Infused olive oil is olive oil that has been infused with herbs, spices, or other ingredients to add flavor. It has become a popular ingredient in many recipes and for dipping bread. However, infused olive oil does not last forever and will eventually go bad. There are a few key reasons why infused olive oil goes rancid over time.
Olive oil’s natural tendency to go rancid
All olive oils have a natural tendency to go rancid over time. This is due to the chemical composition of olive oil. Olive oil is very high in monounsaturated fats, particularly oleic acid. Monounsaturated fats are more stable than polyunsaturated fats but they still readily oxidize and go rancid [1]. Exposure to oxygen, light, and heat speeds up this oxidative process. The chlorophyll in extra virgin olive oil also accelerates rancidity development [2].
So even without any added flavors, plain olive oil stored at room temperature will naturally go rancid within 6-12 months. The addition of herbs, garlic, chilies and other flavorful ingredients only serves to make the oil go bad quicker.
Water content in infused olive oils
Many infused olive oil recipes call for the addition of fresh herbs, fruits, vegetables or other plant material. These contribute extra water and moisture to the oil. The increased water content provides the perfect breeding ground for bacteria, mold and other microbes that can flourish in the anaerobic (oxygen-free) environment of an oil [3].
As these unwanted microorganisms proliferate, they accelerate the oxidation and hydrolysis of the oil, leading to quicker rancidity. Garlic, being a vegetable with very high moisture, is particularly problematic. The water it releases mixes into the oil, so garlic infused olive oil has a shorter shelf life than other herb infused oils.
Lack of preservatives
Off-the-shelf olive oils are purified and contain antioxidants and antimicrobial preservatives that help prevent rancidity. In contrast, homemade infused olive oils are raw and contain no added preservatives.
Antioxidants like ascorbic acid, citric acid and sodium erythorbate are commonly added to store-bought oils. They retard oxidation and staving off rancidity development in the oil [4]. Antimicrobials such as potassium sorbate and sodium benzoate prevent microbial growth. Without these preservative additives, infused olive oils made at home spoil quicker.
Best practices for extending shelf life
While infused olive oil is perishable by nature, you can take some steps to maximize its freshness:
- Use the freshest, highest quality olive oil possible
- Opt for an extra virgin olive oil with low acidity
- Start with herbs/garlic/spices with very low moisture content
- Use dried herbs/spices rather than fresh
- Make smaller batches and store in fridge
- Never store at room temperature
- Always use clean, sterile equipment and containers
- Add a pinch of salt or vitamin E to help stabilize
Following these best practices, infused olive oil can stay fresh in the refrigerator for 2-3 months. Unrefrigerated, the shelf life drops down to just 1-2 weeks.
Signs that infused olive oil has gone bad
Here are some common signs that your infused olive oil is past its prime:
Change in color
Fresh olive oil is a bright green color. As it oxidizes, it darkens to a gold, then deeper orange-brown hue. A dull or muddy looking color signals degradation.
Off odors
Rancid olive oil gives off a unpleasant, stale, grassy smell. You may also detect odors of old nuts or crayons. If it smells odd, it’s likely gone off.
Change in texture
Good olive oil should have a smooth, consistent liquid texture. Oil that has gone rancid may become sludgy or grainy.
Smoke point changes
The smoke point of rancid oil decreases. If your infused olive oil smokes up at a lower temperature than usual, it’s a sign of spoilage.
Mold growth
Visible mold colonies may appear if the oil has sufficient water activity for fungal growth. This is very common with garlic infused olive oil.
| Signs of Rancidity | Description |
|---|---|
| Color Change | Dull, dark, muddy color instead of bright green |
| Off Odors | Stale, grassy, nutty or crayon-like smell |
| Texture Change | Grainy or sludgy instead of smooth |
| Lower Smoke Point | Smokes at lower temperatures than normal |
| Mold Growth | Visible mold colonies or fuzz |
Health risks of rancid olive oil
Rancid olive oil not only tastes bad, but it can also be bad for your health. Here are some of the potential health risks:
1. Formation of harmful free radicals
When olive oil oxidizes, it forms pro-inflammatory compounds like aldehydes, peroxides and free radicals [5]. Ingestion of these can cause oxidative stress and damage to cells.
2. Reduced antioxidant content
Antioxidants like polyphenols and vitamin E degrade as olive oil goes rancid. You miss out on these healthy micronutrients.
3. Gastrointestinal irritation
Spoiled oils contain irritating breakdown products. These can cause nausea, vomiting and diarrhea if consumed [6].
4. Nutrient deficiencies
Rancid oils can interfere with the absorption of fat-soluble vitamins A, D, E and K. Deficiencies in these vitamins can cause adverse effects.
5. Allergic reactions
Microbial growth and oxidation create compounds not originally present in the oil. These may provoke new allergic responses in sensitive individuals.
So using up infused olive oil promptly helps avoid these negative health impacts of rancidity. Discard any leftovers that show signs of spoilage.
Should you consume infused olive oil past its shelf life?
It is not recommended to consume infused olive oil that is past its prime. Rancid olive oil has an unpleasant bitter taste and offers no nutritional benefits. At worst, it may provoke vomiting or diarrhea if eaten.
That said, rancidity is not necessarily an immediate health hazard. Eating a small amount of expired infused oil is unlikely to make you acutely sick. But for optimal nutrition and flavor, it is best to stick to olive oil within its recommended 3 month shelf life. Discard any older, more degraded oil.
How to store infused olive oil properly
To optimize the shelf life of your infused olive oils:
Keep it cool
Refrigeration is ideal for infused oils. The cooler temperature retards oxidation and microbial growth. Aim to store around 40°F.
Minimize oxygen exposure
Limit headspace in storage containers. Displace air with an inert gas like nitrogen if possible. Oxygen is required for oxidative rancidity.
Avoid light
Store infused oils in tinted or opaque containers. Light fuels oxidation reactions and breakdown of the oil.
Control moisture
Only add very dry herbs/spices when infusing. Check for condensation in the bottle. Excess moisture quickens spoilage.
Cleanliness
Sterilize equipment and bottles well.Dirty containers inoculate oil with bacteria and mold.
Following these tips, your infused olive oil will stay fresher for longer. Discard any batches that show signs of aging like changes in smell, taste, appearance or texture.
Frequently Asked Questions
Why does my garlic infused olive oil get moldy?
Garlic contains more innate moisture than dry herbs and spices. This moisture allows mold to grow. Refrigeration inhibits mold growth by slowing metabolism. Smaller batches in sterile jars also reduces risk.
Can you extend the shelf life by adding preservatives?
Yes, adding antioxidants like vitamin E or antimicrobials like potassium sorbate when preparing the infused oil will help extend its freshness. But this also gives it more of an “unnatural” processed quality.
What are the best herbs/spices to infuse olive oil with?
Dry herbs and spices with low moisture content are ideal. Good options include crushed red pepper, dried oregano, rosemary, thyme and chili flakes. Avoid fresh garlic and basil.
Is rancid olive oil safe to cook with?
No, rancid oil has degraded too much to be suitable for cooking. The altered structure can also produce harmful compounds when heated to frying temperatures.
How long does infused olive oil last unrefrigerated?
At room temperature, infused olive oil will go rancid within 1-2 weeks. For optimal freshness and shelf life beyond 2-3 weeks, it must be refrigerated.
The bottom line
Infused olive oil has a shorter shelf life than regular olive oil due to its added flavors and water content. Lack of preservatives also leads it to deteriorate faster. Properly stored infused olive oil lasts 2-3 months refrigerated. Any oil showing signs of rancidity like smell, taste, color, texture and smoke point changes should be discarded. Consuming rancid oil provides no benefits and potentially negative health effects. Following best practices for storage, preparation and vigilant monitoring of quality helps maximize the shelf life of your infused olive oils.
