Cheese makers understand that the sensory value of cheese plays an important role in the consumer's choice of cheese and whether it is enjoyed. However, it is not only the taste that counts. Cheese flavour, as one of the sensory values, is a combination of taste, aroma, heat, cold and tactile sensations. It is assessed through analysing the volatile and non-volatile compounds in cheese; over 100 of these have been identified. Volatile compounds are assessed in the nose at the olfactory receptors, via the orthonasal or retronasal routes and non-volatile compounds on the tongue as taste, mounthfeel and texture. Cheese flavour is an important quality attribute, and although the type of milk and manufacturing method play roles, it is mainly formed during the curing stage hence the fact that fresh cheese is fairly bland.

The cheeses of the world, although all belonging to only about ten categories, possess a wide spectrum of flavours. Firstly the flavour is determined by the milk origin; cow, goat, sheep or mixtures thereof. Goat's milk for instance contain three times more of the fatty acids capric, caproic and caprylic than cow's milk; enough reason to give goat's milk cheese a distinctive flavour difference.

Secondly, the manufacturing method of each cheese plays an important role in the subsequent metabolisms, which will determine the end flavour. Milk treatments such as pasteurization, or not, the selection of microorganisms and enzymes in the culture, added to the milk, and how much moisture is driven from the curd during the manufacturing process, all play an important role in the final flavour.

Thirdly, and in my opinion the most import, is what happens during the curing period. During this period, which can last from one week to two years, the environment is controlled with temperature, humidity and airflow to allow specific biochemical changes to take place. These changes together with microbiological changes will decide the flavour and texture of the cheese.

Compounds formed from protein, carbohydrates and milk fat are essential for cheese flavour. Before, but mainly during curing, free fatty acids, lactones, ketones, esters, alcohols and aldehydes are formed from milk fat, which all contribute to the final cheese flavour. Characteristic flavours for each type of cheese, or individual cheeses of a type, are related to the concentrations and balance of these broken down products.

As cheese makers, we are struggling to relate the characteristic flavour of a specific cheese to a single or group of these compounds however, some progress has been made. For instance, today we know that the concentration of free fatty acids and hydrogen sulphide play an important role in the desired flavours of Parmesan and Cheddar and a lesser role in the case of Mozzarella and Camembert. Propionate and acetate, derived from Propionibacterium freudenreichii bacteria used in the culture when making Emmental, have proved to be essential to impart the nutty and sweet flavour of this famous Swiss cheese. At the same time, the carbon dioxide metabolism by the P. freudenreichii gives the typical holes.

Although we know that the lipolysis, proteolysis and metabolisms which take place during curing are largely responsible for cheese flavour, we also know that there is still much too learn about these microbiological and biochemical events.