yeast in wine production
The yeast species were commonly known as
Saccharomyces cerevisiae.
Throughout the 20th century, more than 700
different strains of Saccharomyces cerevisiae were
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different strains of Saccharomyces cerevisiae were
identified.
The difference between the vast majority of these
strains are mostly minor, though individual
winemakers will develop a preference for particular
strains when making certain wines or working with
particular grape varieties.
Yeast in wine production
The characteristics of yeast in wine production.
Acid Tolerance
Temperature range
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Sulfite resistance – Vineyard and Winery
Fermentation speed
Alcohol tolerance
Nitrogen requirement
Production of volatile sulfur compounds

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Yeast in wine production
Wild yeasts
wild yeasts are often referred to as ambient, indigenous or
natural yeast.
Another use of the term "wild yeast" refers to the non‐
Saccharomyces genera of yeasts.
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Saccharomyces genera of yeasts.
Native strains may have greater potential for change
(instability).
Inoculated yeasts
Inoculated (or pure cultured) yeasts are strains of
Saccharomyces cerevisiae that have been identified and
plated from wineries across the world.
These strains are tested in laboratories to determine a strain's
characteristics
Yeast in wine production
Saccharomyces species:
Saccharomyces cerevisiae
Saccharomyces bayanus
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Saccharomyces beticus
Saccharomyces fermentati
Saccharomyces paradoxus
Saccharomyces pastorianus
Saccharomyces uvarum
Yeast in wine production
Other genera:
Brettanomyces
Candida
Kloeckera the most common "wild yeast" found in the
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vineyard.
Saccharomycodes
Schizosaccharomyces,
Zygosaccharomyces: can grow in wines up to 18% v/v
and extremely high sugar levels and is very resistant to
sulfur dioxide.
Aureobasidium
Yeast in wine production
Choosing a yeast strain:
Grape varietal
Brix and alcohol
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Fermentation temperature
Additions
Production capacity
Wine making style

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Yeast in wine production
Stuck fermentation:
A stuck fermentation occurs in brewing beer or
winemaking when the yeast become dormant: the yeasts
become exhausted of available nutrients, and the wine
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has not yet reached dryness.
is an unintentional and unwanted occurrence that can
lead to the wine being spoiled by bacteria and oxidation.
to limit the possibility of a stuck fermentation occurring
by adding nitrogen to the must in the form
diammonium phosphate or using cultured yeast with a
high temperature and alcohol tolerance.
Wine production process
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Wine production process
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Wine production process
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White Wine‐Making Red Wine‐Making

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1. Viticulture
Factors which inflence grape’s flavor:
• climate of the vineyard’s region
• drainage around the vines
• humidity of the region
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• sun exposure.
• soil quality
2. Harvesting
• Grappes are picked up by hand or
mechanically
• Descision of harvest informed by level of
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• Descision of harvest informed by level of
sugar and acid
• weather forecasts
3. Stemming/Crushing
Stemming is the separation of the stems and
grapes (which are sends to the press)
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Crushing: A horizontal press squeezes
the broken grapes, separating the
fresh juice (must) from the skins
(marc).
4. Fermentation
• sugar and acids that naturally
react with wild yeasts
• Vineyard adding their own yeasts
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• fermentation can take from 10 to
30 days to convert natural sugar to
alcohol.

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Fermentation
Primary fermentation is conversion of sugar into EtOH
and CO2 is carried out under anaerobic conditions.
Anaerobic: Lacking oxygen
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C6H12O6 −> 2CH3CH2OH + 2CO2
Heat is a by‐product of reaction
Yeast can be killed if temperature gets too high. Above
38°C problems occur.
Fermentation temperature can be regulated
CO2 is dangerous by‐product that needs to be managed
5. Draining
Liquid wine is drained from the vat without being pressed and go into
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barrels (free‐run wine). The remaining pulp retains about 20% of the
wine.
6. Pressing
The remaing pulp, after draining, is pressed to
squeeze out the press wine The press wine tends
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squeeze out the press wine. The press wine tends
to be dark, harsh and unpalatable, and is mixed
with free‐run wine to produce something decent.
7. Mixing
The free‐run wine and press wine, always from the same source, are mixed
together in appropriate ratios to obtain the desired balance.
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8. Clarification
Clarification is the step of stabilization of fermentation. During
clarification all remaining solids are removed from the
fermented liquid.
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Clarification done in numerous ways:
• fining, a process that calls for the addition of substances that
cause the solids in the liquid to adhere to one another and
sink to the bottom of the vat
• running the liquid through coarse and fine filters
• siphoning the liquid off the top of the fermenting vats after
the solids have settled to the bottom
9. Aging
The final stage in vinification is aging the
wine. At this point, the clarified wine is
transferred into either wooden barrels or
metal vats in which the wine is allowed to
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further mature and develop flavors. If a
winemaker chooses to age the wine in
wooden casks, he will be allowing the wine
to pick up flavors from the wood, adding
greater depth to its flavors. While this can
add body to some wines, keep in mind that
the “woody” flavor isn’t suited to all types
of wine, hence the use of metal vats.
10. Bottling
The final step of wine production.
A dose of sulfite is added to help
preserve the wine and prevent
unwanted fermentation in the
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bottle.
The wine bottles then are
traditionally sealed with a cork,
although alternative wine
clossure such as synthetic corks
and screwcaps, which are less
subject to cork taint, are
becoming increasingly popular.
Les Grands Crus
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Equipments
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Crusher
Equipments
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Small Bladder Press
Equipments
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Large Rotary Press
Add yeast to must in fermentation vessel,
cover for 3 days to several weeks
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Fermentation Tanks

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Siphon wine off the sediments (lees) into
clean secondary fermentation vessel
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Barrel filling
Aging
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Barrel aging
Bottle when wine is clear and all fermentation
has stopped
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Bottling line
Bottles being filled
Bottle storage
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Large Commercial Cellar Small in-home cellar

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Wine quality control
The sugar in wine is mainly glucose and fructose, with
traces of arabinose, xylose and other sugars that are
not fermentable by yeast,but can be attacked by
bacteria
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bacteria.
Residual sugar is the sugar left after fermentation has
finished or been stopped, measured in grams per litre.
A dry wine has virtually none.
Wine quality control
Alcohol content (mainly ethyl alcohol) is expressed in percent by
volume of the total liquid. (Also known as “degrees”). Table wines
are usually between 11.5° and 13.5°, though up to 15° is increasingly
seen.
Acidity is both fixed and volatile.
i d idi i i i ll f i li d i i
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Fixed acidity consists principally of tartaric, malic and citric
acids, all found in the grape, and lactic and succinic
acids,produced during fermentation.
Volatile acidity consists mainly of acetic acid, which is rapidly
formed by bacteria in the presence of oxygen.
pH is a measure of the strength of the acidity. Wine usually ranges
from pH 2.8 to 3.8. High pH can be a problem in hot climates.
Lower pH gives better colour, helps stop bacterial spoilage and
allows more of the SO2 to be free and active as a preservative.
Wine quality control
Sulphur dioxide (SO2) is added to prevent oxidation and other
accidents in winemaking. Some of it combines with sugars etc
and is “bound”. Onlythe “free” SO2 is effective as a preservative.
Total SO2 is controlled by law according to the level of residual
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sugar: the more sugar, the moreSO2 is needed.
Tannins are the focus of attention for red winemakers intent on
producing softer, more approachable wines.
Toast refers to the burning of the inside of the barrel. “High
toast” givesthe wine caramel‐like flavours.
Wine Analysis
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Sugar Measurement
Sugar (glucose and fructose) is the most abundant
compound(s) found in berry.
Other berry constituents are synthesized from it.
Abundance allows indirect methodology for measurement
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Abundance allows indirect methodology for measurement.
(Unit Brix=% or g/100 mL)
Hydrometer used in winery to monitor fermentation. (Based
on Archimedes principal)
Refractometer used in vineyard. (Uses refractive index of
sugars)
Determination of alcohol content
Record starting specific gravity of must (S1),
Record finished specific gravity (S2)
Calculate by using the formula
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36.7
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(%)
SS
Alcohol
−
=
Organic Acid Measurement
Measured by titrating with a base of known
concentration in the presence of a chemical indicator
with a known pH end point.
Thi ll d i bl idi (TA)
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This measurement called titratable acidity (TA)
pH is measured either with a meter or litmus paper.
Concentrations range from 8.0 g/L to 6.5 g/L
pH ranges from 2.8 to 4.0.
White wine 3.0‐3.3 Red wine 3.2‐3.4
Other Parameters?
Anthocyanin and tannin content in red grapes
Total phenols in white grapes.
Grape and wine relationship not well established for
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Grape and wine relationship not well established for
either because of processing effects.
Aroma compounds in grape difficult to measure.

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Wine making problem
The major cause of wine failures is a lack of proper
sterilization procedures and practices. Important Problems
encountered are:
1. Corkiness
Symptoms: An unpleasant flavor in wine
P ibl C
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Possible Causes:
a. Bottling with a defective cork
b. Not a complete seal and the outside air allowed to enter into the
bottle
c. Inferior cork
2. Soapiness
Symptoms: Soapy taste in your favorite wine
Possible Causes:
a. Equipment, carboys and Fermenters not properly cleaned and rinsed.
Wine making problem
3. Woody
Symptoms: Aroma of wood in your wine.
Possible Causes:
a. Over‐soaking of corks
b O i ith k hi
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b. Over‐aging with oak chips
4. Flowers of Wine
Symptoms: A white film or skin that forms on the surface of wines
Possible Causes:
a. Undue exposure to air
Wine making problem
5. Stuck Fermentation
Symptoms: Wine has stopped fermenting before reaching a specific
gravity of 0.994 ‐ 0.996
Possible Causes:
a cold temperatures / too hot
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a. cold temperatures / too hot
b. Bad yeast, using a yeast that's reached its limit of alcohol tolerance
c. Too much sugar
d. Insufficient nutrients or acids
e. Insufficient oxygen
f. Too much carbon dioxide
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The end!