Why are there holes in some cheese?
Gas bubbles formed during bacterial fermentation when certain cheeses (Emmentaler, Gruyere) are made lead to holes in these cheeses.
Read on for more info:
In some cheese, bacterial cultures that produce gas bubbles during the fermentation process are used on purpose. The gas bubbles lead to holes forming throughout the cheese, usually during the ripening process, and can vary in size and shape. Propionic acid bacteria are often added during the cheese making process to create larger, more uniform holes. The resultant propionic acid also adds a sweet, nutty flavour to such cheese. Other types of bacteria can, however, also be used to make holey cheese.