Like most edible stuff, truffle oil is also prone to spoilage (even if flavored with synthetic compounds and not real truffles). But the shelf life depends on various factors.
Truffle oil is made by infusing a base oil like extra virgin olive oil with lab-made truffle essence. Some varieties have real truffle too, but in tiny quantity.
An opened bottle of commonly sold truffle oil (made with artificial flavors) can last around 10 to 12 months. But the following factors can affect the shelf life.
Exposure to light, heat, humidity and air can cause rapid deterioration due to oxidation, bacterial growth and/or mold development.
Oils made with real truffles have short shelf life due to moisture exposure and potential contamination. In contrast, synthetic-flavored oils are more stable and longer-lasting.
Dark/tinted glass bottles provide better protection against any degradation caused by light.
Contact with water or other food can introduce contaminants. So it's important to use clean, dry utensils if they come in contact with oil within the jar/bottle.
If the carrier oil used in production has already aged to some extent, it will of course turn rancid sooner.
The more you open the bottle to use the oil, the more it gets exposed to air. And that can accelerate oxidation and spoilage.
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