You may have heard a sentence: "Let the food be cool before ice it in the refrigerator. You can save electricity through this!!!" Indeed, allowing food to gradually cool down by exchanging heat with room air can save some electricity, but the health risks brought by this approach may exceed your imagination!
The health risk comes from the growth of microorganisms in food. In the field of food safety, there is a term for food preservation, Danger Zone, which refers tothe temperature range of 4 degrees to 60 degrees Celsius (40 degrees to 140 degrees Fahrenheit), In this temperature range, common pathogens (such as: Staphylococcus aureus, Salmonella enteritidis, Escherichia coli O157:H7, Campylobacter) will multiply at a very fast rate. they may even double the amount every 20 minutes. As the temperature rises, the pattern of growth rate of microorganisms will be close toExponential rise. Then, the risk of food poisoning rises accordingly.
Generally speaking, we often use 10^5 CFU/g (the total number of bacterial colonies contained in each gram of sample is 10^5) as the boundary of bacterial pathogenicity. If we further analyze the causes of bacterial growth, there are two major factors: (1) the initial amount of bacteria and (2) the growth rate of bacteria. Based on the above factors, we can find better food handling and preservation methods.
[Factors affecting food-borne bacteria and Improvement methods]
Initial bacterial load
This refers to the bacteria contained in the food at the beginning. It may be originally stored in the food itself, or it may come from the pollution of the external environment. Basically, as long as there are enough time and temperature for food heating, the bacteria contained in the food can be almost totally killed. But the recommended heating temperature and time vary, depending on the type of food. Generally, it is recommended thatthe heating temperature should not be lower than 60 degrees Celsius. That is why, in the buffet restaurant, there is always a heater below the foods, so as to keep the bactericidal effect and preserve the foods for a longer time. The recommended heating temperatures for different foods are showed in the following figure:
As for external environmental pollution, it is generally related to environmental cleanliness and hygienic habits. If food is cooked or placed in a messy place, and personnel have poor hygiene habits, a large number of pathogenic bacteria may fall into the food through dust and dirt. Therefore, it is very important to cover food containers to isolate the food from the external contamination.
Bacterial growth rate
There are many environmental factors that affect the growth rate of bacteria (such as: pH, water activity, temperature, humidity, etc.). Here, we will only discuss the effect of temperature. Basically,the higher the temperature, the growth rate of bacteria will increase almost exponentially, So it is recommendedDO NOT leave food in the Danger Zone (4°C~60°C) environment for too long. Generally speaking, DO NOT keep food outside for more than 2 hours. Leftovers should be put in the refrigerator as soon as possible.To speed up the cooling rate, you can consider putting food in a shallow container, to increase the speed of heat exchange with the air. However, please pay attention to whether the surrounding environment is clean or not. Otherwise, it is better to put the covered food container directly into the refrigerator, to prevent it from environmental contamination.
In addition,the summer temperature in Taiwan is generally very high. We suggest that the food/leftovers should be placed in the refrigerator as soon as possible, instead of leaving them in a high temperature environment for too long, to reduce the risk of food poisoning.
【Tips for Food Preservation】
1. The food container should be covered to isolate it from the external contamination.
2. DO NOT leave the food at room temperature for more than 2 hours.
3. If the room temperature is too high, DO NOT try to let the food cool down and just put the food in the refrigerator directly with cover.
Mydocsay.com