Sunday, August 5, 2007


Does mayonnaise need refrigerating?

We all know that at picnics, we have to be especially careful of mayonnaise-based salads. The potato salad, macaroni salad, and coleslaw. That mayo will spoil in the hot sun! Keep it covered. Put it out at the last minute and throw it out once everyone is served. It's like a biological time bomb. The salad that could kill us all!

When, all of it. Every word of it. Is FALSE. You're more likely to get food poisoning from contaminated meat or veggies in those salads than the mayo.

First, what is in mayonnaise? Oil. Vinegar. Lemon juice. Raw eggs. Salt. Spices. As we can see, most of this stuff won't really spoil. Everything but the raw eggs. Ah! But, in commercial mayo, the eggs are first pasteurized so they are CLEAN. Then we have the vinegar and lemon juice. Mayo is actually pretty acidic.

From Hellman's website, they state it should be refrigerated as higher temperatures will affect flavor. No mention of spoilage. But, to really get the facts, we go to the Association for Dressings and Sauces. Yes, it exists. They state mayo gets a bad rap. Most likely because homemade mayo is made with regular raw eggs which makes them very perishable. But, as stated, commercial mayo uses pasteurized eggs. The issue is cross contamination of other ingredients. Mayo isn't strong enough to kill new bacteria introduced into the salad. So, that pasta salad without mayo will go bad if you have other bad ingredients.

Other testimonies from the web state many people never refrigerate their mayo. NEVER. And, as Hellman's says, they're only concerned about loss of flavor. So, similar to ketchup, you can keep mayo in the pantry as long as you use it enough so that the flavor doesn't go south. Who knows how long that is. But, you won't get sick.

Saturday, August 4, 2007


Does ketchup need refrigerating?

Perhaps the first thing that got me to think of this topic. Of course you put ketchup in the refrigerator. Everyone does. Yet, we use plenty of unrefrigerated ketchup at diners, restaurants, and ball games. You know it's just sitting there for hours, maybe days on end. Wouldn't it go bad? Maybe these places use it so fast that it can't go bad. Or maybe not.

Well, first, what is ketchup? Tomatoes of course. Spices. Vinegar. Salt. Sugar. Well, vinegar and salt (less so sugar) can prevent spoilage. Ketchup is actually very acidic and salty. Heinz "suggests" refrigeration on their website to help prevent spoilage. But, no "thou shall" wording. There's not a mention of it on Hunt's website. Checking the web, many people state ketchup does not require refrigeration. Some state their ketchup bottle has no warning whatsoever. Here's what I can discern.

Ketchup does not spoil quickly. Weeks, maybe months should be fine on a shelf. But not forever. But nowhere is it written how long it will last. There is no mention anywhere of the flavor changing until it spoils. Many prefer it warm over cold.

Here is the fine print. If you use a lot of ketchup, then the shelf is probably fine. But, this assumes you keep it out of sunlight and at room temperature. General food safety rules apply. Don't touch the lip. Don't cross contaminate it with food or wiping the lip with a rag. Don't refill it. And be on the look out for spoilage or mold growth. But, if you use a bottle every 18 months, keep it in the fridge and check it for spoilage.

Another caveat. There are many lower sodium, no sodium, and organic varieties. These might not be as safe on the shelf.

Friday, August 3, 2007

The Weapons

Vinegar. It is a powerful antibacterial. It is a low pH acid. Most bacteria do not survive in that environment. Can be seen as an ingredient to its use in pickling. Even more potent when combined with salt.

Acid. Includes vinegar, citric acid, and others.

Salt. It absorbs the water in and on the food. Without water, bacteria cannot live or multiply. In high concentrations, it can also pull the salt right out of the cells of the bacteria and killing it.

Sugar. It absorbs water similar to salt. The concentration must be very high to be effective. Mostly can be seen in candies that have an extremely long shelf life.

Heat. It kills. Used to sterilize containers, kill bacteria in food in the containers, and pasteurization.

Freezing. Freezing temperatures either kill the bacteria or put them into "hibernation". Most foods will last forever in the freezer if it weren't for freezer burn.

Smoke. I have no idea how but smoke kills bacteria as well. Seen in smoked meats.

Dehydration. Removing almost all the water in the food will prevent bacteria from growing. Used in jerky and other cured meats.

What is Spoilage?

What exactly is spoilage and what causes it? There are probably textbooks written about this. So, this will be just a high level overview. One way for things to spoil is through growth of bacteria. Over time, foods will breed bacteria. They will use the water in the food to drink, and proteins and sugars from the food to eat. This will eventually lead to the food breaking down into goo. It will smell bad from all the gaseous waste from the bacteria. Eating this food will lead to sickness and perhaps death due to the bacteria invasion. Some nasty bacteria include botulism and e-coli. Some of the bacteria is just from the environment. Others will be through cross contamination from your hands or counter top. Finally, there is bacteria already present within the food at extremely low levels that then multiply to toxic levels.

Another way for foods to spoil is through mold and yeast. Airborne molds and yeast which are present EVERYWHERE. They attach to the food and eat and drink just like bacteria. Most of the time, eating moldy/yeasty food will not be very healthy. Of course there are exceptions like blue cheese and penicillins. Other times the exposed area can be cut off since these generally don't penetrate very far into the food. But, that should be left for the experts!

These spoilers require a certain environment to grow. They need food, water, air, and sometimes light. They also operate in certain temperature ranges. So, taking away some or all of these things can slow or prevent spoilage.

That's what it means when foods go bad or spoil. It's the bacteria, mold, yeast, and other nasty things that will make you sick or kill you. So, it's pretty obvious why we don't want to eat spoiled food! In order to understand what the fridge does, we need to understand what it's trying to prevent.

The Answers

Given it is impossible to tell from the packaging what needs to be refrigerated AND why, this blog comes into existence. For whatever reason, I've always pondered these questions. Perhaps partly because I like food, a part of the scientist in me, and an over crowded fridge, I've decided to blog about it. I want to go through a vast array of foods and determine what, why, and for how long. I will use information from government websites, product sites, encyclopedias, and anywhere else I can find. When possible I will cite my sources. I will also try to debunk certain myths. Most importantly, I will educate myself and whoever in this world has similar questions. Let's get started.

Two Reasons

There are two main reasons to refrigerate something. To prolong freshness and to prolong flavor.

Nothing can prevent something from spoiling that can spoil. So, the most the refrigerator can do is slow down the process of spoilage so the product lasts much longer. A steak will go bad in hours on a counter top. But will last for days in a refrigerator. This is what we typically think about what a refrigerator does and why we put stuff in it. But that's only one reason.

Another reason is to prolong flavor. Besides by spoiling, some foods just lose their flavor if left out in the open. The refrigerator slows this flavor loss. It can prolong flavor by months or years.

Some foods that never spoil will lose their flavor. This is the surprising part. Many foods will last forever in an open container on the shelf in your pantry. They would just taste horrible over time. In fact, many of the "Refrigerate After Opening" warnings are for flavor reasons only.

The Question

It starts innocently enough. You crack open a jar of something from the pantry. You use a bit of it. You go to put it back on the shelf when you ask, "Should I put this in the refrigerator?" You do the bottle roll in your hand to see those prophetic words "Refrigerate After Opening". You look on the label. Then the cap. The the bottom. It doesn't say it. So you put it back on the shelf. But, in the back of your mind you're wondering, "Why wouldn't it need refrigerating? What if I missed it? What if they're wrong?!" So, you go grab it and put it in the fridge.

After a while you may have the opposite question. Why does this need refrigerating? Nothing in the universe can live in a bottle of soy sauce due to the salt. So, why does it tell you to refrigerate it? It can't possibly go bad! You've kept it on your pantry shelf for years and never gotten sick. Are you just lucky?