Page 194 - Agriculture_Form_Three

Agriculture for Secondary Schools

bulgaricus and Streptococcus thermophiles) into pasteurised milk. For mala milk, the
bacteria used are mesophiles which include Streptococcus lactis and Streptococcus
cremoris, whose culture may be incubated at relatively low temperature compared
to the thermophilic types.

Requirements for making yoghurt and mala milk
(a) Fresh milk: The milk must be clean and safe, coming from healthy cows or
goats. Check the milk for colour, smell, presence of any foreign matter, density,
microbial contamination and seek to know if the cows had been treated with
antibiotics in the past 4 days.
(b) Stove: This could be powered by electricity, gas charcoal, or fuel wood
(c) Utensils: Cooking pans, buckets or any other type of pans in which milk could

be boiled for pasteurisation. This also includes fine sieve or clean cloth for
filtering the milk.
(d) Clean water: Safe clean water to be available all the time.
(e) Other requirements: Thermometer, lactometer, incubator or cool box, refrigerator
or cool storage facility (especially for yoghurt) as well as packaging material
should be made available.

Procedure of making yoghurt
Step 1: Examine the milk by checking smell, colour, cleanliness, measure density
and run all important tests mentioned earlier.

Step 2: Heat the milk to 90 - 92 C ; stir the milk all the time to avoid milk sticking at
°
the bottom of pan. Alternatively, you may heat the milk held in a container immersed
in a vessel with boiling water (a water bath). Hold the milk at 90 - 92 C for 3 - 5
°
minutes before taking it out of the heat source.

Step 3: Allow the milk to cool to 41 - 42 C . Measure out a small amount of milk
°
into a cup. Add the required amount of yoghurt culture and stir well before mixing
back with the entire batch of the milk. Stir slowly and place the incubator set at
41 - 42 C then incubate for 3 - 4 hours.
°
Step 4: After 3 - 4 hours the yoghurt should have set. Carefully place the setting
yoghurt into a refrigerator or a cool area to fully mature at 5 C . This may be overnight
°
for the flavours to fully develop. Finally, you may add flavours or sweeteners, ready
for packaging. You can choose many food flavours. Some people like to add fruits,
e.g., banana, strawberry, and also nuts, e.g., peanuts and cashew nuts.

Student’s Book Form Twos Book Form Three
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AGRICULTURE FORM 3 9.11.2022.indd 183 10/01/2025 12:31