Dairy yogurt is made when bacteria ferment the milk sugar, lactose, into lactic acid. This process thickens the milk and gives yogurt its characteristic tangy flavor.
Here's a breakdown of the process:
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Milk Preparation: The process typically begins with milk, which can be from cows, goats, or other mammals. The milk is often pre-treated, such as by adding milk solids or cream, to increase the protein and/or fat content. This helps improve the texture and richness of the final yogurt product.
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Heating: The milk is then heated to around 82-85°C (180-185°F) for several minutes. This heating step serves multiple purposes:
- Denaturing Proteins: It denatures the whey proteins in the milk, causing them to unfold and interact, which contributes to a firmer yogurt texture.
- Eliminating Undesirable Microorganisms: It kills off any undesirable bacteria that might be present in the milk and compete with the yogurt cultures.
- Reducing Whey Separation: Denaturing the proteins and creating the right environment prevents whey separation, the watery layer sometimes seen on top of yogurt.
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Cooling: After heating, the milk is cooled to a temperature of around 40-45°C (104-113°F). This is the optimal temperature range for the yogurt cultures to thrive.
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Inoculation (Adding Cultures): This is the crucial step where specific strains of bacteria, known as yogurt cultures, are added to the cooled milk. The two main bacteria cultures used are Streptococcus thermophilus and Lactobacillus bulgaricus. These cultures are responsible for fermenting the milk.
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Incubation: The inoculated milk is then incubated at a controlled temperature (usually around 40-45°C or 104-113°F) for several hours. During this incubation period, the bacteria consume the lactose (milk sugar) and produce lactic acid as a byproduct.
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Acidification and Coagulation: As the bacteria produce lactic acid, the pH of the milk decreases, making it more acidic. This acidity causes the milk proteins (primarily casein) to coagulate, or clump together, forming a semi-solid gel structure—the yogurt.
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Cooling and Storage: Once the yogurt has reached the desired consistency and acidity, it is cooled to stop the fermentation process. Cooling slows down the activity of the bacteria, preventing the yogurt from becoming too sour. The yogurt is then stored under refrigeration to maintain its quality and freshness.
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Flavoring and Packaging (Optional): At this stage, flavorings, fruit, sweeteners, or other additives may be added before packaging and distribution.
In essence, dairy yogurt production is a fermentation process driven by specific bacteria that transform milk into a thicker, tangier, and more digestible product.
