Experiment No.
5
DETERMINATION OF VOLATILE ACIDITY OF WINE
Submitted by:
VAL JASON G. LAGRADA
BS Chem – 4
Submitted to:
PROF. EMMA O. BUNCALES
Chem 82a Instructor
SEPTEMBER 20, 2013
INTRODUCTION
Nowadays, wine industry is growing geometrically due to the increasing demand
throughout the globe. Wine is made by allowing the grapes or other fruits to ferment using yeast
as the catalyst. Yeast speeds up the conversion of sugars, from fruits, to ethyl alcohol.
In order to fully understand how wine is made and the participation of yeast in wine
making, an experiment was performed. Pineapple was used as the primary ingredients of wine.
Pineapple wine is made from the juice of pineapples. Fermentation of the pineapple juice takes
place in temperature-controlled vats and is stopped at near-dryness. The result is a soft, dry, fruit
wine with a strong pineapple bouquet. It is commonly made in Hawaii and Nigeria, the first
pineapple winery in Africa.
In the production of wine, quality control methods are employed to ensure the quality of
the product. These include pH value, Individual wine acids, Total acidity, and Volatile acidity.
One of the most important monitored is the volatile acidity of wine. The volatile acidity is
a test of the state of health of a wine. This is because it is represented principally by acetic acid
that may be formed by the oxidation of ethanol by Mycoderma acetil, the degradation of tartaric
acid by Lactobacillus plantarum or by the degradation of citric acid by Leuconostoc oenos.
Acetic acid then combines with ethanol to form ethyl ethanoate (ethyl acetate), which contributes
to the pungency perceived wines with high volatile acidity. Although limits are imposed for the
amount of this acid in a wine (20 meq/dm) it is a significant increase in the concentration of
acetic acid during the course of vinification or aging that signals a problem with the wine.
The determination of volatile acidity of wine was employed on the pineapple wine to
closely monitor the condition of the wine. The value obtained were compared with the
commercial wine to see the difference between the two.
THEORETICAL BACKGROUND
The acids in wine are an important component in both winemaking and the finished
product of wine. They are present in both grapes and wine, having direct influences on the color,
balance and taste of the wine as well as the growth and vitality of yeast during fermentation and
protecting the wine from bacteria. The measure of the amount of acidity in wine is known as the
titratable acidity or total acidity, which refers to the test that yields the total of all acids present,
while strength of acidity is measured according to pH, with most wines having a pH between 2.9
and 3.9. Generally, the lower the pH, the higher the acidity in the wine. However, there is no
direct connection between total acidity and pH (Bellman & Gallander, 1979).
In wine tasting, the term acidity refers to the fresh, tart and sour attributes of the wine
which are evaluated in relation to how well the acidity balances out the sweetness and bitter
components of the wine such as tannins. Three primary acids are found in wine grapes: tartaric,
malic and citric acids. During the course of winemaking and in the finished wines, acetic,
butyric, lactic and succinic acids can play significant roles. Most of the acids involved with wine
are fixed acids with the notable exception of acetic acid, mostly found in vinegar, which is
volatile and can contribute to the wine fault known as volatile acidity.
Sometimes, additional acids, such as ascorbic, sorbic and sulfurous acids, are used in
winemaking. Wine is one of the most acidic alcoholic beverages with pH values ranging from
2.8 to 3.8 ; white and rosé wines are, in general, more acidic than red wines due to the natural
desacidification as result of the malolactic fermentation (MLF). It is also possible to adjust the
pH of a wine, a procedure that may be required for technological reasons or to protect against
bacterial growth. Tartaric acid (the most abundant acid in grapes and wines) is normally used for
acidification, whereas desacidification – a more unusual and delicate procedure – involves the
addition of either potassium nitrate, or calcium carbonate or potassium hydrogen carbonate.
The acidity of a wine encompasses a number of parameters
1. pH value,
2. Individual wine acids,
3. Total acidity, and
4. Volatile acidity.
The total of a wine is defined as the fraction of non-ionized acids in the wine; officially, it
is determined by the volume of sodium hydroxide required to bring the pH of a specified volume
of wine to 7.00. Individual wine acids. Acids are very important components of wine that in
larger degree determine its quality. Basic acids that exist in wine are tartaric acids and its salts,
and malic acid and its salts. Among these acids, in the wine can be found also acetic, succinic,
citric, lactic acid and their salts.
Carbon dioxide is first removed from the wine. Volatile acids are separated from the wine
by steam distillation and titrated using standard sodium hydroxide. The acidity of free and
combined sulfur dioxide distilled under these conditions should be subtracted from the acidity
of the distillate. The acidity of any sorbic acid, which may have been added to the wine, must
also be subtracted.
Volatile Acidity (VA) in wines is a regulated component, a microbiological monitor, and
a sensory quality indicator. The volatile acidity is a test of the state of health of a wine. Although
many acids in wine are volatile to varying degrees, the volatile acids of interest in this analysis
are more specific than the terminology suggests, and should more accurately be described as the
volatile short chain fatty acids.. This is because it is represented principally by acetic acid.
METHODOLOGY
A. Materials And Reagents
The apparatus and materials needed for the experiment are as follows: distilling flask,
thermometer with rubber stopper, condenser, adapter, graduated cylinder, pipet, aspirator, iron
clamp, iron ring, iron stand, wire gauze, alcohol lamp and beaker.
On the other hand, the reagents needed are as follows: standard 0.1 N NaOH, wine
sample and distilled water.
B. EXPERIMENTATION
I. Preparation of sample
Approximately 50 ml of wine sample was placed in a beaker and was continuously
swirled for 5 minutes to remove dissolved carbon dioxide.
II. Distillation
The CO2 free sample was placed in a distillation flask followed by the addition of 150 ml
recently boiled distilled water. Then, the distillation set-up was assembled. The sample was
distilled until 80 ml of distillate was collected.
III. Determination of Acid Content
The distillate obtained was divided into 3 equal parts, which in case in the experiment 15
ml per parts. Each sample was titrated with standard 0.1 N NaOH using phenolphthalein as
indicator. The endpoint observed was the occurrence of pale pink and the volume of the titrant
was noted. The mass of acetic acid in the aliquot was calculated as was reported as % w/v of
acetic acid per 100 ml sample.
RESULTS AND DISCUSSION
The determination of the % w/v acetic acid was carried out using the conventional
titrimetric method. Appropriate amount of wine was distilled and the collected distillate was
titrated against standard 0.1200 N NaOH. The results were summarized and shown below.
Table 1a. showing the data obtained in the determination of % w/v acetic acid
DESCRIPTIO VOLUME OF VOLUME OF NaOH % w/v ACETIC
N DISTILLATE USED ACID PER 100 G
Trial 1 15.00 ml 0.30 ml 0.0144 %
Trial 2 15.00 ml 0.40 ml 0.0192 %
Trial 3 15.00 ml 0.30 ml 0.0144 %
Mean -- -- 0.016 %
Table 1a showed that the 3 trials were performed with 15.00 ml of wine sample in all the
the trials performed. Trials 1 and 3 has the same volume of NaOH used which is equivalent to
3.6 x 10-5 mol of NaOH. Since based on the equation shown below, 1 mol of NaOH is needed to
neutralized 1 mol of acetic acid, so it means that there is also 3.6 x 10 -5 mol of acetic acid present
in the 15.00 ml wine sample.
NaOH +CH 3 COOH → CH 3 COONa+ H 2 O
In other words, the weight of acetic present in the sample can be easily determined by
multiplying the molar mass of acetic acid by the number of moles of sodium hydroxide. The
solution is shown below for clarity.
w ( acetic acid )=( mol NaOH ) ( 1 mol acetic acid 60 g acetic acid
1mol NaOH )( 1 mol acetic acid )
The weight of the acetic acid that will be obtained using the formula above came from the
15.00 ml aliquot sample. Since, the % w/v acetic acid per 100 ml wine sample is asked (formula
shown below), it will be mutiplied with 100 ml. Then the mean % w/v acetic acid per 100 ml
wine sample was obtained. This value was compared with the commercial wine, Fighter.
w w acetic acid
%
v
acetic acid per 100 ml sample= ( 15.00 ml )
(100 ml )
SUMMARY AND CONCLUSIONS
The determination of the % w/v acetic acid was carried out using the conventional
titrimetric method. Appropriate amount of wine was distilled and the collected distillate was
titrated against standard 0.1200 N NaOH until the occurrence of pale pink color which indicates
end point of the reaction. From the volume of NaOH used, the % w/v of acetic acid used was
easily determined. The mean value of % w/v of acetic acid per 100 ml sample is 0.016 % which
is still within the recommended value for wines.
Based on the above findings, the following conclusions were made:
1. That the wine produced has low acetic acid which indicates it’s safe for
consumption; and
2. That the wine made is safer to use than the commercial wine due to its low acetic
acid value compared to the commercial wine.
REFERENCES
Bellassai, S. 2013. Determination of the Acetic acid (volatile acidity) in wine. Available at
http://www.cdrfoodlab.com/food-analysis/volatile-acidity-wine.html, Retrieved
on 23 September 2013.
Bellman, R. B. and Gallander, J. F. (1979). Wine Deacidification. In Chichester, C. O.; Mrak,
Emil Marcel; Stewart, George Franklin. Advances in Food Research Vol. 25.
Academic Press. p. 3. ISBN 0-12-016425-6. Retrieved 2013-09-20.
Robinson, J. 2006. The Oxford Companion to Wine” Third Editio. Oxford University Press.
