Yogurt Definition and Composition
📌 Yogurt is a product of pasteurized milk fermented by specific bacteria (like *Lactobacillus bulgaricus* and *Streptococcus thermophilus*) to achieve a distinct flavor and texture without added stabilizers or colors.
🥛 Nutritionally, yogurt is nearly equivalent to milk, containing carbohydrates, fats, protein, vitamins, minerals, and energy.
🔬 Fermentation is defined as the chemical structure change in organic materials using biological agents, mainly enzymes, as biocatalysts.

Yogurt Preparation Process (Experimental Setup)
🧪 The demonstration involved mixing 200 ml of full-cream UHT milk with 40 ml of low-fat milk (total volume 240 ml) and inoculating it with an 80 ml starter (which is 30% of the total mixture volume).
🔥 The mixed milk must be heated to 85°C (indicated by "crab eye bubbles") for pasteurization, then cooled down to 40°C before inoculation.
⏳ The mixture was incubated at room temperature for six hours in a closed container.

Incubation Results and Analysis
📉 After six hours at room temperature, the bottom layer of the yogurt had coagulated (clumped), while the top layer remained slightly liquid or thin.
🌡️ The coagulation at the bottom is attributed to room temperature affecting viscosity due to fat globule clumping (according to Meryati and Kusnadi, 2011).
⏱️ For full setting at room temperature ($\approx 20-25^\circ \text{C}$), incubation typically requires 14-16 hours (according to Prasetyo, 2017), indicating that six hours was insufficient for complete solidification.

Biochemistry of Fermentation
🦠 The beneficial bacteria (*L. bulgaricus* and *S. thermophilus*) break down lactose in milk into lactic acid, which lowers the milk's pH and increases acidity.
🧀 This acidity causes the milk casein protein to destabilize and coagulate, forming the yogurt gel structure.
🛡️ Due to lactose conversion to lactic acid, yogurt can be consumed by individuals with lactose intolerance and the elderly.

Factors Affecting Yogurt Texture
🧬 Key factors influencing yogurt texture include the fat content of the milk before inoculation and nutrient availability.
🔬 The amount of starter culture used directly correlates with thickness; a larger starter volume results in a thicker yogurt due to a lower resulting pH value.
🚫 The presence of antibiotics in the milk is also cited as a factor that can negatively influence the process.

Key Points & Insights
➡️ Yogurt production requires precise temperature control: pasteurizing to 85°C and cooling for inoculation to 40°C.
➡️ The starter culture ratio is crucial; using a larger starter (e.g., 30% concentration) promotes faster coagulation and increased thickness by lowering the final pH.
➡️ Achieving a fully set yogurt at room temperature requires significantly longer incubation, approximately 14-16 hours, compared to the tested six hours.

📸 Video summarized with SummaryTube.com on Nov 13, 2025, 08:07 UTC