Dairy Chemistry

Physical Properties of Milk

Freezing Point

The Freezing point depression is a measure used by dairy manufacturers to ensure that milk has not been adulterated either deliberately or by accident. Milk is paid for by the kilo and for dairy products manufacturers it is the solids content (Protein fat, lactose and minerals ) that is of use and water is mostly removed.

The freezing point is used to determine if added water is present


The freezing point of milk is usually in the range of -0.512° to -0.550° C with an average of about -0.522° C. Correct interpretation of the freezing point of milk requires an understanding of the factors affecting the freezing point depression. A cryoscope is used to freeze a given volume of milk which results in a very accurate and rapid evaluation result

Freezing point variations occur naturally and depend on the stage of lactation, health, breed and nutrition / feed of the cow
Typical Milk specification

Terms

  • Acid: Added as an acid and also lactose is converted into lactic acid by bacteria.
  • Acid curd: curd formed by the action of bacteria or by adding an acid, e.g. citric acid
  • Albumin: a water-soluble protein, a component of whey.
  • Annatto: orange-red dye used to colour cheese and butter
  • Bacteriophage: a virus that relies on a bacterial host for reproduction.
  • Brine: a solution of salt and water.
  • Casein: The main protein of milk.
  • Colostrum: the first milk secreted after giving birth.
  • Colony: a mass of individual cells
  • Disaccharide: e.g. lactose, a sugar composed of two monosaccharides.
  • Homogenise: to break down the fat globules in whole milk and distribute them evenly so that the cream in the milk does not separate.
  • Hypochlorite: (A bleach) chemical solution used after cleaning utensils to destroy micro-organisms.
  • Lactation: period during which milk is secreted.
  • Lactose: milk-sugar.
  • Lactic acid fermentation: The production of lactic acid from lactose by the action of micro-organisms.
  • Lipolytic: the property of splitting up or hydrolysing fat. Lipases are lipolytic enzymes; lipolytic bacteria are those that break down fat.
  • Mastitis: inflammatory condition of the udder.
  • Mesophiles: micro-organisms that have optimum growth temperatures between 25° and 45°C.
  • Organoleptic: testing the effects of a substance on the senses, especially of taste and smell.
  • HTST Pasteurisation: heating milk to 72°C for 15 seconds and cooling rapidly to less that 7°C.
  • Pathogenic bacteria: bacteria that cause disease or illness.
  • Rennet: enzyme which is used to coagulate milk in cheesemaking.
  • Polysaccharide: e.g. starch, cellulose. A complex carbohydrate of high molecular weight composed of many molecules of monosaccharides.
  • Proteolytic: protein splitting. Proteases are proteolytic enzymes; proteolytic bacteria are those that break down proteins.
  • Psychrotrophs: micro-organisms capable of growth at 5°C or below but their optimum growth temperature may be similar to mesophiles, i.e. 25°-45°C.
  • Starter: bacterial culture comprising selected strains and species of lactic acid bacteria used to produce the required acid and flavour development during the manufacture of fermented dairy products

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