Yogurt is made by introducing specific bacteria strains into milk, which is subsequently fermented under controlled temperatures and environmental conditions (in fermentation tank), especially in industrial production.
The bacteria ingest natural milk sugars and release lactic acid as a waste product.
The increased acidity causes milk proteins to coagulate into a solid mass (curd) in a process called denaturation.
The increased acidity (pH = 4-5) also prevents the proliferation of potentially pathogenic bacteria.
In most countries, to be named yogurt, the product must be made with the bacterial species Streptococcus salivarius subsp. Thermophilus (ST) and Lactobacillus delbrueckii subsp. Bulgaricus.
Often these two are cocultured with other lactic acid bacteria for taste or health effects.
These include Lactobacillus acidophilus (LA), Lactobacillus casei, and Bifidobacterium species.
In the United States and in the European Union countries, a product may be called yogurt only if live bacteria are present in the final product.
In the United States, nonpasteurized yogurt can be marketed as “live” or containing “live active culture.”
A small amount of live yogurt can be used to inoculate a new batch of yogurt, as the bacteria reproduce and muliply during fermentation.
Pasteurized products, which have no living bacteria, may be called fermented milk product.
When yogurt is pasteurized, even though its main aim is to kill harmful bacteria, it kills large amounts of essential bacteria too, such as Acidophilus, Bifidus, and Lactobacillus rhamnosus.
Yogurt is a semisolid fermented milk product.
Its popularity has grown and is now consumed in most parts of the world.
Although the consistency, flavor, and aroma may vary from one region to another, the basic ingredients and manufacturing include ingredients, starter culture, and manufacturing methods.