Yoghurt is a healthy source of protein, calcium, magnesium and other essential nutrients. The active bacteria in yoghurt support the intestinal flora and ensure healthy digestion. Much cheaper than supermarket yoghurt is homemade yoghurt, which also allows you to add the desired amount of sugar and fruit and, if you eat it quickly, does not need any preservatives.

 

You don't even need a special yoghurt maker to make plain yoghurt at home.
You need two litres of milk, 2 to 3 tablespoons of natural yoghurt (for the yoghurt cultures), a large stockpot that holds about 8 litres, a saucepan with a lid that holds about 5 litres, a metal or plastic spoon and a baking thermometer. The smaller pot must fit into the large pot to create a water bath.

Two litres of milk make about 2 litres of yoghurt. Fresh whole milk, semi-skimmed or skimmed milk should be used. For the first yoghurt you need ready-made natural yoghurt for the development of the yoghurt bacteria, later you can use the homemade yoghurt for the next batch.

Firstly, the water bath is made. Although it is not absolutely necessary, it prevents the milk from burning. The smaller pot is placed in the larger one and the space between is filled about halfway with water. When filling, the small pot must be held firmly so that it does not float up.

Milk and yoghurt should be used at room temperature. Thermometers and spoons should be sterilised in hot water before use.

Now pour the milk into the smaller pot and attach the thermometer to the rim.
The correct temperature for preparing the milk proteins for the yoghurt cultures is 85 degrees. This is the temperature at which the hot milk starts to foam. The water in the water bath should boil and the milk should be stirred frequently. The milk must be kept at 85 degrees for half an hour so that it thickens. In the meantime, fill the sink a quarter full with ice-cold water. It is best to add a few ice cubes.

The pot with the hot milk is placed there after the cooking time so that the milk cools down to 45 degrees. This is the temperature at which the yoghurt cultures begin to utilise the lactose in the milk and reproduce.
Now stir two to three tablespoons of the finished yoghurt into the milk. The yoghurt must now be kept warm for a while. It is best to cover the pan and place it on a very low heat on the hob. The temperature should be kept at around 45 degrees. The yoghurt must now rest here for seven hours. Then stir the thickened substance thoroughly. The yoghurt can now be transferred to smaller containers and stored in the fridge. The vigorous stirring and subsequent cooling ensures that the yoghurt bacteria stop producing lactose acid.

Leave the yoghurt in the fridge overnight. The next morning it is ready to eat and should have stiffened. Refrigerated and covered, the yoghurt will keep for 10 to 14 days.
The finished portions can be served with sugar, honey, jam and/or fruit. You should set aside three tablespoons to make your next yoghurt.

Summary

Sterilise spoons and thermometers
Boil the milk in a bain-marie at 85 degrees for half an hour
Cool to 45 degrees in ice water
Stir in the yoghurt
Keep warm for seven hours
Fill and chill in the fridge

The reason for sterilising the cutlery is to avoid contamination by other bacteria and to prepare the milk for the production of bacteria. The rapid heating and cooling promotes a good result.
Yoghurt is produced by beneficial bacteria (Lactobacillus Bulgarius, Streptococcus Thermophilus or both) that ferment the milk. These bacteria are present and active in the finished yoghurt. If they are added to the milk at the right temperature, they form lactose. This leads to thickening and produces lactose acid. Lactose acid gives the yoghurt its tangy flavour and preserves it. Before the invention of the fridge and before pasteurisation, this was the only way to preserve milk over a longer period of time.

Lactose acid can also be digested by people with lactose intolerance. Keeping it warm for seven hours produces yoghurt that is sufficiently thickened and not tart. The longer the yoghurt is left to ferment, the thicker it becomes, but the tart flavour becomes more intense. Depending on your personal preference, you can extend the fermentation time.