Is It Safe To Microwave Mayonnaise On A Sandwich?

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Some days you just want hot food. A warm sandwich on a cold and rubbish day can be a real mood booster. And isn’t it better when that sandwich has the perfect mixture of creaminess and sharpness, improved with a thick layer of mayonnaise?

Now you have a choice – either a long and frustrating process of heating the oven and oiling a pan. Or you can stick your sandwich in the microwave for a few moments and minimize fuss.

One negates the comforting properties of a warm sandwich by adding clean up. The other takes no time at all. Only, haven’t you heard mayonnaise shouldn’t go in the microwave?

Food myths are abundant and confusing. It’s hard to remember whether microwaving mayonnaise was discouraged by a fear-mongering spam ad or by actual professionals.

It’s something to do with the eggs, right? Because of the yolks or the cooking process, maybe? You’re not sure of the details, but it’s definitely playing on your mind.

Don’t let it worry you anymore. Mayonnaise is perfectly safe to microwave. It is prone to splitting, so be careful not to get it too hot because of the high oil content. Prevent this by microwaving in short intervals, and removing when it gets warm.

If you’re still worrying about the eggs, then read on to understand why they aren’t as scary as they seem. You can feel safer the next time you want to microwave a sandwich by understanding what goes on behind it.

All about mayo

You’ve probably eaten mayo at some time or another. Even if you’re not a fan of it on its own, mayo is an essential ingredient to many dips and sauces.

Mayonnaise has had some bad press lately, with some arguing its more popular than it should be, especially with such a great range of other condiments lying in wait.

And as we’ve discovered more and more uses for mayo (did you know mayonnaise can be used in a cake? And hair products?) some people will be feeling a bit sick of it.

But the reason for its popularity is that it’s just so good on so many things. Sandwiches are immediately improved with a light spread of mayo. Many restaurants and cafés will use even a small dollop of mayo in their burgers and sandwiches to add to the creaminess and rounded flavor.

If you’re a mayo fan, then you’ll already know that mayo can be eaten with just about anything. From salads to Quiché, mayonnaise has become indispensable.

At the heart of it, mayonnaise is egg and oil, with a dash of acid. Not a very big deal, right? Only the sticking point for many people is the small detail that those eggs need to be raw. That’s right, mayo is made of raw egg yolks, and they don’t get cooked in the process. 

There are lots of scary warnings out there about the dangers of raw eggs. At the heart of this is salmonella. Salmonella is an infection caused by bacteria.

Most often, it’s caused by ingesting raw meats or contaminated water. In most cases salmonella causes sickness and clears up by itself. In the worst cases, salmonella will need to be treated with a course of antibiotics. 

Salmonella is nasty, and everyone wants to avoid it. Although many of us will shake it off eventually, in immunocompromised people it can be incredibly dangerous. This is one of the reasons why it’s so important to cook meat properly – heat kills the salmonella bacteria.

So can we safely microwave mayonnaise, even if it’s made with raw eggs? 

How to make your own mayonnaise

To understand the raw eggs in mayonnaise it helps to get a better idea of what mayonnaise is.

Mayonnaise is such a great base ingredient that different versions of it have started popping up everywhere. There’s garlic mayo, Sriracha mayo, mustard mayo, vegan mayo, truffle mayo, chipotle mayo, even wasabi mayo.

If you’ve yet to find a mayo out there that appeals to you, keep searching. They’re bound to create something that works any day now.

We most commonly associate mayonnaise with big tubs in supermarkets. Homemade mayo is not very difficult or mysterious, and it adds another layer of yummy.

While store bought mayo makes a good backseat for additional ingredients, homemade mayo is the star of the show. It can be time-consuming, but worth it if you’re a mayo fan or looking to impress.

The basic ingredients of mayo are things any home cook will have on hand: egg yolks, oil, lemon juice, and vinegar. Mustard and salt are also common additions.

To make your own, start by whisking 2 egg yolks well in a bowl (some recipes will call for the whole egg as a time saver, but just yolk is traditional.) If using, add 1 heaped teaspoon of mustard and whisk in to the egg.

Now comes the time-consuming part. Slowly, slowly, add 2 cups of a neutral oil, such as sunflower oil or canola oil, whisking continuously. It’s important to start by adding only a small amount of oil at a time and gradually building up. Adding too much at once will cause the mixture to split and curdle.

When you’ve added all your oil, and you have a nice, thick, mixture, add a teaspoon of white wine vinegar and a squeeze of lemon juice. Give it a final whisk to distribute the ingredients evenly, then add to a sterilized container and keep ready-to-eat in the fridge.

Those raw eggs don’t seem so scary now.

Is it safe to microwave mayonnaise?

So we’ve established that mayo doesn’t have quite such a scary ingredient list as it first seemed. But we’ve all spent years being warned of the dangers of raw eggs and the risks of underheating.

Microwaving mayonnaise is not dangerous. It might split, and you have to be careful not to overheat the oil. But it is safe to do.

It’s not the mayonnaise or the heat that causes salmonella, it’s the bacteria. If you treat your mayonnaise with care then you shouldn’t need to worry about bacteria growth. Keep the mayonnaise in the fridge when it’s not being used and don’t keep it past its expiration date. 

If you’re making your own mayonnaise, always use pasteurized eggs. These should be easy to come by in any supermarket refrigerator.

The main reason to avoid microwaving mayonnaise is simply that it doesn’t heat very well. Heated too quickly, the oil separates out and can become very hot and bubbling.

To microwave mayonnaise, do so in small increments and check on it after each turn of around 15 seconds. 

Is it safe to microwave mayonnaise in a sandwich?

Sometimes you just want a hot sandwich. They’re warming, and they’re comforting, and delicious. 

If you’ve made up your sandwich, and now you want to try heating it up, you might be worrying about the mayonnaise. Don’t be. You can safely microwave mayonnaise in a sandwich. Why is that?

For a start, you’ve probably used store bought mayonnaise. Store bought mayonnaise is safer, as it will have gone through a more rigorous pasteurization process than you can do at home.

Store bought mayo is better to use on a sandwich because it becomes a background ingredient. If you’ve gone to the trouble of making your own mayo, then you want it to be the star of the show.

Secondly, you took care when making your sandwich. You kept the important ingredients, including the mayo, in the fridge at a temperature below 40F. This prevents bacteria growth.

When you prepared your sandwich, you used a clean work surface and clean utensils. You made your sandwich right before eating, and it hasn’t been left to sit at room temperature.

And finally, the ingredients in mayo are designed to prevent the risk of bacteria growth in raw eggs. The eggs are pasteurized, and the introduction of acids like vinegar and lemon juice limit the spread of bacteria.

Why you shouldn’t worry about microwaving mayonnaise on a sandwich:

  1. The eggs in the mayonnaise are pasteurized.
  2. The acidic ingredients in the mayonnaise are limiting any bacteria growth.
  3. The mayonnaise is store bought, and treated to a higher degree than is possible for a home cook.
  4. You took care when making the sandwich, by keeping the work surface clean and using refrigerated ingredients.

The biggest takeaway should be that you should treat mayo as you would anything else in the kitchen – by being careful. Use the refrigerator, keep everything clean, and choose ingredients carefully.

More care should be taken with the mayonnaise before microwaving than worrying about the effects of the microwave. 

Why you shouldn’t be scared of raw eggs

The big, scary ingredient of mayonnaise is raw eggs. They have that reputation for a reason, but it’s an old reason. Raw eggs were the leading cause of salmonella in the United States…in the 1990s.

The processing of raw eggs has improved greatly since then, including the oh-so important pasteurization step. Pasteurization is when eggs are heat treated within their shells in a process that involves carefully timed water baths. This kills the bacteria while not cooking the eggs. Pasteurized eggs should be clearly marked.

While salmonella remains a risk in raw eggs, the risk is very small. Outside of mayonnaise, you’re unlikely to come across a reason for eating raw eggs. Mostly because they don’t taste anywhere near as nice, and they aren’t any healthier.

You might have been told to crack a raw egg into your protein powder to build muscle, but it’s not really worth it. Cooking the eggs doesn’t take much longer, and it vastly improves the taste. 

Also, raw eggs won’t cure your hangovers either. Sorry about that.

Despite the pasteurization, some people should continue to avoid raw eggs. This list includes anyone with a compromised immune system, including small children, the elderly, and pregnant women. This is a precaution, and if you don’t fall into these categories then it shouldn’t worry you.

Does mayonnaise go bad?

Store bought mayonnaise has a long shelf life when refrigerated. It lasts for up to 2 months when stored properly.

Homemade mayonnaise has a much shorter shelf life. Refrigerated, it will only last for about 1 week. 

Left out of the fridge, mayo can go off quite quickly – and bad mayo is completely inedible.

Does mayonnaise go bad on a sandwich?

Outside the fridge, mayonnaise goes off quickly. That includes when it’s on a sandwich.

So if you’ve made yourself a sandwich with mayonnaise, it’s important to keep it in the fridge. The addition of outside ingredients increases the potential for bacteria growth.

Once you’ve made your sandwich, either eat it straight away or put it back safe in the fridge. Don’t leave it out on the side.

If you’ve microwaved your sandwich, then it should be eaten straight away. 

Why add lemon and vinegar to mayonnaise? 

The importance of adding acid to mayonnaise is for the emulsification. Emulsification is when unmixable ingredients become mixable. In mayonnaise, the egg yolks, oil, and vinegar all work together to ensure the mixture doesn’t separate out.

You might think it’s odd to throw in a splash of vinegar – it’s not really enough to make any major changes to the taste. Without it, however, your mayonnaise just wouldn’t work properly. 

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Cassie brings decades of experience to the Kitchen Community.
She is a noted chef and avid gardener. Her new book "Healthy Eating Through the Garden" will be released shortly. When not writing or speaking about food and gardens Cassie can be found puttering around farmer's markets and greenhouses looking for the next great idea.
Cassie Marshall
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