Is mayonnaise-containing food okay to eat after being left out? My father-in-law says yes but the rest of the us can’t seem to agree.

The debate over whether mayonnaise-containing foods are safe to eat after being left out at room temperature is a common one, often causing disagreements in families and among food lovers. Mayonnaise, a staple in many kitchens, is frequently misunderstood—some people believe it's a high-risk food, while others, like your father-in-law, might not think twice about eating a sandwich that's been out for a while.

But what does food safety science have to say about this contentious issue? Let's dive into the facts to resolve the dilemma and shed light on the best practices for handling mayonnaise-containing foods.

Mayonnaise is an emulsion of oil, egg yolk, and an acid—either vinegar or lemon juice. The commercial varieties often contain additional ingredients like preservatives that help to inhibit bacterial growth, making them more stable than homemade versions. It's essential to understand why there is a concern about mayonnaise and related food items:

1. Mayonnaise contains eggs, which are a potential source of the bacteria Salmonella. If the eggs aren't pasteurized or the mayonnaise isn't handled correctly, there's a risk of foodborne illness.

2. At room temperature, bacteria that can cause food poisoning, such as Staphylococcus aureus and Bacillus cereus, can grow rapidly.

3. Mayonnaise itself can act as a barrier to bacteria, but once it's mixed with other ingredients like chicken, potatoes, or pasta, the combination can provide a better environment for bacteria to flourish if not kept cold.

The U.S. Department of Agriculture (USDA) offers specific guidelines when it comes to perishable foods like those containing mayonnaise:

1. Perishable foods should not be left out of the refrigerator for more than two hours. If the ambient temperature is above 90°F (32°C), this window is reduced to just one hour.

2. Bacteria grow most rapidly in the range of temperatures between 40°F (4°C) and 140°F (60°C), which is known as the "danger zone." Keeping foods out of this temperature range helps to minimize the risk of bacterial growth.

3. If food has been left out for longer than recommended, the safest option is to discard it to avoid the risk of foodborne illness.

In order to enjoy mayonnaise-containing dishes safely, consider the following practical tips:

1. Always refrigerate mayonnaise and mayonnaise-based foods promptly after serving.

2. When bringing dishes to outdoor events like picnics or BBQs, keep them in coolers with ice packs to maintain a safe temperature.

3. If you're uncertain about how long food has been left out, it's best to err on the side of caution and not consume it.

4. Use separate utensils for mayonnaise-containing dishes to prevent cross-contamination with raw foods, particularly meat.

While your father-in-law might have been lucky so far with his practice of eating mayonnaise-containing foods left out for undefined periods, the scientific consensus is clear. To prevent foodborne illnesses and ensure the well-being of everyone, it's crucial to adhere to food safety guidelines that caution against consuming such foods if they've been at room temperature beyond the recommended limits. It's not just about preference or individual constitution—it's about minimizing risk and practicing good food safety habits for the health of all. When in doubt, throw it out.