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Acids

Why do soft drinks contain acid?

Some ingredients are present in virtually every soft drink. Acid is one of these basic ingredients and acidity forms one of the basic properties of a soft drink.

Acid is used in soft drink products to fulfil two main functions. Firstly, acidity is a key factor in the taste profile of a drink as it balances the sweetness. People generally prefer more acidic foods and drinks. Secondly, it inhibits the growth of micro-organisms such as yeasts, moulds and bacteria.


How do acids prevent the growth of pathogenic organisms in soft drinks?

Most bacteria grow in moist, warm environments that avoid extremes of acidity or alkalinity. The main food poisoning organisms also require near neutral conditions to grow and multiply. Therefore an acidic environment ensures the safety of a product by providing conditions which do not allow pathogenic organisms survive. High acid foods with a pH less than 4.5 are generally regarded as safe from pathogens.


Which acids are used in soft drinks?

Soft drinks are acidified either by the addition of fruit juice or by the inclusion of an acid. The three most commonly used acids are citric acid, malic acid and phosphoric acid. Citric acid is found naturally in citrus fruits, blackcurrants, strawberries and raspberries. Malic acid is found in apples, cherries, plums and peaches. Phosphoric acid is generally used in cola drinks. It is a stronger acid and so imparts a different taste profile.


How much acid is used in a soft drink?

The amount of acid used in soft drinks depends on the individual product recipe and the type of acid used; the stronger the acid the less is required to make the final drink. For example very little phosphoric acid needs to be added to a cola drink as it is a very strong acid.

A: Carbonates

% acid
pH level

Ready to drink [1,2]

0.2 - 0.5%

2.6 - 3.0

Lemon flavoured soft drinks [2]

up to 0.7%

2.6 - 2.9

Low-calorie drinks [3]

0.2 - 0.7%

3.0 - 3.2

Cola drinks [4]

0.06%

2.4 - 2.8

Low calorie cola drinks [4]

0.06%

2.6 - 3.0

B: Fruit Juices
% acid
pH level

Orange

0.75 - 1%

3.4 - 3.6

Apple [5]

0.4 - 0.7%

3.4 - 3.8

Grapefruit

1.1 - 1.6%

3.2 - 3.4

Pineapple

0.4 - 1%

3.3 - 3.7

Lemon

4.6 - 6.4%

3.0 - 3.2

Tomato [6]

0.3 - 0.45%

4.0 - 4.5

Sweetened Grapefruit

1.1 - 1.6%

3.1 - 3.4

C: Bottled Waters
% acid
pH level

Natural Mineral Water - still

0

6.8 - 7.8

Natural Mineral Water - carbonated

slight acidity as an effect of carbonation

4.2 - 4.8

Spring Water - still

0

6.8 - 7.8

Spring Water - carbonated

slight acidity as an effect of carbonation
4.2 - 4.8

Table Water - still

0

6.8 - 7.8

Table Water - carbonated

slight acidity as an effect of carbonation
4.2 - 4.8
D: Still and dilutable drinks
% acid
pH level

Dilutable soft drinks [2]

0.15 - 0.25%

2.6 - 3.0

Lemon flavoured dilutables [2]

up to 0.4%

2.6 - 3.0

Low calorie dilutables [2]

0.15 - 0.4%

3.0 - 3.2

[1] Excludes cola and lemon flavoured drinks
[2] Contains citric acid
[3] Excludes cola drinks
[4] Contains phosphoric acis
[5] Contains malic acid
[6] Tomato juice is usually controlled to a pH level of less than 4.3 by addition of citric acid to prevent the growth of pathogens.


Is there a relationship between the total acidity of a drink and its pH?

No, there is no direct relationship. Acidity represents the total quantity of acidic material present whereas pH is a measure of the strength of the acid present, i.e. the concentration of hydrogen ions.

The relationship between acidity and pH is in fact affected by the presence of acidity regulators or carbon dioxide which are added to the drink to buffer the pH.


Do soft drinks containing acids have an influence on dental health?

Many other food and drink products such as fruit, sauces, pickle and wine contain acid, whether natural or added, in the same way that soft drinks do. However an acid can only have an influence on enamel erosion for as long as that acid is in contact with the enamel surface of teeth. Soft drinks normally have little contact with teeth when compared to other foods. Studies on dental erosion have shown it to be dependent on several different factors. This means that susceptibility in individuals varies according to behaviour, lifestyle, diet and oral hygiene practice.


Links.

Q&As on Phosphoric Acid

click here

Food Additives and Ingredients Association

www.faia.org.uk

     
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