This experiment aims to produce white wine through yeast fermentation of grape juice. The key materials needed are yeast culture, grape juice, sucrose, and various chemicals. White wine is produced when yeast cells in grape juice biochemically convert sugars like glucose and fructose into ethanol and other compounds, imparting characteristics of taste, aroma, and alcohol content. The process involves inoculating crushed grape must with wine-producing yeast, followed by aerobic and then anaerobic incubation over 3-5 weeks. Properties of the fermenting wine are examined weekly to track changes in taste, odor, clarity, acidity, volatile acidity, and alcohol content.

1. Dr. Imran Sajid

2. Experiment: Production of white wine by
the fermentative activity of yeast
Materials Required
• Yeast culture (Saccharomyces cerevisiae)
• Grapes juice
• Sucrose
• Potassium metabisulphite
• 0.1 N NaOH
• 1% phenolphthalein (used as indicator)
• 100 ml, 500 ml flasks
• Measuring cylinder
• Biurets
• Test tubes etc.

3. Principle (Theoretical Background)
White wine is the product of the fermentation of fruit juices, like
grapes, strawberries, peaches, plums, apples etc. The yeast cell
biochemically convert the sugars of grape juice like glucose and
fructose into acetaldehyde and then in to ethanol. Grapes having
20-30% sugars will yield wine with alcohol content of 10-15%
ethanol. Acids and minerals present in the juice gives
characteristics taste to wine and their concentration increases in
the finished product. For red wines crushed grapes must be
fermented with their skin which gives color to the wine.
However white wine is produced only from juices of the grapes.
The commercial production of white wine is a long process. First
of all the grapes are crushed or pressed to get their juice called
“Must”. Potassium metabisulphite is added to the must which
retards growth of the bacteria, mold and wild yeast which are
endogenous to grapes wine yards.

4. Glucose Acetic acid acetaldehyde
Ethanol

5. Then the must inoculated with wine producing yeast. The
inoculated must is incubated under aerobic conditions for 3 to 5
days at 20-25C. This is followed by the anaerobic incubation for
about 20 days. Later the wine is aged for about 1-5 years in aging
tanks or wooden barrels. During aging wine is clearified of any
turbidity of any turbidity producing volatile esters that gives
characteristics flavor to wine. The clarified product is pasteurized
and is bottled. This experiment is modified method in which
white wine is produced from grapes juice.
The fermenting wine is examined at one week interval for the
following characteristics

6. 1. Taste: Bitter, soure, sweet or salty
2. Odor/Aroma: Fruity, sweety or yeast like
3. Clarity: clear or turbid
4. Total acidity: measured as % of tartaric acid
5. Volatile acidity: measured as % of acetic acid
6. Alcoholic content: measured as % of ethanol (measured with
ebuliometer).
Titration Procedure
• Take 1 ml of fermenting wine in a conical flask and add 10 ml
of distilled water in it.
• Add few drops of 1% phenolphthalein as indicator
• Mix and titrate against 0.1 N NaOH up to the first persistant
pink color
• Record the quantity of alkali used (get average of three
readings)

8. Procedure
1. Pour 500 ml grape juice in to a 1 liter flask and standardize
the grape juice
2. Add 20 g of sucrose in to the juice
3. Inoculate the juice with 50 ml of yeast culture (already grown
in the grape juice)
4. Close the flask with a stopper of cotton plug which allow
aeration and incubate under aerobic conditions
5. After 2 days and 4 days on incubation add 20 g of sucrose
each time in to the fermenting juice
6. After 5 days incubate the fermenting wine under anaerobic
conditions for 21 days
7. Records your observations and results in the form of atable

9. S.
No.
Tests Grape Juice Fermenting wine
7 Days 15 Days 21 days
1.
2.
3.
4.
5.
6.
Taste
Odor/Aroma
Turbidity
Total acidity
Volatile acidity
Alcohol content
Observations and Results