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Note: This article was AI-translated from Arabic and is currently under manual review. The author is not responsible for any translation errors. Please refer to the original Arabic text for the most accurate and authoritative information.
Cloud point and iodine value: the relationship that reveals the secrets of molecular composition, crystallization kinetics and cold stability... with a reference table and practical applications for the oils and fats industry.
Two shipments of palm olein carry the same iodine value, match on a number of conventional quality indicators, and are stored under the same conditions; yet with the first cold spell, one stays clear and golden while the other turns cloudy and white crystals appear in it!
So is the cloudy oil of lower quality? Does the appearance of crystals mean it is adulterated or spoiled? And how can two oils behave differently despite having the same iodine value (Iodine Value – IV)?
And the most important question for specialists, manufacturers and importers:
Can the cloud point of palm olein (Cloud Point – CP) be predicted from the iodine value alone?
These are not merely academic questions; they are industrial and commercial issues that affect product quality, the efficiency of fractionation operations, production cost, consumer acceptance, and how well the oil suits storage and handling conditions.
Scientific studies reveal a clear inverse relationship, as a general trend, between iodine value and cloud point: the higher the degree of unsaturation, the lower the temperature at which cloudiness usually appears, and the better the oil's ability to remain liquid and clear at low temperatures.
But the scientific surprise is that this relationship is not a fixed mathematical equation that applies to all grades of palm olein.
Behind it lies a world of molecular detail that begins with the nature of triglycerides and diglycerides, passes through crystal formation and growth, and ends with the effect of the fractionation method, the thermal history of the oil, and the length of time it is exposed to cold.
Hence the fundamental truth:
Cloud point is not just a number on a certificate of analysis; it is a fingerprint that reveals the oil's molecular composition and its behaviour under the effect of cold.
The cloud point (Cloud Point – CP) is the temperature at which the cloudiness caused by the early stages of crystallization of certain fat components becomes observable or detectable as the oil is cooled, according to a specified test method.
When the temperature of palm olein (Palm Olein) drops, the solubility of some higher-melting glycerides decreases, and the medium becomes ready for the formation of fine crystal nuclei, which gradually grow until they are able to scatter light and cause cloudiness.
However, three terms must be distinguished:
Cloud point (Cloud Point): the temperature at which cloudiness appears or is detected under the measurement conditions.
Crystallization onset (Crystallization Onset): the beginning of the formation of the crystalline phase, which can be determined by suitable analytical techniques, including differential scanning calorimetry.
Cold stability (Cold Stability): the ability of the oil to retain its clarity for a specified period of time at a low temperature.
Although the three indicators are related, they do not measure the same property.
The result is affected by the test method, the cooling rate, sample preparation and the sample's thermal history.
Well-known methods include:
It must not be assumed that the crystallization onset temperature measured by DSC automatically matches the cloud point measured visually or by the Mettler method.
The basic scientific rule is that a valid comparison of results between laboratories requires standardizing the measurement method, sample preparation, cooling conditions and the analytical end point.
The iodine value (Iodine Value – IV) is a chemical indicator of the total degree of unsaturation in oils and fats, expressed as grams of iodine that react with 100 grams of oil.
Palm olein contains a mixture of fatty acids, the most important of which are:
In general, a higher proportion of unsaturated fatty acids raises the iodine value, while a lower proportion of high-melting glycerides helps improve the oil's fluidity and its relative stability in the cold.
Hence the well-known inverse relationship:
Higher iodine value IV → usually a lower cloud point CP → improved relative cold stability.
But this relationship does not mean that each iodine value has a single, fixed cloud point.
The iodine value does not determine how fatty acids are distributed within the triglycerides, nor does it reveal the proportions of the different glycerides or the positional isomers.
The study by Danthine and colleagues, published in 2017 in the Journal of the American Oil Chemists' Society, demonstrated the importance of this distinction.
By studying 125 samples covering palm oil, olein, super olein and other liquid fractions obtained from fractionation, the researchers found that the best predictive model for cloud point was based on three variables:
The model was validated using 25 additional independent samples.
Thus, the iodine value is an important preliminary indicator, but it does not provide an adequate description of molecular composition, and on its own it does not guarantee an accurate prediction of the oil's behaviour on cooling.
The study by Zaliha and colleagues, published in Food Chemistry in 2004 and available online since 2003, provided a clear applied example of the effect of fractionation on the properties of palm oil.
The researchers used refined, bleached and deodorized palm oil (RBD Palm Oil) with an iodine value of 52 and a cloud point of 21.4°C.
After dry fractionation at 9°C, they obtained a palm olein with an iodine value of 63.1 and a cloud point of 1.6°C.
These results show how fractionation separates a proportion of the higher-melting glycerides and enriches the liquid fraction with components better able to remain liquid at low temperatures.
However, this result does not mean there is a fixed rate of change between IV and CP that applies to all raw materials; that depends on the composition of the original oil, the cooling programme and the separation efficiency.
The important industrial lesson is that cloud point can be improved with the right fractionation technology, but the relationship between the degree of improvement and the iodine value is determined by the nature of the components that were separated or retained.
An important applied study is the paper by Nor Aini and Hanirah, published in 1996 in the Journal of Oil Palm Research, entitled:
Clarity of Single and Double Fractionated Palm Oleins.
The two researchers studied samples of palm olein obtained from a single fractionation (Single Fractionated Palm Olein) and others obtained from two fractionations (Double Fractionated Palm Olein), with the aim of assessing the relationship between chemical composition, cloud point and the length of time clarity is retained during storage.
Reference table: the relationship between iodine value IV and cloud point CP
| Palm olein type | Iodine value IV | Cloud point CP |
|---|---|---|
| Single fractionated | 56 | 8.3°C |
| Single fractionated | 58 | 6.3°C |
| Single fractionated | 60 | 4.0°C |
| Single fractionated | 62 | 3.5°C |
| Double fractionated | 60 | 4.5°C |
| Double fractionated | 62 | 4.0°C |
| Double fractionated | 65 | 2.0°C |
| Double fractionated | 67 | 1.5°C |
Source: Nor Aini & Hanirah (1996), Journal of Oil Palm Research, Vol. 8, No. 2, pp. 104–112. The values are experimental results for the study samples, not a general standard conversion table between IV and CP.
Comparing the single-fractionated olein samples, we find that the rise in iodine value from 56 to 62 was accompanied by a fall in cloud point from 8.3 to 3.5°C.
Increasing IV from 56 to 58 was accompanied by a drop in CP of 2°C, while CP fell by 2.3°C when moving from IV = 58 to IV = 60.
But when moving from IV = 60 to IV = 62, the drop in CP did not exceed 0.5°C.
Therefore, the statement "every two-unit increase in iodine value lowers the cloud point by two degrees Celsius" may be valid as an approximate observation for some data points, but it is not a general scientific law.
At an iodine value of 60, the cloud point was 4.0°C for the single-fractionated olein, compared with 4.5°C for the double-fractionated olein.
At IV = 62, the values were 3.5°C and 4.0°C, respectively.
This means that repeating fractionation does not automatically guarantee a lower cloud point when the iodine value is held constant.
The same study showed differences in how long the samples retained their clarity at low temperatures, which underlines the importance of the cold test alongside the iodine value and cloud point.
In short, the table is a useful scientific tool for comparison and guidance, but it is no substitute for actual analysis of the shipment or for verifying its properties under the target storage conditions.
This is a recurring question among importers, manufacturers and quality control officers.
The accurate answer is that there is no simple, general equation of the form CP = f(IV) that allows a single iodine value to be calculated from the cloud point alone.
In the reference study above, the cloud point was 8.3°C at IV = 56 for single-fractionated olein.
If we assume the local slope of the relationship continues at this point, mathematical extrapolation may point to an iodine value of around 54–55 at a cloud point of 10°C in similar samples.
But this estimate lies outside the range of the table's direct values, and it does not represent a documented experimental result or a standard value.
A cloud point of 10°C may appear at a different iodine value owing to differences in glyceride composition, fractionation conditions or the measurement method.
This caveat becomes even more important when we know that the Codex standard for named vegetable oils (CXS 210-1999) lists an iodine value of no less than 56 among the reference characteristics of palm olein, and no less than 60 for super olein.
Therefore, the above estimate must not be turned into a judgement that the product does or does not conform.
If the cloud point is 10°C, the correct decision is to measure the iodine value directly, check the applicable specification, and then investigate the possible causes of the elevated cloud point if necessary.
Palm oils consist of a complex mixture of triglycerides (Triacylglycerols – TAGs), which differ in the types of fatty acids bound to the glycerol molecule and in their binding positions.
The most important of these glycerides include:
PPP – Tripalmitin: made up of three units of saturated palmitic acid, with a relatively high melting point.
POP: contains two units of palmitic acid and one unit of oleic acid, and affects melting and crystallization properties.
OPP/PPO: positional isomers containing the same fatty acids as POP, but bound at different positions on the glycerol.
POO/OPO: contain one unit of palmitic acid and two units of oleic acid, and therefore differ from the POP/OPP group in degree of unsaturation and thermal behaviour.
OOO – Triolein: made up of three units of oleic acid, and contributes to the oil's fluidity and relative stability at low temperatures.
A 2025 study by Hernandez Solano at the University of Liège showed that some olein and super olein samples, despite having the same iodine value, showed significant differences in cold stability at 8°C.
The study attributed these differences most likely to the POP/OPP ratio, reinforcing the importance of how fatty acids are distributed within triglyceride molecules and how this affects their crystalline ordering.
What matters is not only the number of unsaturated bonds, but also how they are distributed within the molecules that determine the oil's physical behaviour.
Crystallization is not limited to triglycerides; it is also affected by the content and composition of diglycerides (Diacylglycerols – DAGs).
The study by Siew and Ng, published in 1996, showed that the ratio of saturated to unsaturated triglycerides affects the crystallization behaviour of palm olein, and also pointed to the importance of certain diglycerides, especially 1,3-Dipalmitoylglycerol.
But the effect of diglycerides is not the same under all conditions.
Some types may promote the formation of crystal nuclei or crystal growth, while other types may affect the ordering of crystal networks or hinder their growth.
The 2025 University of Liège study observed an inverse relationship between total diglyceride content and the crystallization onset temperature within the samples it examined.
This does not necessarily contradict earlier studies, because the effect depends on the detailed molecular composition, the concentration of each type and the nature of the fat matrix.
Therefore, measuring total DAG content may not be enough to explain differences in cloud point without knowing the specific composition of the diglycerides.
Yes, and this may happen as a result of chemical or physical changes that are not necessarily reflected in the iodine value.
An important example is the study by Teh and colleagues, published in 2020 in the Journal of Oil Palm Research.
Palm olein was heated at 80 and 120°C for periods of up to 12 hours.
The results showed a gradual increase in free fatty acid content (Free Fatty Acids – FFA), together with a rise in cloud point, even though there were no significant changes in iodine value or overall fatty acid composition under the study conditions.
The results indicate that changes accompanying heating may affect crystallization behaviour without a noticeable change in IV.
But it would be wrong to generalize that higher free acidity always raises the cloud point, because the effect depends on the nature of the components, their concentration and the processing conditions.
Nor is the cloud point suitable on its own for judging oxidative or hydrolytic deterioration; independent tests such as free acidity, peroxide value and anisidine value should be used when needed.
The scientific lesson is that a stable iodine value does not guarantee that all the physical and chemical properties of the oil remain stable during processing or storage.
Crystallization is a dynamic process that depends on time, temperature and molecular composition.
It passes through two main stages:
Crystal nucleation (Crystal Nucleation): the formation of small molecular clusters that turn into stable crystal nuclei.
Crystal growth (Crystal Growth): the increase in the size and number of crystals until they are able to cause cloudiness.
With rapid cooling, supercooling (Supercooling) may occur, in which the temperature falls without crystals appearing immediately, because nucleation or crystal growth is delayed.
With slow cooling or long storage at a low temperature, there may be a greater opportunity for crystals to form and grow.
This explains why palm olein can remain clear for several hours and then turn cloudy after a day or more at the same temperature.
Yes, in the physical sense.
If the oil has previously been cooled and crystallized, and then reheated without sufficiently melting the earlier crystals, the remaining crystal nuclei may affect its behaviour on subsequent cooling.
This phenomenon is known as crystal memory (Crystal Memory).
For this reason, some industrial fractionation processes include a suitable heating stage to melt the crystalline components before the cooling programme begins.
The study by Zaliha and colleagues heated the oil to about 70°C before fractionation to erase the effect of its previous crystal history.
But this temperature is not a general requirement for all analytical methods; the sample preparation procedures specified in each method must be followed.
Hence, differences in the thermal history of a sample can lead to different results, even when the samples are taken from the same shipment.
One of the most common mistakes is treating the cloud point as a complete measure of the oil's performance during storage.
The cloud point identifies the temperature at which cloudiness appears under the test conditions, whereas the cold test (Cold Test – CT) measures how long the oil can retain its clarity at a specified temperature.
The 2025 University of Liège study showed a sigmoidal relationship between cold stability test results at 8°C and both the iodine value and the crystallization onset temperature measured by DSC.
In general, a lower crystallization onset temperature was associated with a longer clarity retention time.
But this relationship does not make the cloud point a substitute for the cold test.
To illustrate, imagine two samples with the same iodine value but differing in glyceride composition and crystallization kinetics.
The first sample may remain clear for longer at a low temperature, while the other begins to cloud early.
This difference cannot be explained by the iodine value alone; it requires a study of glyceride composition and of nucleation and crystal growth times.
So the important question is not only: at what temperature does the oil turn cloudy? But also: how long can it stay clear at that temperature?
Dry fractionation (Dry Fractionation) relies on the controlled cooling of palm oil to crystallize part of the higher-melting glycerides, which are then separated from the liquid fraction.
The process produces:
Olein (Palm Olein): the relatively more fluid liquid fraction.
Stearin (Palm Stearin): the solid fraction, higher in high-melting glycerides.
Fractionation efficiency is affected by the composition of the crude oil, the cooling rate, crystallization time, agitation conditions, crystal size and shape, and filtration efficiency.
Cremer and colleagues studied in 2023 the effect of four levels of fully saturated triglycerides (StStSt): 7.0%, 7.6%, 8.2% and 9.8%.
The results showed that the matrix containing 7.6% crystallized fastest under the study conditions, and gave an olein with a higher-than-expected yield, iodine value and cloud point.
The analysis also revealed an unusual enrichment in OPP and a reduction in OPO.
The results confirm that industrial crystallization behaviour is not determined by overall saturation alone, but by the detailed glyceride composition and the operating conditions.
Fractionation plants seek to achieve two goals that may conflict:
First: producing an olein with high cold stability.
Second: achieving the highest possible yield of the liquid fraction.
But obtaining a low cloud point olein may require separating a larger proportion of high-melting components, which often leads to a lower olein yield and a higher proportion of stearin.
The study by Zhang and Lim, published in 2024, used neural network and genetic algorithm techniques to optimize industrial crystallization conditions.
The study's results showed the following:
| Target cloud point | Yield |
|---|---|
| CP 6°C | 63% |
| CP 8°C | 74% |
| CP 10°C | 77.26% |
These values are the study's results under the operating conditions it examined, and do not represent fixed yields for all fractionation plants.
The results reflect an important economic trade-off between lowering the cloud point and increasing yield.
Therefore, the best industrial choice is not always to produce olein with the lowest possible cloud point, but to produce the grade that meets market requirements with the highest technical and economic efficiency.
Blending palm olein with some vegetable oils that are higher in unsaturation may improve its fluidity and relative cold stability.
But the effect is not necessarily linear with the iodine value.
Adding another oil changes the glyceride composition of the blend and may lead to physical interactions between the different glycerides that affect crystal formation and growth.
Studies on blending palm olein with sunflower oil and high-oleic safflower oil have shown improved cold stability in some blends, to varying degrees depending on the blending ratios and the composition of the components.
New blends should therefore be evaluated through cloud point, the cold test, solid fat content and oxidative stability, alongside the applicable standards and food labelling requirements.
No oil blend may be marketed under the name of pure palm olein.
The clear scientific answer: no, not necessarily.
Palm olein is a mixture of glycerides with different melting points, and some of its components may crystallize naturally when the temperature drops.
The appearance of cloudiness or white crystalline deposits as a result of this crystallization is a physical change that does not, on its own, mean rancidity, spoilage or adulteration has occurred.
The cloudiness may disappear when the oil is warmed enough to allow the crystals to dissolve.
However, a distinction should be made between natural clouding caused by crystallization and cloudiness arising from contamination with water, impurities or other causes.
Three concepts must also be kept separate:
Food safety: concerns the oil being free from hazards that affect consumer health.
Chemical quality: concerns indicators such as free acidity, peroxide value and oxidation products.
Functional quality: concerns how well the oil suits the intended use, including its ability to stay clear during storage and handling.
An oil may be sound in terms of food safety and chemistry, yet fail to meet the cold stability requirements set out in the supply contract.
It is wrong to regard all cloudiness as evidence that the oil has spoiled, just as it is a commercial mistake to ignore clarity requirements if they are part of the agreed specifications.
Professional quality management of palm olein requires moving from reliance on a single iodine value to an integrated system that combines chemical analysis, physical testing and industrial control.
The practical measures can be summarized as follows:
The published table can be treated as a guidance tool for initial screening and interpreting results, not as a final acceptance or rejection tool.
For example, if an olein shipment arrives with an iodine value of 60 and a cloud point that is unusually high compared with the plant's experience, it should not be judged non-conforming directly on the basis of the table.
Instead, it is preferable to follow a technical sequence that starts by verifying the measurement method and sample preparation, then reviews the iodine value and cloud point results, carries out the cold stability test, and then moves on to glyceride analysis or a study of manufacturing conditions if the differences persist.
In this way, reference data become a tool for guiding inspection and analysing the causes of differences, not a substitute for actual measurement.
Recent studies point to the possibility of developing statistical and predictive models that link cloud point to iodine value, glyceride composition, solid fat content and operating conditions.
Artificial intelligence techniques can also be used to optimize cooling curves and fractionation programmes and to increase production efficiency.
But the success of these models depends on the quality of the data they were built on and how well that data represents the target raw materials and industrial conditions.
A model developed using samples from one plant may not give the same accuracy at another plant that differs in the nature of its oil or its fractionation technology.
That is why models should be validated using independent samples and actual operating data before they are used to make industrial decisions.
The aim is not to do away with the laboratory, but to turn its data into predictive knowledge that helps improve quality, reduce losses and increase production efficiency.
This property is of practical importance in the Egyptian and Arab markets because of the differences in storage and handling conditions between summer and winter, and the variety of palm olein grades imported and used in manufacturing and packing.
A shipment may conform to chemical quality indicators but fail to achieve the required level of clarity during winter storage.
On the other hand, insisting on an unnecessarily low cloud point may increase the cost of the raw material or of manufacturing, because of the lower yield during fractionation.
Hence the importance of aligning market requirements with the functional properties of the product.
This requires stronger cooperation between importers, manufacturers, quality laboratories and standards bodies, in order to identify the olein grades suited to the conditions of use and storage, standardize measurement methods and develop contractual specifications.
Spreading scientific awareness of the nature of crystallization also helps reduce commercial disputes and misinterpretation of the phenomenon of oil clouding in winter.
Sound scientific quality management does not always mean buying or producing olein with the lowest possible cloud point, but choosing the grade that meets the requirements of use with the best balance between quality, cost and climatic suitability.
In the oils and fats industry, not every fact is written on the certificate of analysis, and not every product with similar numbers performs identically.
This is what the cloud point of palm olein reveals.
Behind a clear drop of oil lies a complex system of triglycerides, diglycerides, positional isomers, molecular interactions and mechanisms of nucleation and crystal growth that control how the oil responds to falling temperatures.
Scientific studies have demonstrated an important inverse relationship between iodine value and cloud point as a general trend, but they have also confirmed that this relationship is not fixed or linear, and that it is not enough on its own to predict the oil's behaviour accurately.
Nor does the cloud point replace the cold stability test: the first tells us the temperature at which cloudiness appears, while the second reveals how long the oil retains its clarity.
From an industrial perspective, improving cold stability may require further fractionation, with the accompanying lower yield and higher cost.
Modern quality management of palm olein should therefore be based on integrating molecular composition, crystallization kinetics, manufacturing conditions, laboratory tests and market requirements.
The iodine value tells us the degree of unsaturation, the cloud point reveals one aspect of the oil's response to cold, and the stability test determines how long it stays clear; a sound scientific judgement can only be reached by reading these indicators together.
Perhaps the message that should stay in the mind of every specialist, manufacturer and importer is:
"The quality of palm olein lies not in what the analysis numbers say alone, but in what the oil's behaviour reveals when the cold puts it to the test; the numbers describe the components, but crystallization reveals how they behave."