Summertime means back yard bar-b-ques and long hikes to secluded picnic spots in our national forests. That means side dishes like potato and macaroni salads, prepared with mayonnaise. On my sandwiches, I prefer mayo over other condiments like mustard. Yet, I am regularly warned by concerned family members about not taking my sandwiches with mayo on hikes where there won’t be any refrigeration for a while. Or in leaving the potato salad out on the picnic table for too long allowing the mayonnaise to spoil. Are they right? If so, why haven’t I gotten sick? Here’s why.
Traditionally, mayonnaise is a blend of oil and egg yolks that is seasoned with vinegar, lemon juice, salt and sometimes mustard. The egg yolks serve as an emulsifier that stabilizes the mixture. However, mayo gets it’s bad reputation from these egg yolks which can spoil quickly especially in home made varieties that use unpasteurized eggs. Commercial brands of mayonnaise use pasteurized eggs, or substitute the egg yolks with another emulsifier that doesn’t spoil.
But aside from the fact that I’ve never attempted to make, let alone use, home made mayo, here’s why I’ve never gotten sick. The vinegar and/or the lemon juice in commercial mayonnaise creates a very acidic mixture, with a pH in the range of 3.8 – 4.6. That’s a pretty hostile environment for bacteria like salmonella and staphylococcus, the ones that cause most food poisoning.
One study at the University of Wisconsin found that mayonnaise actually reduced bacterial levels in prepared salads, thereby retarding their spoilage. What the researchers found was that the bacteria begins to grow on the other ingredients of the salad or sandwich, not in the mayo. They found that when they added the mayo, the bacterial count immediately dropped! After 24 hours, the food samples with the mayonnaise had fewer bacteria than the food without.
One of the conclusions the researchers came to was that mayonnaise should be added during the initial preparation of the salad or sandwich, rather than adding it shortly before consumption. The reason is that the other ingredients receive the protection of the mayo’s high acid content, reducing bacterial growth during the time outside of refrigeration.
Now, it’s important to add that putting mayonnaise on your food is not a substitute for proper refrigeration. The researchers also add that unrefrigerated foods should be kept out of direct sunlight and that any leftovers that have been without refrigeration for several hours should be discarded.
So, when it comes to your next picnic, there’s no need to hold the mayo – unless you love mustard.