Final answer:
The production of fruit curd is a biological fermentation process where warmed milk is combined with preformed curd containing microbes. These microbes convert lactose into lactic acid, which curdles the milk at a specific pH. The process is anaerobic and the curd forms within 4-12 hours depending on the temperature, with 37°C being the ideal incubation temperature.
Step-by-step explanation:
The procedure for making fruit curd involves the fermentation of milk through the action of microorganisms. To begin, milk is warmed to maintain the temperature needed for the growth of microbes such as Lactobacillus cecai, which are commonly found in preformed curd. The warmed milk is then combined with the preformed curd, stirring it to distribute the microbes evenly. The aeration of the mixture is anaerobic, meaning it doesn’t require oxygen and is thus performed in a closed container. The lactose in milk is enzymatically converted into glucose and galactose, with glucose further breaking down into lactic acid via the glycolytic pathway. This lactic acid production reduces the pH of the milk to around 4.5, which is the isoelectric pH of the milk protein casein, causing it to precipitate and curdle the milk to form curd. This process of fermentation is sensitive to temperature; during the summer, curd forms within 4-6 hours, but in the rainy season, it takes 6-8 hours, and in winter, up to 8-12 hours. The specific temperature ideally maintained for the incubation of the curd is usually around 37°C. The process utilized here is an example of batch fermentation technology, using a simple fermentor or bioreactor like a mud pot or a steel vessel to create the curd.