Experimental method:

Everyone who has eaten yogurt knows that the fragrant yogurt is not only sweet in taste, but also very rich in nutrition. It is easily digested and absorbed, and it is a nutritious food loved by men, women and children.

Can we make yogurt ourselves? Can! The method is also very simple, you can have a try.

1. Make yogurt with fresh milk.

Put a bottle (250g) of fresh milk into a small milk pot, add one or two spoonfuls of white sugar, boil it, cover it, cool it to about 35℃ (that is, it is not hot), and pour this warm milk into a clean covered container (drinking cup, tea cup, tea jar, can bottle, etc.) prepared in advance and scalded with boiling water.

Then add two or three spoonfuls of yogurt as a strain, and cover it tightly after stirring. Wrap the container with towel or cotton wool and put it in an environment of 30℃ (next to radiator or stove) for fermentation. Under normal circumstances, after 8 hours of fermentation, the milk will solidify and produce sour flavor. At this time, yogurt is made. You can put it in the refrigerator or cold water to cool it, and it will taste more delicious.

2. Make yogurt with milk powder.

Where fresh milk is scarce, milk powder can also be used to make yogurt. Take one or two whole milk powders, add 24 grams of sugar, and mix with 500 grams of water to make sweet milk. After boiling, take off the milk pan, cover it, and when it is cool enough to not burn your hands, you can pour it into the prepared container and add two or three spoonfuls of yogurt as a strain. The fermentation time is also about 8 hours.

Using sugary instant whole milk powder to make yogurt, the amount of milk powder should be more and the amount of sugar should be less. The other processes are exactly the same.

Please note that no matter which method is used to make yogurt, homemade yogurt can also be used as a strain. However, after two or three consecutive uses, you need to switch to the yogurt you bought as a strain.

Why do you want to switch to strains? Because the pure strain of artificially cultured "Bulgarian lactic acid bacteria" was added to the bought yogurt. When this bacterium grows and breeds in milk, it can turn lactose in milk into lactic acid and make milk sour; It can also decompose the protein in milk into various amino acids, which makes the milk fragrant, thus improving the nutritional value of milk. In this way, a large number of lactic acid bacteria are propagated in the yogurt, which can be used as strains. However, in the process of homemade yogurt, it is inevitable to bring in miscellaneous bacteria because of lax disinfection and sterilization. After inoculation again and again, the amount of miscellaneous bacteria will continue to increase, so in order to ensure the quality of homemade yogurt, we must switch to pure bacteria.

Knowledge extension:

It is said that yogurt originated in Bulgaria. In the past, there were many nomadic Thracians in Bulgaria, who often carried skins filled with goat's milk on their backs. Due to the effect of body temperature, milk often turns into tofu brain. If a small amount of sour milk is poured into the cooked milk, it will "infect" the fresh milk, and all the cooked milk will become sour.

At first, people were afraid to drink these yoghurts. Later, bold people tasted it and found that yogurt was not only drinkable, but also delicious. So they are constantly looking for new ways to process yogurt: some add sour bread to milk, and some add sour wild plants to milk to make milk sour. This is the earliest artificial yogurt.

1784, two Turks spread Bulgarian yogurt to the United States and later to Europe. However, because the sour taste is too strong and the sweetness is insufficient, people have not paid attention to it for a long time.

At the beginning of the 20th century, Russian scientist I Menchinikov found that human large intestine is very suitable for the survival of corrupt bacteria, which is an important reason for human premature aging and shortened life. In order to deal with this bacteria, he has investigated the longevity of the elderly in many countries. In Bulgaria, he found that there were four centenarians in every 1000 dead. And they all loved to eat yogurt before they died. Later, he found a kind of bacteria in Bulgaria's yogurt, which can effectively eliminate the spoilage bacteria in the large intestine. He called this kind of bacteria "Bulgarian lactic acid bacteria".

When the Spanish businessman Isaac carazo knew the secret, he managed to buy strains from Bulgarian and German Pasteur Institute and began to produce yogurt. And it is also sold in pharmacies as a longevity drug.

After the outbreak of World War II, carazo established a yogurt factory in the United States and began to sell yogurt as food. Because yogurt tastes sweet and sour, more and more people like it, and it has gradually become a popular food.

In the ancient agricultural book Qi Min Yao Shu published in the 6th century AD, the method of making yogurt with goat's milk or milk was also recorded in detail. And it has been recognized that yogurt can be made by inoculating fresh milk, which is very similar to the method we use today. At that time, it was also recognized that temperature was a very important factor in making yogurt. However, there was no further research and promotion.