A 500 ml batch of curd is prepared using a starter containing Lactobacillus delbrueckii subsp. bulgaricus. The culture ferments lactose at a rate of 0.018 g per litre per hour. If fermentation proceeds for 4 hours, how many grams of lactose are converted to lactic acid?
Answer
0.036 g
The correct answer is 0.036 g — Thus 0.036 g of lactose are converted.
Step-by-step solution
- Convert the batch volume to litres: 500 ml = 0.5 L.
- Calculate lactose fermented per hour: 0.5 L × 0.018 g L⁻¹ h⁻¹ = 0.009 g h⁻¹.
- Multiply by the fermentation time: 0.009 g h⁻¹ × 4 h = 0.036 g.
- Thus 0.036 g of lactose are converted.
Common mistake: Using 500 ml directly without converting to litres, leading to a value 1000 times larger
Concept tested: Quantitative calculation of lactose fermentation
Published · How this solution was prepared and checked
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