Solid-Not-Fat (SNF) is one of the most important quality parameters used in the evaluation and selection of milk for processing. It represents all the constituents of milk excluding water and milk fat, and primarily consists of proteins, lactose, minerals, organic acids, vitamins, and other minor solids. SNF significantly influences the nutritional value, density, processing characteristics, and yield of dairy products. Milk with adequate SNF content generally exhibits better processing performance and results in improved quality of products such as cheese, condensed milk, milk powder, and fermented dairy products.

The SNF content is also an important indicator of milk authenticity, as unusually low values may suggest adulteration through the addition of water or poor-quality milk. Since the density of milk is directly related to the concentration of dissolved solids, SNF can be estimated from the lactometer reading in conjunction with fat content. A lactometer measures the specific gravity of milk, which increases with increasing solids content and decreases with increasing fat content. Therefore, determination of SNF using a lactometer provides a rapid and convenient method for assessing milk quality at collection centres and dairy processing plants.

In this experiment, the lactometer reading is recorded at 40°C and subsequently corrected to obtain the corresponding value at the standard reference temperature. The corrected lactometer reading, together with the fat percentage, is used to calculate the percentage of solids-not-fat present in the milk sample.