Page 178 - Agriculture_Form_3

Agriculture for Secondary Schools

Lactometer test: Lactometer is a testing equipment used to measure the density
of the milk when brought to the collection centre. The reading is compared
with normal values to see if the milk is pure. The density of milk depends on its
contents and temperature. Good milk should have a density of between 1.026 and
1.035 g/ml when tested at 20 °C. If water is added to milk, the lactometer will
FOR ONLINE READING ONLY
show a lower reading. If substances like sugar, salt, or wheat flour are added, the
readings will be higher than normal. Milk that does not fall within the normal
range should be rejected.
Clot-on-Boiling (CoB) test: This is done by taking a small amount of milk sample
in a container or a spoon and holding it over a flame. If the milk coagulates on
heating, that milk should be considered to be undergoing spoilage and therefore
should not be accepted for processing or mixing with clean milk.

Alcohol test: A small amount of milk is mixed with alcohol in a test tube. The
tube is then shaken well. If the milk is spoiled or starting to spoil, it will form
lumps or curdle.

Methylene blue and Resazurin test: These tests help show the level of bacteria
in milk. The quality of the milk is judged by noting the degree of colour change.
A few drops of the test solution are added to the milk sample. If the milk is very
fresh, it stays blue. If there are many bacteria, the blue colour changes to pink.
This colour change usually happens within 30 minutes to 2 hours, depending on
how many bacteria are present. Because the test takes time, it is mostly used in
laboratories or milk processing centres.

Activity 9.9

Visit the school farm or a nearby farm and collect samples of different milk
products; then, perform the following tasks:

1. Observe the colour and smell of the milk sample. Record your observation
and decide whether the milk appears/smells normal or not.
2. Check the cleanliness of the milk by examining it visually for any dirt, dung,
hair, or visible particles. Record your findings.

3. Perform a lactometer test (if available). Measure the density of the milk at
room temperature and compare your reading to the normal range (1.026 -
1.035 g/ml). Record whether the milk falls within or outside the acceptable
range.

Student’s Book Form Three 169

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AGRICULTURE F3.indd 169