Mayonnaise. You may buy mayonnaise off a non-refrigerated shelf, but the second you pop the top, you must put it in the refrigerator. In fact, the USDA recommends opened mayo be tossed in the trash if its temperature reaches 50 degrees or higher for more than eight hours.
Like all items that require refrigeration (including leftovers), mayo has a two-hour rule. The USDA recommends not leaving mayo out at room temperature for more than two hours before moving it back into the fridge.
Commercially produced mayonnaise, as opposed to the homemade version, does not need to be refrigerated, according to the report. Food scientists find it's because mayo undergoes strict testing and "its acidic nature slows the growth of the bacteria associated with food-borne illnesses,'' according to NPD Group.
Another reason why mayonnaise needs to be refrigerated especially after it's been opened is the fact that the containers are usually vacuum sealed. It's also been sterilized. This means that any air that the mayo is exposed to once opened contaminates the mayo and can lead to it starting to spoil.
At room temperature, mold and bacteria growth resumes almost immediately, and warmer temperatures can lead to an explosion of growth that rapidly degrades the food product.
Common condiments that don't require refrigeration include soy sauce, oyster sauce, fish sauce, honey and hot sauce. Feingold says vinegars and olive oil (stored in a cool, dark place) are pantry-bound; coconut oil is actually best kept out of the fridge since it hardens below room temperature.
Some classic condiments should go in the fridge once you've opened them, like mustard, mayonnaise, and ketchup. While mustard doesn't really go bad, per se, it loses much of its flavor after about a year in the fridge. Opened containers of mayo and ketchup, on the other hand, can go rancid after six months.
The perishable nature of mayonnaise is also why you should throw out mayo that's been left out unrefrigerated overnight. It could be totally fine—until you get food poisoning. And, in general, the FDA recommends tossing perishable foods, including mayo, that have been left out at room temperature for two or more hours.
After opening, however, it is strongly recommended to refrigerate Kewpie mayonnaise for fear that it may get contaminated through exposure to air that carries bacteria and contaminated utensils.
Do Fresh Eggs Need to Be Refrigerated? Freshly laid eggs need to be refrigerated immediately. Fresh eggs purchased from a farmers market need to be refrigerated as soon as you get home. Per USDA guidelines, eggs should be stored at 40 degrees F or below to help minimize the risk of Salmonella.
According to the USDA, butter is safe at room temperature. But if it's left out for several days at room temperature, it can turn rancid causing off flavors. The USDA does not recommend leaving it out more than one to two days.
An open jar of peanut butter stays fresh up to three months in the pantry. After that, it's recommended to store the peanut butter in the fridge (where it can maintain its quality for another 3-4 months). If you don't refrigerate, oil separation can occur.
Before it's opened, a jar of mayo will last in the pantry for about three months. If you just opened a jar, know that it should be stored in the refrigerator and used within two months. However, if you make homemade mayonnaise, it will last only up to a week in the fridge—so make plans to use it all up before then.
In terms of safety, there's no real need to refrigerate ketchup. Tomatoes and vinegar, the main components in ketchup, help preserve the condiment at room temperature due to their natural acidity.
Condiments such as ketchup and mustard
According to TheKitchn.com, yellow, Dijon, or even whole-grain mustard can be put away in the cabinet for up to two months and as mentioned before, ketchup can be kept outside the refrigerator for up to a month.
Look for mold growth, a color change, and a bad smell
Mold growth, a change in color, and an unpleasant smell are three indications that your mayo has gone bad. According to the Department of Health of New York State, molds can grow anywhere that moisture is present, which is why they can thrive in mayo.
But, like many shelf-stable foods, that jar of mustard “should still be kept in the fridge after opening to prolong the complexity, heat, and flavor.” Collins also notes that “as mustard sits and is opened and closed and taken in and out of the fridge, the flavor will change…so while it doesn't go bad like a fish or ...
Well, mayonnaise contains an extra substance, called an emulsifier, which is used to unite the two immiscible ingredients to form a stable, usable emulsion. The emulsifier is made from a hydrophilic (water-loving) head and a hydrophobic (water-hating) tail, which work together to stop the oil from separating out.
Many people with mild cases of food poisoning think they have stomach flu. The time it takes food poisoning symptoms to start can vary. Illness often starts in about 1 to 3 days. But symptoms can start any time from 30 minutes to 3 weeks after eating contaminated food.
The U.S. Department of Health doesn't recommend keeping any perishable food sitting out of the fridge for more than two hours — and that's certainly the case for soft cheeses, like cottage or cream cheese, brie, or fresh mozzarella.
Soft cheeses such as cream cheese, cottage cheese, shredded cheeses, and goat cheese must be refrigerated for safety. As a general rule, hard cheeses such as cheddar, processed cheeses (American), and both block and grated Parmesan do not require refrigeration for safety, but they will last longer if kept refrigerated.
In Europe, farms vaccinate chickens against salmonella. That means the cuticle is still intact when eggs are sold. Refrigerating eggs with the cuticle intact could actually cause mildew to grow. Which could cause… you guessed it salmonella contamination.
According to food safety experts, once you open a bottle of Worcestershire sauce, it's best to store it in the refrigerator to prevent spoilage. The cold temperature slows down the growth of bacteria and other microorganisms that can cause the sauce to spoil.
Answer: You can let an opened jar of mayonnaise sit out at room temperature for up to 8 hours, says the United States Department of Agriculture. Opened mayonnaise that has been held above 50 degrees Fahrenheit for more than 8 hours should be discarded.