Why do some food items last for weeks and others spoil in just a few days?
Food items last for different durations depending on the conditions that favour or prevent microbial growth. Microbes need moisture, air, and the right temperature to grow.
Foods that spoil quickly, like cooked uttapam, bread, milk, and cut fruits, contain moisture and are exposed to air, allowing microbes to grow rapidly.
Foods that last for weeks or months have been preserved using methods that remove one or more conditions needed for microbial growth.
For example, pickles last long because oil keeps air away from microbes. Dried foods like chilli powder last because moisture has been removed.
Refrigerated foods last longer because cold temperature slows down microbial growth. Foods preserved with salt, sugar, or spices also last longer as these substances prevent microbial growth.
Thus, the presence or absence of moisture, air, and suitable temperature determines how long food remains unspoiled.
Explanation
The chapter explains through multiple findings that microbes need moisture, air, and the right temperature to grow (Finding #2). Finding #3 states that drying removes moisture and prevents microbial growth. Finding #4 explains that oil keeps out air and stops microbe growth. Finding #5 states that cold temperature slows down microbes. Finding #6 mentions that salt, sugar, and spices are also used to preserve food. Foods that have been preserved using these methods last longer, while foods with moisture and air exposure spoil quickly.
Solution Steps
Microbes need moisture, air, and the right temperature to grow
Foods with moisture and air exposure spoil quickly (e.g., uttapam, bread, milk, cut fruits)
Preserved foods last longer because preservation removes conditions needed for microbial growth
Oil in pickles keeps air away from microbes
Drying removes moisture to prevent microbial growth (e.g., chilli powder)
Cold temperature in refrigeration slows down microbial growth
Salt, sugar, and spices prevent microbial growth and preserve food