MSU Extension

There it is, sitting at the back of the fridge. You vaguely remember putting something in that particular leftover container about a week ago, but you can’t remember what it was. Is it still good? How do you know? Is it worth the risk? I was recently listening to a popular food safety podcast and the issue of food spoilage vs. food pathogens comes up over and over as one of the top misunderstood aspects of food safety. With food product date labeling confusion, and a general little common knowledge about food-borne pathogens, it’s no wonder that sad little container of leftovers continually gets shoved to the back of the fridge. The first thing to do is learn the difference between food spoilage organisms, and food pathogens that cause food-borne illness. 

Let’s start with food spoilage organisms. These can be yeasts, molds, fungi, or bacteria that will eventually grow on any food as the same food that feeds us also provides nutrients that these organisms can live on and grow in. These organisms are often smelled, seen, or tasted such as; the smell of spoiled milk, that blue fuzzy stuff growing in your leftovers, or bread that tastes like “dirt,” which is actually mold that you just haven’t seen yet. Foods that are spoiled often have a different color than when they were fresh, feel slimy, or smell rotten or sulphury. The good news is, that for the most part (there are always exceptions), food that is spoiled won’t make you sick. Although some people may become physically ill due to smells or disgusting flavors, food spoilage organisms don’t cause life-threatening infections. 

Food pathogens will, however, make you sick, possibly even cause death. A pathogen is a biological agent that causes disease or illness to its host. When it comes to food, these include bacteria, viruses, and parasites. Examples that are commonly known are E. coli, noro virus, and giardia, but there are about 200 known food-borne pathogens in the world. Unfortunately these organisms cannot be seen, smelled, or tasted, and it often takes very few of them to infect a person. 

This is where things start to get tricky. How do you know, then, if your food has pathogens on/in it? You don’t, but if food is handled properly you can reduce the chances of pathogens being present. A general rule of thumb is if your food smells bad, tastes bad (spit it out), or feels different than it should (slimy, fuzzy, etc) then your food is under attack from spoilage organisms, and while consuming it won’t send you to the hospital, it may be quite disgusting. When it comes to leftovers, for best quality they should be consumed within a week of being cooked originally. 

The best way to prevent food-borne illness from pathogens is to follow basic food safety prectices- cook food to proper internal temperatures, avoid cross-contamination, and practice good personal hygiene, just to mention a few. Most of our food today comes in hermetically-sealed packages (milk cartons, canned goods, etc), which means both the food and the container have been sterilized to a temperature that kills pathogens that grow in food. Unless the food has been mistreated, via cross contamination or other modes, there shouldn’t be any pathogens in the food, except when there are food recalls. This is not always the case with items like fresh fruit and vegetables or meat, which are not usually processed before you buy them. Fruits and vegetables should be washed before eating, and meat should be thoroughly cooked before consumption. 

One particular food seems to cause more confusion than any other- shell eggs. Determining the freshness of eggs is challenging, in part again due to labeling issues. Technically, expiration dates on eggs are not Federally required either, so you may find cartons with no date at all. There is a method out there called the “egg float test” that many have been using to determine how old/fresh an egg is. Sadly, it is not a recommened method to decide whether or not to eat an egg. If an egg is spoiled it will smell bad, like Sulphur, when you crack it. This does not mean it has pathogens, it is just rotten and undesirable as food. All eggs can potentially have pathogens, and should be cooked to the proper internal temperature. For best quality, eggs should be consumed within 3-5 weeks after purchase. 

For more information about food spoilage or food pathogens contact your local Michigan State University Extension office, or visit us online.