How I make traditional homemade yogurt
I have 2 litres, whole, pasteurized, homogenized, cow’s milk, 5-7 days lifespan, and I want to manufacture yoghurt.
To manufacture yoghurt, I have to coagulate the milk.
In yogurt manufacture, the coagulation of milk is achieved through acidification.
The concept of yoghurt is determined by the lactic fermentation, by the action of specific microorganisms, and thus requires the existence, i.e., the addition of a particular lactic acid bacteria culture.
It is yoghurt yeast, yoghurt culture.
It consists of two genera of bacteria, which act and grow in synergy.
They are Streptococcus thermophilus (Str) and Lactobacillus bulgaricus (Lb).
These two bacteria in milk, they will take up lactose.
They use glucose to meet their energy needs and eventually convert it to about 95% in lactic acid.
This lactic acid causes the acidification of the milk, the drop in its pH value and finally the milk coagulation.
Where will we find them?
And how do we add them?
There are here, if we have got a clay pot packaging.
When it comes to plastic cups packaging, it is sufficient to be indicated
that it contains yoghurt yeast or yoghurt culture.
So, what we need to do is take a quantity of these yoghurts, a small one because we expect the microorganisms to multiply.
And accordingly, we will add this quantity to our milk.
Both my microorganisms are thermophilic.
That means, they like heat.
Str has an optimum temperature, ideal temperature, at 40°C, and Lb at 45°C.
It is very important, therefore, at what temperature and for how long time I heat my milk.
There are 3 trends.
The 1st trend is to heat at 85°C for 30 minutes.
The 2nd trend is to heat at 90-95°C for 5 to 10 minutes.
And the third trend is to heat at a temperature close to 100°C for 20 seconds to 1.5 minutes.
We, here, are going to heat at a temperature of 92-93°C for 6 to 8 minutes.
Generally, I do not recommend heating the milk above 95°C.
By this heat treatment, I will achieve the greatest water retention capacity, the lower syneresis, the higher viscosity, without having a significant effect on the organoleptic characteristics of the milk.
We are at 92 to 93°C.
We are stirring continuously for 6 to 8 minutes.
The time is over.
I stop heating.
I will transfer the hot milk to the calibrated container.
Initially, I had a volume of 2l of milk.
We can see that the volume has been reduced to 1.7l or 1700ml, after the heat treatment.
That is, we had a water evaporation of about 300ml.
So, I should cool my milk down up to about 50°C so as to get enough time to prepare yoghurt culture.I will add an amount of yoghurt culture between 2 and 3% v/v.
I will choose an average value of about 2.5% v/v, so, 2.5 to 3% v/v of the 1700ml is about 50 ml.
Yogurt culture inoculation
Or roughly we can say 50g of yoghurt culture.
Do not transfer all quantity directly into the milk.
Firstly, you should dissolve the yoghurt culture.
Or you should use a matching filter such as a drainer.
The second time we can use a filter or a drainer with smaller holes.
As a result, dissolution is even more effective.
I transfer the milk into small bowls.
I will use the oven as an incubation chamber.
I’ll put my thermometer inside the oven so as I can measure, control and change the temperature at will.
Usually, when the ratio of Str to Lb is 1:1, when the quantity of yoghurt is 2.5% and when the incubation temperature is 42-43°C, it will take 3 to 3.5 hours to complete the whole process.
After 3 hours and 15 minutes, the pH value is 4.50.
I could say, that the process has essentially completed.
So, we will take our samples out of the oven.
We will let them get a room temperature of 20-25°C and then we will place them in a refrigerator.
There the yogurt can be stored for at least 15, 20 days