The bacteria that cause foodborne illness, called pathogenic bacteria, can grow rapidly in food that’s above 40 ⁰F and can double in number in little as 20 minutes. Pathogenic bacteria doesn’t affect food’s odor, taste, or appearance, so you can’t tell it’s there. As a safety precaution, the USDA suggests not consuming meat that has been left above 40⁰F for more than two hours. This not only applies to raw food, but cooked food as well.
This is another example of where remote temperature monitoring is so important. What if your refrigerator’s not working right? Sure, it may seem like it’s okay, but maybe the temperature controller’s not working right, or maybe it’s the compressor. You may have set it to store food below 40⁰F, but maybe that’s not the actual temperature. What if we were talking about a restaurant walk-in refrigerator in the middle of the night? How would you know? Having a monitoring system that not only tells you what the actual temperature is, but also send you an alert would be crucial in a) making sure none of your restaurant patrons get sick and b) ensuring you don’t have to throw away hundreds of dollars worth of food because of poor refrigeration.
More information about proper food refrigeration can be found on the USDA’s website here and here.
The risk in this article is not a smell or a change in color. Pathogenic bacteria can grow in food that still looks, smells, and tastes normal, and the USDA’s precaution is not to eat meat that has sat above 40°F for more than two hours. That limit covers raw meat and cooked meat.
A refrigerator dial set below 40°F is not the same as food held below 40°F. The controller or the compressor can be wrong, and a walk-in can drift overnight when nobody is there to open the door. A useful check has two parts: a sensor on the temperature the food is actually sitting in, and an alert when that reading leaves the range. If the food has already been above 40°F past the two-hour mark, the precaution is to throw it out rather than serve it and hope.
The temperature range the USDA describes for this kind of growth is the danger zone of 40°F to 140°F. Cold storage is the bottom of that range. Keeping cooked food hot is the other side of the same rule, and it is a separate check from the refrigerator.
For more on temperature monitoring, read Essential Temperature Control Tips for Restaurant Food Safety and What Is Time/Temperature Control for Safety (TCS)?.