🥛 Dairy Products: Drinking Milk and Soured Milk
- 1. Drinking Milk (Fluid Milk)
🔹 Definition
Drinking milk (also called fluid milk) is milk processed for direct human consumption. It is usually subjected to heat treatment and mechanical processing to ensure safety, stability, and good sensory qualities.
🔹 Main Processing Steps
Clarification and filtration – removal of impurities and somatic cells.
Standardization – adjustment of fat content to meet specific product requirements.
Pasteurization – heat treatment (e.g., 72 °C for 15 seconds) to destroy pathogenic microorganisms.
Homogenization – mechanical treatment to break down fat globules, preventing cream separation and improving texture.
Fortification (optional) – addition of vitamins and minerals, commonly vitamin D and calcium.
Cooling and packaging – to maintain freshness and extend shelf life.
🔹 Types of Drinking Milk
Whole milk – natural fat content (~3.2% fat).
Reduced-fat milk – 1–2% fat.
Skimmed milk – less than 0.5% fat.
Flavoured milk – e.g., chocolate, vanilla, strawberry.
UHT milk (Ultra-High Temperature) – processed at 135–150 °C for a few seconds, giving longer shelf life.
- 2. Soured Milk (Fermented Milk)
🔹 Definition
Soured milk (also called fermented milk) is milk that has undergone controlled fermentation by lactic acid bacteria (LAB). These bacteria convert lactose into lactic acid, reducing pH and causing milk proteins to coagulate. The result is a product with a sour taste, thicker texture, improved digestibility, and probiotic properties.
🔹 Fermentation Process
Heat treatment of raw milk – usually pasteurization, to destroy undesirable microbes.
Cooling to incubation temperature – about 30–45 °C, depending on the starter culture.
Inoculation – addition of starter cultures (e.g., Lactobacillus bulgaricus, Streptococcus thermophilus).
Fermentation – lactose → lactic acid, pH decreases to ~4.6.
Cooling and packaging – to stop fermentation and maintain product stability.
🔹 Examples of Fermented Milk Products
Yogurt – produced with Lactobacillus bulgaricus and Streptococcus thermophilus.
Kefir – contains both bacteria and yeasts; slightly carbonated and alcoholic.
Buttermilk – obtained after churning cream into butter or cultured with LAB.
Clabber (traditional sour milk) – naturally soured milk without added starter culture.