Standardisation of the solids-not-fat content in milk
The percentage of solids-not-fat (SNF) (mainly the lactose, protein and mineral matter) in milk for the manufacture of yoghurt is governed either directly by legal standards of the country concerned, or indirectly by the manufacturer seeking to produce an end product with certain physical properties and flavour. In the case of existing legal standards, the required solids-not-fat content in yoghurt ranges from
8.2 to 8.6g100g-1, and this minimum percentage seeks merely to protect the consumer; that is, the SNF level is roughly comparable to the level present in liquid milk. From the manufacturer’s point of view, the physical properties of yoghurt, for example, viscosity/consistency of the coagulum, are of
great importance and, in general, the higher the level of solids in the yoghurt mix the greater the viscosity/consistency of the end product. The relationship between the level of solids in the milk and the consistency of yoghurt was studied by Tamime (1977), and he observed that this property was greatly improved as the milk solids increased from 12 to 20g100g-1. Figure 2.4 shows this improvement in consistency as measured by the penetrometer. It must be emphasised that the greater the depth of penetration, the softer the coagulum and vice versa. However, the change in consistency between 16% and 20% tends to be less pronounced and hence there may be little value, in terms of product quality, in using a solids level above 16 g100g-1.