How to spot adulteration in cooking oil? Tips & tricks

Adulteration of cooking oil is a common practice aimed at increasing profits by diluting or altering the oil with cheaper or lower-quality substances.

Here are some of the most common adulteration techniques:

Palm oil or palm kernel oil: Often mixed with more expensive oils like olive oil, sesame oil, or mustard oil to reduce costs.

Mineral oil: Sometimes added to edible oils, though it's not safe for consumption.

Rice bran oil: Used to adulterate more expensive oils like groundnut or sesame oil due to its lower cost.

Soybean oil: Commonly used to adulterate other vegetable oils like sunflower or safflower oil.

Sudan red dye: A synthetic dye used to colour oils to make them appear more appealing or of higher quality. It's carcinogenic and banned for use in food products.

Artificial flavouring: Added to low-quality oils to mimic the taste of more expensive oils like sesame or olive oil.

Old or rancid oil: Mixed with fresh oil to reduce waste, though it can affect the taste, smell, and safety of the product.

Used cooking oil: Recycled and mixed with fresh oil, which can introduce harmful compounds formed during the initial cooking process.

Hexane or other solvents: Used to extract more oil from seeds and then mixed with the final product, though residues of these solvents can remain in the oil.

Starch: Added to oils like coconut oil to increase its volume, though it can alter the texture and appearance.

Bleaching and deodorizing: Low-quality oils may be over-refined, bleached, or deodorized to remove odours and colours that indicate poor quality. This process can strip the oil of its nutrients and natural flavour.

Hydrogenated oils: Some oils may be partially hydrogenated and then mixed with liquid oil to improve shelf life and texture, which can introduce trans fats.

These techniques not only degrade the quality of the oil but can also pose significant health risks, making it essential to be vigilant when purchasing and using cooking oils.

Detecting adulteration in cooking oil can be challenging, but there are a few methods you can use at home to spot potential issues:

Clarity
Pure cooking oil is usually clear. If the oil appears cloudy or has sediment at the bottom, it may be adulterated.

Colour
Unusual or uneven colouring might indicate contamination or the presence of other oils.

Unusual smell
Pure oils have a specific, natural aroma. If the oil smells rancid, metallic, or off, it could be adulterated or old.

Taste
If the oil tastes different from usual, it might be mixed with other substances. However, tasting should be done cautiously and in very small amounts.

Burning test
Heat a small amount of oil in a pan. Pure oil has a typical aroma when heated, but adulterated oil may emit an unusual or unpleasant odour.

Refrigeration test
Place the oil in the refrigerator for a few hours. Pure coconut or olive oil will solidify at lower temperatures, while adulterated oils might remain liquid or partially solidify.

Blotting paper test
Place a few drops of oil on blotting paper or a plain white sheet of paper. Pure oil will spread uniformly without leaving any residues. Adulterated oil may leave stains or traces of other substances.

Soap test (for coconut oil)
Mix 2 ml of coconut oil with 2 ml of caustic soda (sodium hydroxide) solution and 1 ml of water. If the oil turns into a soap-like paste, it's pure. Adulterated oil may not form a proper paste.

Simple chemical tests

Iodine test: Add a few drops of iodine to the oil. If it turns purple, it indicates the presence of starch or other adulterants.

Sudan red test: This is more technical and requires a chemical lab setting. It tests for the presence of synthetic dyes used to color the oil.

Lab testing

For a definitive result, you can send a sample to a lab for analysis. They can detect even trace amounts of adulterants.

Purchasing tips
Buy from reputable brands and avoid very low-cost options. Ensure the oil is certified and check for any additives listed on the packaging.