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Unlock This CourseYoghurt is one of the oldest fermented foods in human history, dating back thousands of years. Today, it's both a popular food and an excellent example of how humans use microorganisms to create nutritious products. In this guide, we'll explore how bacteria transform milk into yoghurt through controlled fermentation.
Key Definitions:
Yoghurt production is a perfect example of biotechnology in action. It relies on the controlled growth of specific bacteria to transform milk into a thicker, tangy product. The main change happens when bacteria convert lactose (milk sugar) into lactic acid, which causes milk proteins to coagulate and form yoghurt's characteristic texture.
Two main bacteria are essential for yoghurt production: Lactobacillus bulgaricus and Streptococcus thermophilus. These work together in a symbiotic relationship - each produces compounds that help the other grow better. Together, they create yoghurt's distinctive flavour, acidity and texture.
Making yoghurt involves several carefully controlled steps, whether you're making it at home or in a large factory. The basic principles remain the same, though industrial production includes more sophisticated equipment and quality controls.
The process begins with high-quality milk (usually cow's milk). The milk is first pasteurised by heating to about 85°C for 30 minutes. This kills unwanted bacteria and denatures whey proteins, which helps create a thicker yoghurt. The milk is then cooled to around 43°C - the ideal temperature for yoghurt bacteria.
The starter culture containing Lactobacillus bulgaricus and Streptococcus thermophilus is added to the warm milk. These bacteria are carefully selected strains that produce the right flavour and texture. In commercial production, precise amounts are added to ensure consistent quality.
The inoculated milk is incubated at around 42-43°C for 4-7 hours. During this time, the bacteria multiply and convert lactose into lactic acid. The increasing acidity causes milk proteins (mainly casein) to coagulate, forming yoghurt's gel-like structure. The pH drops from about 6.8 to 4.5.
Once fermentation reaches the desired acidity level, several more steps are needed to create the final product:
In Bulgaria, where yoghurt has been made for centuries, traditional methods involve fermenting milk in clay pots. The natural bacteria present in these pots help create distinctive flavours. Modern factories, however, use stainless steel tanks that can hold thousands of litres, precise temperature controls and carefully selected bacterial strains. While industrial methods ensure consistency and safety, some argue that traditional methods produce more complex flavours.
Several factors can influence the quality of the final yoghurt product:
Temperature is critical throughout yoghurt production. If fermentation temperature is too low, the bacteria grow slowly, leading to longer production times. If too high, the bacteria may die or produce off-flavours. Most yoghurt bacteria work best at 42-45°C. After fermentation, proper cooling is essential to maintain quality during storage.
The length of fermentation affects both acidity and texture. Longer fermentation creates more acidic yoghurt with stronger flavour. However, over-fermentation can make yoghurt too sour and cause whey separation (syneresis). Commercial producers carefully monitor pH to determine the optimal stopping point.
The composition of the starting milk significantly affects yoghurt quality:
Yoghurt is not only delicious but also offers several health benefits:
Modern yoghurt production often incorporates additional probiotic bacteria beyond the traditional starter cultures. Strains like Lactobacillus acidophilus and Bifidobacterium species are added for their potential health benefits. These bacteria must survive both the yoghurt production process and passage through the stomach's acidic environment to reach the intestines where they can provide benefits. Manufacturers use special protective technologies and select acid-resistant strains to ensure these probiotics remain viable throughout the product's shelf life.
Large-scale yoghurt production follows the same basic principles as traditional methods but employs sophisticated technology to ensure consistency, safety and efficiency:
Different production methods create various yoghurt styles:
Fermentation occurs in the final container, creating a firm gel that's not disturbed. Greek yoghurt is a type of set yoghurt that's additionally strained to remove whey, resulting in higher protein content and thicker texture.
Fermentation occurs in large tanks, then the yoghurt is stirred and pumped into containers. This creates a smoother, more fluid texture that's common in fruit-on-the-bottom varieties.
Similar to stirred yoghurt but with more vigorous agitation and sometimes added water to create a pourable consistency. Popular in many countries as a convenient probiotic beverage.
Yoghurt production demonstrates several important biological concepts:
Understanding yoghurt production provides insight into how humans have used biotechnology for thousands of years, long before we understood the science behind it. Today, this traditional food continues to evolve with new technologies and scientific understanding, creating products that combine ancient wisdom with modern innovation.