We’ve all seen the research: A little olive oil a day keeps the doctor away. But what happens to those health benefits once oil turns rancid? Once exposed to high oxygen levels, all types of oils’ vital fat molecules degrade. This process results in a filthy looking, tasting, and smelling product — good for nothing but the bin. If you accidentally consume expired oil once, it’s unlikely to cause immediate damage. However, it’s best to avoid making this a frequent mistake. Repeated consumption of expired bottles increases your risk of Alzheimer’s, diabetes, and cancer.
It boils down to science. When oil spoils, it forms free radicals on a molecular level. Rather than having stabilized molecules, these atoms have tiny electrons that break off and stray. The desperate molecule left behind becomes a thief, damaging human cells as it attempts to steal electrons and rebalance. Because of this, free radicals cause oxidative stress when entering our bodies. If you don’t yet know the spoilage signs, it’s definitely time to learn how to tell when your oil has gone bad. It should be clear when oil has gone rancid, by a bitter taste, off smell, and darker color.
Speaking of signs, do you know that certain oils also release free radicals when heated past their smoke point, as well as when they’ve gone rancid? Be wary of which types you select for cooking. Seed-based products (like sunflower) are notoriously high-risk. Olive oil seems to be safer; while its smoke point does depend on the specific oil, it shouldn’t reach danger point until about 405 degrees Fahrenheit.
How long does oil last for?
With the dangers of rancid oil established, the next burning question is how long bottles will safely last? Nobody wants spoilage on their hands — especially after learning about free radicals. Always abide by the labeled expiry date. Generally, oil is okay stored for up to two years unopened and best used within six months once you crack that cap. But there are exceptions.
It is important to acknowledge variations in the shelf-life of oil types. Answering the question of how long does olive oil last after it’s opened is different from researching when to use sunflower or vegetable bottles. Olive oil lasts up to three years unopened, sunflower oil up to two, and vegetable oil just a year. Anything that undergoes refinement during processing (typical for seed and vegetable-based products) is already slightly destabilized due to heat exposure — starting the shelf-life clock ticking early.
Lengthy storage isn’t the only culprit behind rancidification, either. Improper storage risks a premature demise for any new bottles of freshly-purchased oil. Keep products in cool, dark conditions and never decant from original containers. And if you’re wondering what happens if you refrigerate cooking oil, it can actually help extend the lives of recipes hinged on polyunsaturated fats. Any fish or particularly delicate nut oils? Pop them in the fridge. Other oils, like olive or vegetable, sit safely in a darkened pantry.
