Fermentation is the conversion of a carbohydrate
such as sugar into an acid or alcohol.
Fermentation can be performed by yeast and
some types of bacteria.
Milk is contaminated by bacteria even before it
leaves the udder, although at this point they are
harmless and few in numbers.
The two main groups of bacteria in milk are Lactic
acids and coliforms. Lactic acid is the normal
bacteria present in milk and dairy products.
Coliforms are the main reason for milk spoilage.
Before After 1 day
A glass of fresh milk was left for one day. It smells
sour and even foul after that. What happen to the
Planning and Doing Experiment – observation of the
change in pH when the milk is left for 1 day.
1. Observe and explain the change of pH
after starting the experiment from the
2. What causes the reduction in the pH of
3. Describe the speed of change in pH the
whole experiment period?
4. Calculate the extent of change in pH
obtained in the process.
School Milk Program has to be postponed for a time being
because the food poisoning case among students due to milk
spoilage. Based on your opinion, what are the factors that cause
the milk spoilage?
By using data
logger, we do not
need to make a
The slightly changes
in the pH values are
able to be observed.
We do not need to
use pH test papers
during the whole
Measuring the pH of Milk. Retrieved
on 31st August 2010 from