Observe the following block of cheese, the depression in this cheese…

The correct answer is Option (3)- Release of CO₂ by Propionibacterium sharmanii.

Different varieties of cheese are known by their characteristic texture, flavour and taste, the specificity coming from the microbes used. For example, the large holes in ‘Swiss cheese’ are due to production of a large amount of CO₂ by a bacterium named Propionibacterium sharmanii.

The ‘Roquefort cheese’ are ripened by growing a specific fungi on them, which gives them a particular flavour.