Acid value testing is an important chemical analysis used to assess the quality and condition of fats and oils. The test measures the amount of alkaline solution required to neutralise acidic compounds present in a sample and is commonly used as an indicator of the amount of free fatty acids (FFAs) present.
For manufacturers, food producers, suppliers and quality-control teams, acid value analysis can provide useful information about raw materials, processing, storage and finished-product quality.
What Is Acid Value?
The acid value of an oil or fat is defined as the amount of potassium hydroxide (KOH), expressed in milligrams, required to neutralise the acidic constituents in one gram of sample.
Acid value is generally reported as:
mg KOH/g sample
A higher acid value generally indicates a greater quantity of acidic material requiring neutralisation.
However, acid value should not automatically be interpreted as a direct measurement of product deterioration. Results need to be considered in relation to the sample type, applicable specification, analytical method and product history.
The current ISO 660:2020 standard specifies methods for determining acidity in animal and vegetable fats and oils, with acidity preferably expressed as acid value. The standard includes two titrimetric methods and one potentiometric method.
What Are Free Fatty Acids?
Fats and oils are primarily made up of triglycerides. Under certain conditions, triglycerides can undergo hydrolysis, resulting in the release of free fatty acids.
This can be influenced by factors such as:
- Moisture
- Heat
- Enzymatic activity
- Processing conditions
- Storage conditions
- Length of storage
- Raw material quality
Free fatty acids can therefore be an important consideration when evaluating the chemical quality of fats and oils.
It is important to remember, however, that free fatty acids can occur naturally and that the presence of FFAs does not by itself establish that an oil is unsafe or unsuitable.
What Is Acid Value Titration?
Acid value titration is an analytical technique based on an acid-base neutralisation reaction.
During a typical acid value determination, a measured quantity of fat or oil is prepared using an appropriate solvent. A standardised alkaline solution, commonly potassium hydroxide, is then used to titrate the acidic components in the sample.
An indicator or suitable instrumental endpoint is used to determine when the neutralisation reaction has reached the required endpoint.
The quantity of alkali consumed is then used to calculate the acid value.
In simple terms:
Sample + standardised KOH → neutralisation of acidic components → acid value calculation
The precise procedure depends on the analytical method being used and the characteristics of the sample.
How Is Acid Value Calculated?
The acid value is calculated from the amount and concentration of alkali used during the titration, together with the sample mass and other method-specific parameters.
A simplified representation of the calculation is:
Acid Value (mg KOH/g) = amount of KOH required for neutralisation ÷ sample mass
In laboratory analysis, the exact calculation must account for the concentration of the standardised titrant and the relevant blank correction and analytical conditions specified by the method.
For this reason, acid value calculation should be performed according to the applicable validated or standardised analytical method rather than relying on a generic formula.
What Does a High Acid Value Mean?
A high acid value means that a greater quantity of alkaline solution was required to neutralise acidic components in the tested sample.
In fats and oils, this can be associated with an increased concentration of free fatty acids.
Potential factors include:
- Hydrolysis of triglycerides
- Exposure to moisture
- Enzymatic activity
- Processing conditions
- Storage conditions
- Extended storage
- Raw material characteristics
However, a high acid value does not have one universal interpretation.
For example, acceptable acid-value limits can differ significantly between different types of oils, fats and products. Results should therefore be compared with the relevant product specification, standard or customer requirement.
Why Is Acid Value Testing Important?
1. Raw Material Quality Control
Manufacturers can use acid value testing when assessing incoming oils and fats.
Testing can help establish whether a raw material meets the required chemical specification before it enters production.
2. Finished Product Testing
Where appropriate, acid value can form part of a broader food chemistry testing programme for finished products.
Results can be compared with product specifications and previous batches to monitor consistency.
3. Monitoring Storage Conditions
Fats and oils can undergo chemical changes during storage.
Routine oil quality testing can help identify changes over time and support investigations where an unexpected increase in acid value is observed.
4. Investigating Product Quality
When a product shows changes in quality, taste, odour, appearance or other characteristics, chemical testing can help provide additional information for an investigation.
Acid value may be considered alongside other analytical parameters depending on the product and investigation.
Acid Value vs Free Fatty Acid Content
Acid value and free fatty acid content are related, but they are not exactly the same measurement.
Acid value measures the amount of alkali required to neutralise acidic components and is reported in mg KOH/g.
Free fatty acid content is generally expressed as a percentage, often calculated using a specified fatty acid as the basis.
The relationship between acid value and FFA content depends on the fatty acid used for the calculation.
Therefore, laboratories should report the result according to the applicable analytical method and reporting requirements rather than treating acid value and FFA percentage as automatically interchangeable.
Acid Value vs Peroxide Value
Acid value is also different from peroxide value.
| Test | What it measures | Typical purpose |
|---|---|---|
| Acid value | Acidic components/free fatty acids | Assess acidity and monitor changes in fats and oils |
| Peroxide value | Primary oxidation products | Assess primary lipid oxidation |
| Free fatty acids | Free fatty acid content | Characterise acidity in fats and oils |
Using more than one analytical parameter can provide a more comprehensive understanding of the condition of a fat or oil.
The appropriate tests depend on the product, specification and reason for testing.
What Types of Samples Can Be Tested?
Acid value determination may be applicable to a range of fats and oils, including:
- Vegetable oils
- Animal fats
- Edible oils
- Crude oils
- Refined oils
- Oil-containing food products
- Fat-containing raw materials
- Selected cosmetic ingredients
- Technical fatty acids
ISO 660:2020 specifically covers refined and crude vegetable or animal fats and oils, soap stock fatty acids and technical fatty acids, while excluding waxes and milk and milk products from its scope.
Acid Value Testing and International Standards
The choice of analytical method is important when performing acid value testing.
ISO 660:2020 – Animal and vegetable fats and oils — Determination of acid value and acidity is an international standard specifically addressing the determination of acidity in animal and vegetable fats and oils. It remains the current ISO edition.
Codex Alimentarius also maintains standards relating to fats and oils, including:
- CXS 19-1981 – Standard for Edible Fats and Oils Not Covered by Individual Standards
- CXS 210-1999 – Standard for Named Vegetable Oils
- CXS 211-1999 – Standard for Named Animal Fats
These standards form part of the international Codex framework for fats and oils.
The applicable standard and acceptance criteria will depend on the specific product being tested.
Why Use a Laboratory for Acid Value Analysis?
Accurate acid value determination depends on appropriate sample preparation, standardised reagents, controlled titration conditions and suitable quality-control procedures.
A laboratory can provide a documented analytical result that can be compared against:
- Product specifications
- Customer requirements
- Applicable standards
- Previous batch results
- Internal quality-control limits
This makes acid value laboratory testing useful for both routine quality control and product investigations.
Acid Value Testing at Envirocare Laboratory
Envirocare Laboratory provides chemistry testing to support businesses with analytical requirements across a range of products and industries.
If you need acid value testing, oil quality testing, free fatty acid analysis or other chemistry testing, our laboratory team can assist with determining the appropriate analytical requirements for your sample.
Whether you are checking a raw material, comparing production batches or investigating a product-quality concern, laboratory analysis can provide objective chemical data to support your quality-control process.
Test for What Matters.
📞 +27 18 294 4283
📧 info@envirocarelab.co.za
References
- International Organization for Standardization (ISO). (2020). ISO 660:2020: Animal and vegetable fats and oils — Determination of acid value and acidity. Geneva: ISO.
- Codex Alimentarius Commission. (2024). CXS 19-1981: Standard for Edible Fats and Oils Not Covered by Individual Standards. FAO/WHO.
- Codex Alimentarius Commission. (2025). CXS 210-1999: Standard for Named Vegetable Oils. FAO/WHO.
- Codex Alimentarius Commission. (2024). CXS 211-1999: Standard for Named Animal Fats. FAO/WHO.
