How yogurt is made
Two bacteria that cooperate turn milk into yogurt in as little as 4 hours.
- stations
- 6
- things upstream
- 11
- raw sources
- 7
- steps from the ground
- 3
The short version
Milk is standardized, often with added milk powder, then heated hard and cooled to incubation temperature. Two bacteria, Lactobacillus bulgaricus and Streptococcus thermophilus, are mixed in and the milk is held warm for 4 to 12 hours. Acid builds, the proteins set, and the yogurt is cooled, flavored and packed.
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Fortify the milk
Milk is balanced for fat, and dried milk is often added because extra solids make a firmer yogurt. Cow milk is typical, but goat, sheep and camel milk set differently.
Goes in -
Heat it hard
The milk is held hot, well past the heat of normal pasteurization. The heat kills pathogens and unfolds the whey proteins so they bind to the casein and make a thicker, smoother set.
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Cool and inoculate
Milk is cooled to a comfortable fermenting temperature and the starter culture is mixed in. The two main bacteria are Lactobacillus delbrueckii bulgaricus and Streptococcus thermophilus, and they help each other grow.
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Incubate until it sets
The milk is held at 30 to 45 °C for 4 to 12 hours. Bacteria turn lactose into lactic acid, the acid curdles the casein, and the milk gels. Higher temperatures work faster but risk a lumpy texture.
4 to 12 hours
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Stir or leave set
For set-style yogurt, the milk is poured into cups before incubation and sets right in the container. For Swiss-style, the finished gel is stirred smooth in a vat before it is packed.
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Flavor and fill cups
Fruit, sweeteners, and sometimes starch, pectin or gelatin are blended in. The yogurt is filled into cups, sealed and chilled quickly to slow the fermentation.
Worth repeating
- In 1905 the Bulgarian medical student Stamen Grigorov isolated the bacterium now known as Lactobacillus delbrueckii bulgaricus from soured milk from his home village.
- Yogurt with fruit jam at the bottom was patented in 1933 by a dairy in Prague.
Back to the ground
Follow every input upstream and yogurt starts as these 7 raw sources.
Everything it is made of See it on the map
Open the whole family tree
Keep walking
Sources
Cite this page: "How yogurt is made." Assembly Line, 2026-11-03. https://assemblyline.org/make/yogurt