Milk Experiment

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Author: Sofia PC

Grade Level: 6th - 9th;  Type: Microbiology


In this milk experiment, we will find out whether whole milk spoils at the same rate as two percent and skim milk.


When something is spoiled, it is definitely expired; but if something is expired, it doesn't have to be spoiled. Why is that? That's because the expiration date printed on the foods we eat are not always 100 percent set in stone. You should still rely on your senses and good judgment to determine whether something is safe to eat or not.

But when something is spoiled, you can most likely see or at least smell it before finding out the hard way (a.k.a. eating/drinking it and then hugging the toilet for the next few hours). Once something is consumed it is much harder to relieve than a brief nasty scent or an unpleasant sight. Never eat or drink spoiled foods; look and smell it before taking the leap and eating it!

Research Questions

  • What happens when food is spoiled?


  • Whole vitamin D milk (the milk should have identical expiration dates)
  • 2% milk
  • Skim milk
  • 3 drinking glasses
  • Magnifying glass

Terms to Know

  • Bacteria
  • Germs
  • Food spoilage
  • Milk content

Experimental Procedure:

  1. Pour the whole milk, 2% milk, and skim milk in 3 separate glasses. Label each one so you will know what kind of milk in in each.
  2. Set these glasses in the open air at room temperature.
  3. Observe what happens daily.
  4. In about three days, you should notice an unpleasant smell. Observe which glass the smell is coming from.
  5. Pour out the milk.

Suggested Chart


Day 1
Day 2
Day 3
Day 4
Day 5
Whole Milk






2% Milk






Skim Milk







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