There are certain subjects that, once brought up in conversation, get people riled up lightning-fast ― and how to store condiments is probably near the top of that list.

For real, who hasn’t ended up in an all-out brawl over whether the peanut butter should be refrigerated or reconsidered a friendship after finding out your buddy stores ketchup in the pantry?

Condiment conundrums are nothing new, but there are general rules of thumb to keep in mind whenever you’re unsure where to keep the ranch dressing.

“Condiments that must be refrigerated after opening have specific characteristics that make them more susceptible to bacterial growth when they’re left out at room temperature,” said Katie Heil, a certified professional in food safety and senior editor at StateFoodSafety.

These characteristics include high levels of carbs and protein, a neutral or slightly acidic pH, and moisture. By contrast, condiments that don’t need to be refrigerated typically contain more fats, which are almost impenetrable to bacteria and keep them from growing to unsafe levels.

The easiest way to remember? If a condiment is thin enough to easily flow to the head of the bottle when you turn the bottle upside down, refrigerate it. “Chances are, it doesn’t contain enough fat to be shelf-stable,” Heil said. 

On the other hand, if the condiment is so thick that it takes a while to fall to the head of an upside-down bottle, it probably contains enough fat to be shelf-stable.

When in doubt, check the label. “The Code of Federal Regulations states that any products that ‘require special handling to maintain their wholesome condition’ must have those instructions prominently displayed on the product,” Heil said, including messages like “Keep refrigerated” or “Refrigerate after opening.”

Now let’s get to some specific guidance.

Ketchup

The verdict: Refrigerate.

Ketchup is acidic and concentrated, so it’s not imperative that you store it in the fridge and you can generally let it sit out for up to one month before it starts to turn rancid. Heinz ketchup, for example, is acidic enough to be considered shelf-stable.

But some other brands of ketchup don’t have a high enough acidity level to prevent bacterial growth. “Because the average consumer won’t know the pH levels of their preferred ketchup brand, it’s recommended to refrigerate all ketchup after opening, just to be safe,” Heil said. Homemade or unprocessed ketchup should always be refrigerated.

Besides, “refrigerating ketchup after it’s been opened doesn’t just extend its shelf life — it helps to maintain its colour and taste too,” said Eric Sieden, director of nutrition and food services for Glen Cove, Plainview and Syosset Hospitals in New York.

Mustard

The verdict: Refrigerate.

Mustard also doesn’t need to be refrigerated because of its acidity, but like ketchup also benefits from being in the fridge.

“Without refrigeration, mustard can last up to one month, but in the fridge, it can last up to a year,” Sieden said. “Plus, mustard that’s not refrigerated has a tendency to dry out and separate. It fares better when stored in dark and cool places.”

Mayonnaise

The verdict: Refrigerate.

Since mayo contains eggs, it should always be stored in the fridge to prevent bacterial growth. Doing so can also extend its shelf life to a few months, Sieden said.

Barbecue Sauce

The verdict: Refrigerate.

“Barbecue sauce is very similar to ketchup in that it’s highly acidic, due to the vinegar and salt in its ingredients,” Sieden said. That keeps it pretty safe from bacterial growth.

Although it’s not necessary to store barbecue sauce in the fridge, it lasts much longer if you do. Refrigeration can also better maintain its colour and texture, Sieden said.

Jam And Jelly

The verdict: It depends.

Though the jars say to refrigerate after opening (to prevent fungal growth), jams and jellies don’t need to be refrigerated if they’re going to be used within one month.

“Refrigeration can extend its shelf life by a few months, but because jam has a pH level of 3 (bacteria grows most in pH levels of 6.5-7), there’s no harm in storing it in your pantry,” Sieden said.

Butter

The verdict: It depends.

Storing pasteurised butter in the fridge will extend its shelf life, but keeping it on the counter is also OK for shorter periods. “Pasteurised butter contains at least 80% fat, which helps prevent bacterial growth,” Heil said. “It’s even less vulnerable to bacterial growth if it’s salted.”

If you do decide to store it on the counter, Heil recommends keeping it in a covered dish and eating it within 10 days to ensure the best quality. (Other sources have said no longer than one week.) Homemade or unpasteurised butter, on the other hand, should always be refrigerated. 

Nut Butters

The verdict: It depends.

If the peanut or other nut butter has been commercially processed, it can be stored in a cool, dry place outside the fridge for three to six months. But if it’s homemade or “natural,” it should be refrigerated.

“Nut butters, like peanut butter, typically contain a lot of fat, which helps prevent bacterial growth,” Heil said. “The commercial manufacturing process kills any bacteria that may be in the ingredients, so the nut butter starts — and stays ― relatively bacteria-free.”

But if it’s homemade, put it in the fridge just to be safe. “Homemade nut butter doesn’t go through the same process, so it’s likely to start with a higher level of bacteria,” Heil explained. “If you store it in the fridge, where the cold temperature can help prevent bacterial growth, it will last a lot longer.”

Ditto for store-bought natural peanut butter ― the kind where you have to keep stirring the peanut oil and solids back together. They only last outside the fridge for up to one month before those oils begin to turn rancid.

Nut Oils

The verdict: It depends.

Nut oils with high levels of monounsaturated fats, like coconut and peanut oils, are considered shelf-stable, while those that are higher in polyunsaturated fats, like walnut oil, should be refrigerated.

“Polyunsaturated fats reportedly don’t help prevent bacterial growth to the same degree monounsaturated fats do,” Heil said.

Nut oils start to turn rancid once they’re exposed to oxygen, light and heat, so you should store even shelf-stable picks in a cool, dark cupboard.

And when you pop less stable nut oils in the fridge, beware that “low-temperature storage can cause oils to become cloudy or solidify,” said Tony Johnston, a food safety expert and professor at the School of Agriculture at Middle Tennessee State University. Once you take them back out and let them warm up, most of the cloudiness or solid particles will become liquid again.

Vinegar

The verdict: Don’t refrigerate.

“Vinegar is acetic acid, and there are very few microorganisms that can attack it,” Johnston said. “For all practical purposes, it doesn’t need to be stored in the fridge.”

Salad Dressings

The verdict: Refrigerate.

Yes, salad dressings typically contain a lot of vinegar, but they also contain oil and other less stable ingredients. “The oil will oxidise and become rancid over time, so for quality control and extension purposes, it’s strongly recommended that dressings be stored in the fridge,” Johnston said.

Heed this warning even more if the dressing in question contains cream, yogurt or mayonnaise. “The rule of thumb is if the individual ingredients are something you would refrigerate normally, you should do the same when they’re in a product like this,” Sieden said.

Soy Sauce

The verdict: It depends.

Soy sauce is a product of fermentation and is highly concentrated, which means it doesn’t necessarily require refrigeration. 

It has a very long shelf life without refrigeration ― it holds its quality for up to one year, Sieden said ― and most manufacturers simply recommend keeping it in a cool, dry place.

“The only issue is flavour change over time,” Johnston said. “If a person doesn’t use it very often, refrigeration will slow down the rate of flavour change.”

Honey

The verdict: Don’t refrigerate.

Honey is another highly concentrated product that naturally resists spoilage, so it doesn’t have to be refrigerated. In fact, if it’s stored in the fridge, Johnston said, “it will become very thick and may accelerate the rate at which it solidifies.”