Raw milk cheese

October 2008

Dr David Everetts (Senior lecturer in Food Science, Otago University) specialist interest is dairy food chemistry, particularly cheeses. With the growth of the food service industry, Mozzarella has become as important as cheddar. In the recent past Dr Everett completed work on the functional properties of Mozzarella cheese to extend its shelf life. In particular, he worked on ways of encapsulating the fat within the protein structure so that it would not exude oil during stretching and heating.

Some aspects of this work are now being extended into what is a new area for NZ raw milk cheeses.

Until recently it has been stiff cheese for lovers of cheeses made from raw milk. Previously, cheese sold in NZ had to be made from pasteurised milk that had been heat-treated to kill potentially dangerous pathogens such as Listeria and Salmonella.

However, last year the NZ Food Safety Authority changed the rules to allow the importation of a limited variety of cheeses made from unpasteurised milk. The Authority is now looking at changing its regulations again to allow cheese from raw milks (i.e. not just cows milk) to be made in New Zealand, and there is considerable interest amongst specialty cheese makers in getting into this novel and potentially lucrative niche.

What is different about raw milk cheeses?

Their stronger flavour and greater food value, according to aficionados. Pasteurisation denatures some enzymes involved in flavour development, and some that are considered nutritionally valuable.

Imported raw milk cheeses include Roquefort, and hard cheeses from Switzerland and Italy.

The catch is that untreated milk could potentially contain harmful organisms, and while the health risk is not considered serious for healthy people, it could cause serious harm to infants and young children, the elderly, pregnant women and their foetuses, and people with impaired immune systems. Advocates of raw cheeses point to their successful manufacture in Europe and elsewhere for centuries, but tight regulations covering the source and processing of raw milks are likely.

It is the flavour profile of these cheeses that interests Dr Everett, and he is starting a research programme to look at flavour differences between the raw milk cheeses and the corresponding pasteurised milk cheeses.

It is not work that has been covered elsewhere in the world because mostly they either make raw milk cheese or the pasteurised milk version and do not do the flavour comparisons, he says.

We have just started the work this year looking at cheese made from raw milk and from milk treated at several different temperatures, and looking at what volatiles have come through that are different to those from regular cheese.

Gas Chromatograph Olfactometry (GCO) is used, which involves a device that drives off volatile compounds. Panelists chosen for their ability to discriminate smells readily sniff volatiles emanating from a tube and describe them, identifying those that may be important to aroma and flavour perception. The testing is done in bursts because after about 20 minutes even the best trained noses become desensitised.

Knowing how cheese raw material and structure affect flavour will become important to developing methods of enhancing desirable characteristics and eliminating undesirable ones when the raw milk cheese industry gets under way in NZ.

Improving the flavour of low-fat cheeses

About a third of the fat in cheddar cheese can be removed before the flavour starts to become unacceptable. Beyond that the cheese becomes very hard and loses a lot of the flavour components that are associated with cheddar.

Reducing the fat content is desirable from a public health point of view, so Dr Everett and co-workers are working on ways of removing around 50% of the fat and then adding back the flavour to fat-reduced cheddar.

The research that I am looking at now is not on the fat so much it is what covers the fat, an encapsulating protein phospholipid layer. We can readily extract the fat from milk, and what we want to do is add back healthier alternatives such as a vegetable oil that is encapsulated in the natural milk protein membrane, he says.

We can even use mineral oil, so it shows that it is not the fat that is important but the covering around it. We have used this sort of technique to improve the flavour of yoghurt in past research.