Lab: Chemical Test to Show If Milk Is Off

How do we chemically show that milk is off?

Background investigation

The problem that my associate Keely and I wanted to analise was how to chemically test and show that milk is off and how this happens. We wanted to know this because we have just purchased a small dairy farm on the outskirts of Camperdown Victoria. We are curious about the science behind off milk, and are wondering if there are ways our milk stay fresher for longer.

Aim

The main focus of our experiment was to find out the difference between milk and off milk by testing its acidity an ph levels. We also wanted to know about the science behind off milk and what exactly in the milk makes it go off, how this happens and what sort of reaction this was. I predicted that the lower the Ph levels where the more off the milk would be.

Equipment * Off full cream P ura milk- had been left out in sun for a week * Fresh full cream Pura milk * Litmus paper * Beaker * Test tubes * Universal indicator

Method 1. Put off milk and fresh milk into two separate beakers 2. Pour a small sample of fresh milk into a test tube 3. Pour a small sample of off milk into a new test tube 4. Dip litmus paper into each of the test tubes and remove. 5. Check the colour of the paper and see what it has changed to. 6. Write down the ph level of both milks using the color guide given on the box of litmus paper. 7. Repeat steps 2 to 6 once more. 8. Put 3 drops of universal indicator into 2 new test tubes of fresh and off milk. 9. Record ph levels 10. Repeat steps 8 and 9 once more.

Results Title | equiptment | Acid Level | Ph levels | colour | Off milk 1 | Litmus Paper | Acidic | _ | Litmus paper turned red | Off milk 2 | Litmus Paper | Acidic | _ | Litmus paper turned red | Fresh milk 1 | Litmus Paper | Non acidic | _ | Litmus paper stayed blue | Fresh milk 2 | Litmus Paper | Non acidic | _ | Litmus paper stayed blue | Off milk 1 | Universal Indicator | acidic | Ph 4 | Pinkish | Off milk 2 | Universal Indicator | acidic | Ph 3 | Dark pink-red | Fresh milk 1 | Universal Indicator | Neutral | Ph 6 | yellow | Fresh milk 2 | Universal Indicator | Neutral | Ph 6 | yellow |
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Ph levels chart Ph3 acidic-----------------------------Ph 11 base

Discussion
My aim was to find out the difference between the ph levels and the acidity in off and fresh milk. I predicted that the off milk would have higher acidity levels and lower ph levels because a lactic acid is produced when it goes off.
The findings of my results show that I was right. As the milk went off more lactic acid was produced which made the Ph levels go down (meaning more acidic) and the acidity go up. My results show this is true because when the acidity was tested using litmus paper only the off milk made the paper change colour showing that it was acidic.
My results show that as the milk went off more acid was produced, which eventually makes the milk go off and sour.
Some errors that may have occurred was the different types of brands of milk we were using for instance the brand of milk we used may have given a different result than ones others used. We could have conducted our tests on more than one brand of milk to give us a broader idea of what is happening and if it is an accurate result.

Conclusion
I found that that my predictions where right and I now have the evidence to back it up. Off milk has higher acidity levels than fresh milk, and lower ph levels also which creates that sour taste and rotten smell you so often get in off milk. Lactic acid and bacteria is produced as the milk gets older and it cannot be stopped. This will help me and my partner run our dairy as we know that it is important to just keep our milk fresh and not leave it around in the sun. I think that this should be common knowledge to everyone who drinks and works with milk, to help keep everyone healthy. A further investigation about how off milk can be used other than being thrown away would be interesting, as it would help us get everything out of our milk. It would help us to not put anything to waste and hopefully increase the quality of our production.