Cross-Contamination of Food

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson, we will learn about cross contamination, including why it is important to not use the same cutting board to cut chicken and then cut other food and why we need to frequently wash our hands while cooking.

Cross Contamination

We've all grown up hearing that we shouldn't cut our chicken and lettuce using the same cutting board. We need to wash our hands frequently, particularly when we are in contact with food, and to not mix cooked and raw foods. All of these are ways to prevent cross contamination in our own kitchens and in the food that we eat.

Cross contamination is taking microbes (or other contaminants) from one source and transferring them to another source. This can occur frequently in food preparation since some food products have a lot of microbes and humans are also a huge source of microbes. Cross contamination is important to understand both in the home and in the food industry.

Think about cross contamination like tracking dirt into a room. If you went outside, then walked inside, you could easily transfer dirt from outside to inside if you left your shoes on. If it was very muddy outside, then you will probably transfer a lot more dirt inside than if you were walking on a clean sidewalk the entire time. Many of the points that are emphasized are where it is much more likely to transfer extra 'dirt' (or microbes) from one place to another.

From Food to Food

Some products naturally have more microbes. For example, chicken will frequently have salmonella all throughout the meat. On the other hand, a potato chip probably has very few microbes in (or on) it. Think of the chicken like the muddy walk that you were trudging through while the potato chip is the clean sidewalk. When working with chicken, if you don't clean your hands and change cutting boards and other utensils, then it is very likely that you will transfer microbes from the chicken to another product. Just like after walking through mud (if you don't remove your shoes), it is very likely that you will transfer dirt from outside to the inside of the house.

Potato chips are not very hospitable for microbes. There is little to no available water for microbes in potato chips (water is necessary for microbes to survive, just like for humans). They are also very salty (high salt concentrations will kill microbes). The potato chips are like the clean sidewalk. The chances of transferring any microbes from potato chips to another food is very unlikely. It is more likely that you will transfer salt from the potato chips to another product than transferring microbes.

So we need to keep in mind food products that are likely to have microbes present. These food products must be treated with care. After handling these products we must wash our hands and any other surfaces that may have come in contact with the microbe laden food.

From Humans to Food

We don't often think about it, but we are full of microbes. Some of these microbes are actually good for us, while others may make us sick. So we need to be careful to not transfer microbes from our self to our food. This is particularly of concern if we are sick or if we have recently been sick because the number of disease causing microbes, or pathogenic microbes, is much higher in these cases.

The most common microbe to cause food borne illnesses is Norovirus. The interesting thing about this virus is that it does not grow very well outside of a human. So it needs a human host to carry it from one person to another. One common way that this occurs is through food. As we prepare food, we frequently use our hands, which (if we haven't washed them) could have Norovirus on them. Shortly after preparing the food, it can be eaten by someone else and cause them to get sick.

You may think 'but I haven't been sick recently so why do I need to worry about contaminating food?' There are several reasons. First of all, you have probably touched many things throughout the day, and you don't know what microbes were on those surfaces. Also the microbes can be in your system for weeks before and after you actually feel ill. Another reason is that your body might have been strong enough to fight off the virus but others, particularly the young and old, may not be strong enough.

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