There are many ways in which traditional cheeses can be classified. Criteria such as country of origin, type of milk used, species of animal used to produce the milk, fat content, moisture content, texture, whether mould ripened or not, cheese making process used, moisture in the non-fat solids have been and continue to be used. These criteria have been used either singly or in combination.

These descriptive approaches are limited in that they provide no theoretical insight into why one cheese is different from another.  In other words, why is Gouda cheese different than Cheshire or what makes Emmental different than Cheddar cheese?

For many years researchers in New Zealand, the UK, Ireland, the Netherlands and elsewhere were aware that there were significant differences in the pH and mineral concentrations of the major cheese varieties.

Lawrence et. al. (1984) first suggested that cheeses could be classified on the basis of two criteria, pH and calcium content. This approach is illustrated in fig. 1 for Swiss, Gouda, Cheddar and Cheshire cheeses.

When isolating phage in environmental samples it is important to realise that the phage population may consist of several phage strains with one common characteristic; they propagate on a particular host. Hence there is a need to obtain pure strains.

While the material below is particularly relevant to lactococcal phage isolation and purification it should be applicable to bacteriophages generally.