How long should cooking oil be used after opening?

Normally, the shelf life of popular cooking oils on the market when unopened is from 18 to 24 months, according to the website. HK01. However, the time stamp printed on this bottle label only applies to cases where the oil tank is completely sealed and completely isolated from the air. It absolutely does not mean that after opening the oil, it can still be left for that long without degrading.

Once the oil tank has been opened and exposed to air, the fatty acids in the oil will continuously undergo an oxidation reaction with oxygen. This process causes the oil to become rancid and degrade over time, and also produces by-products that are harmful to the human body such as peroxide, aldehyde and ketones.

4 warning signs that cooking oil has completely degraded

If cooking oil stored at home shows the following clear signs, it proves that the oil has seriously deteriorated and should absolutely not be used again:

• Strong smell: An oily, burning or rancid smell appears, causing obvious nasal irritation.

• Change status: The oil, which was originally transparent and shiny, became cloudy; residue appears at the bottom or a clear top-bottom layer.

• Abnormal taste: When tasted, it has an unusually bitter and astringent taste.

• Loss of scent: The oil completely loses its natural fragrance.

How long does it take for cooking oil to deteriorate after opening?

Related research data shows that, with the popular 5-liter large bottled cooking oil, in the condition of opening and closing the lid daily for use, only on the 42nd to 63rd day, the peroxide index (oxidation index) has exceeded the safety standard. Even for a small 1 liter bottle, after opening and using for 28 to 56 days, the peroxide index will exceed the safety threshold.

Based on a large amount of experimental data, experts in the field of food and nutrition give clear advice:

• Large bottle of cooking oil (5 liters): It is best to consume within 42 days after opening.
• Small bottle of cooking oil (1 liter): Try to use it all within 28 days of opening.

This is to minimize cooking oil’s long-term exposure to air, leading to oxidation and deterioration.

The danger of long-term accumulation of toxins

Doctors also issued a warning that if you accidentally ingest denatured oil with a peroxide index that exceeds the standard a few times, a normal adult’s metabolism can completely eliminate it, and the body will not experience serious damage immediately.

However, if you eat this substandard oil continuously from day to day, from month to month, the damage that accumulates over time will continuously irritate the lining of the digestive tract. This can easily lead to unpleasant symptoms such as nausea, vomiting, abdominal pain, diarrhea, and long-term tolerance will certainly lead to many other potential health risks.