Science Questions

I heated up a non-vegetarian pizza the other day. The bit in the middle wasn’t very well-cooked. How dangerous would it be to eat the pizza? James, Derby

Chris: You should always make sure things are fully-cooked. The reason for doing that is that bacteria may have settled on the food when it was being prepared. They may have only been there at very low levels when the food was being prepared. If it hasn’t been stored very well, those bacteria can persist. Bacteria can easily survive the temperatures in your freezer. Bacteria can survive being frozen down to -200 degrees. If you don’t warm food thoroughly to kill the bacteria you get some bits which are just warm enough to sustain a much better environment for the bacteria so they grow really fast. When they grow very fast they can either infect you, like salmonella, or they can produce toxins into the food like staphylococcus aureus. This produces a toxin which can cause diarrhoea and vomiting. That toxin is also stable so that if you thoroughly re-heat the food, unfortunately you can still get problems because the toxin is still in the food. The moral is to make sure you cook things absolutely thoroughly.

November 2007