You know that bottle of hoisin sauce in your fridge door? The one you bought for a stir-fry recipe in 2022? Yeah. We need to talk about that.

I used to treat the refrigerator like a time-freezing machine. Ketchup, mustard, soy sauce, hot sauce — they all went in after opening and stayed there until they were empty, whether that took three months or three years. Then I got food poisoning from a Thai peanut sauce that had been open for… I do not actually know how long. Long enough that the label had started peeling off.

After that experience, I actually looked up how long opened sauces last. The answer is more complicated than I expected because not all sauces are created equal.

The General Rules

Most opened condiments fall into one of three categories based on their acidity, sugar content, and salt level. These three things are natural preservatives.

High-acid sauces — things like ketchup, mustard, hot sauce, and vinegar-based barbecue sauce — are hostile environments for bacteria. They can last six months to a year in the fridge after opening. The color might darken and the flavor might fade, but they are unlikely to make you sick.

Oil-based sauces — pesto, chili oil, mayonnaise — are riskier. Oil can go rancid, and mayo in particular is an emulsion that can separate and spoil. These should be used within one to two months.

Creamy or low-acid sauces — Alfredo, cheese sauce, anything dairy-based — are the most perishable. Use within three to five days. Do not push your luck with these.

Specific Timelines I Actually Follow

• Soy sauce: Basically forever. The salt content is so high that nothing can grow in it. I have had the same bottle for eighteen months. Still fine.
• Fish sauce: Same deal. Salt preserves it indefinitely. It might develop sediment at the bottom — that is normal.
• Ketchup: Six months in the fridge. The vinegar keeps it safe, but the tomato flavor degrades over time.
• Mustard: A year, easy. Mustard seeds contain antimicrobial compounds.
• Mayonnaise: Two months after opening. The store-bought stuff is pasteurized and acidic enough to last longer than homemade, but do not push past two months.
• Salad dressing (vinaigrette): Three to four months. The oil may solidify in the fridge — run the bottle under warm water.
• Salad dressing (creamy): One month. Ranch, blue cheese, Caesar — shorter shelf life because of the dairy and egg components.
• Pesto: One week. Maybe two. I freeze leftover pesto in ice cube trays now because I got tired of throwing away half-eaten jars.

The Smell Test Is Not Enough

I used to think if it smelled fine, it was fine. That works for milk but not for everything. Some foodborne pathogens do not produce obvious odors. When in doubt, check the timeline. If the sauce has been open longer than the guidelines above, spending three dollars on a new bottle is cheaper than a night in the bathroom.

Also, do not eat directly from the jar. Double-dipping with a spoon introduces bacteria from your mouth. Pour what you need into a separate dish.