Why does milk go off?
During our study of Ancient Egypt we carried out a scientific inquiry into how and why milk goes rancid. In Ancient Egypt milk played an important cultural role, with both a religious significance and health benefits. The last ruler of Ancient Egypt, Cleopatra, was even said to bathe in fermented milk to keep her skin young and soft! Read the below work written by a pupil:
"First we selected four different kinds of milk/substitute: Semi-skinned, UHT, Almond and Soya. We then carefully measured the same amount of each of our milks into clean containers. The we put took initial readings using universal indicator paper (litmus paper) before putting the milks in the same location to ensure a fair test."
We then tested our milks every day for the week and recorded our findings in the table below:
Using the skills we had developed in our maths lessons, we plotted our results onto a line graph. This helped use to see visually the changes in acidity. See one of our graphs below:
Using our date we were able to conclude:
"Pasteurised semi-skinned milk and HUT milk had the highest changes in acidity because they have lactose sugar in them which meant that they developed lactic acid. These milks began to clump together and for harder curds. The substitute milks that were not dairy were found to be less acidic after 5 days as they did not develop lactic acid."