FSTC 101 - Milk & Milk Products

Milk & Milk Products

  • Milk is consumed as fluid or used as raw material for various products.
  • Principal constituents:
    • Fat
    • Protein
    • Lactose (milk sugar)
    • Minerals (ash)
  • Variability in milk composition exists among different animal species.
  • Processing conditions suitable for cow's milk may not be optimal for milk from other sources.
  • Cow's milk composition varies based on breed, age, lactation stage, season, feed, drugs, etc.
  • Milk is highly regulated as a food commodity.
  • Fat content standards are legally regulated (e.g., 3-3.8%).
  • Proper handling is essential for health due to potential disease transmission.

Milk Production

  • Milk is produced in the udder from components extracted from the bloodstream.
  • Milking machines use vacuum to extract milk from teat canals.
  • Milk is rapidly cooled to ±4.4°C or lower to inhibit bacterial spoilage.
  • Milk from a healthy udder is initially sterile.

Milk Testing

  1. Fat and total solids determination (chemical or physical analysis).
  2. Sediment estimation (filtration).
  3. Bacterial counts (coliform, mold, yeast).
  4. Freezing point determination (detects added water).
  5. Flavor evaluation.
  6. Antibiotic detection.

Milk Processing

  • Clarification
  • Pasteurization
  • Homogenization

Clarification

  • Milk is passed through a centrifugal clarifier to remove sediment, body cells, and some bacteria.
  • Clarification doesn't completely eliminate bacteria (Bactofuge).

Pasteurization

  • Aims to eliminate disease-producing organisms.
  • Destroys lipase and other natural milk enzymes.
  • Targets:
    • Mycobacterium tuberculosis (heat-resistant, non-spore forming): 62°C for 30 min.
    • Coxiella burnetti: 63°C for 30 min.
  • Methods:
    • Batch (holding) method: ≥63°C for ≥30 min.
    • High-temperature-short-time (HTST): ≥72°C for ≥15 sec.
  • Pasteurized milk isn't sterile; requires rapid cooling after pasteurization.
  • Slight vitamin destruction may occur, but no objectionable cooked flavor.

Homogenization

  • May occur before or after pasteurization.
  • Milk contains numerous fat globules that tend to clump and rise due to density.
  • Skim milk has virtually no fat globules.
  • Purpose: To subdivide fat globules to prevent creaming (rising to the top).
  • Results in more uniform milk, richer taste, whiter color, and greater whitening power.

Bovine Growth Hormone (BGH) / Bovine Somatotropin (BST)

  • Injection of pituitary gland extract in the 1950s increased milk production.
  • Protein responsible: BGH/BST.
  • Also responsible for increased growth rate in young animals.
  • Initially considered for treating dwarfism.
  • Gene transfer into bacteria allowed inexpensive BGH production.
  • Injecting BGH into lactating cows can increase milk production by 10-15% with greater feed efficiency.

Ice Cream

  • Dairy ingredients: whole milk, skim milk, cream, frozen cream, butter, butter oil, condensed milk, dried milk products.
  • Composition: milk fat, milk solids non-fat (MSNF), sugar, stabilizer, emulsifier, flavoring, water, and air.
  • Milk fat is the most expensive ingredient; higher fat content increases product cost.
  • Air is whipped in to prevent excessive density, hardness, and coldness.
  • Overrun: increase in volume from air incorporation during freezing.
  • Overrun calculation: (V2–V1V1)⋅100(\frac{V2 – V1}{V1}) \cdot 100

Ice Cream Manufacturing Procedure

  1. Pasteurization
  2. Homogenization
  3. Ageing the mix
  4. Freezing
  5. Ice cream hardening
Pasteurization
  • Mix is pasteurized via batch or continuous heating.
  • Pasteurization temperatures are higher than for plain milk.
Homogenization
  • Breaks up fat globules, preventing churning into butter granules during freezing.
  • Improves overall body and texture.
Ageing the Mix
  • Mix is held for 3-24 hours at 4.4˚C.
  • Melted fat solidifies, stabilizers swell and combine with water, increasing viscosity.
  • Leads to quicker whipping, smoother texture, and slower melt-down.
Freezing
  • Quick freezing is necessary to prevent large ice crystal formation.
  • Mix is frozen and whipped in a freezer cylinder in ≤30 seconds to -5.5˚C.
  • Semi-solid ice cream is packaged immediately.
Ice Cream Hardening
  • Temperature is about -34 ˚C.
  • Freezes most of the remaining water, making the ice cream stiff.

Cheese

  • Product made from milk curd, coagulated with enzyme (rennin/chymosin) or acid (lactic acid).
  • May involve heat, pressure, salt, and ripening with selected microorganisms.
  • Milk components: fat, proteins, lactose, minerals, and water.
  • Adding acid/rennin causes casein to coagulate, trapping fat, lactose, water, and minerals in the curd.
  • Remaining liquid (whey) contains dissolved lactose, proteins, minerals, and minor constituents.
  • Cheese curd can be made from raw or pasteurized milk.
  • Raw milk cheese must be ripened for ≥60 days.

Cheese Making Process

  1. Setting the milk
  2. Cutting the curd
  3. Cooking
  4. Draining whey & matting curd
  5. Milling & salting
  6. Pressing
  7. Curing or ripening
Setting the Milk
  • Pasteurized whole milk is heated to 31˚C in a vat.
  • Lactic acid-producing starter culture (S. lactis) is added.
  • Natural color may be added.
  • After 30 min, rennin is added as a dilute solution in mildly acidic conditions.
  • Acidic conditions promote rennin coagulation.
  • Stirring is stopped, and milk sets for ±30 min to form curd.
  • Rennin and acid create an elastic curd that shrinks when heated/pressed, expelling whey.
Cutting the Curd
  • Curd knives (wires strung across a frame) are used.
  • Smaller cubes result in quicker and more complete whey removal, producing drier cheese.
Cooking
  • Cubes are agitated, and vat is heated to raise curd and whey temperature.
  • Temperature is raised to 38˚C over 30 min and held for 45 min.
  • Cooking helps squeeze whey from curds and increases acid production.
Draining Whey & Matting Curd
  • Agitation is stopped, and curds settle as whey is drained.
  • Curds are allowed to mat, forming a continuous slab.
Milling & Salting
  • Slabs are cut into small pieces by a mill.
  • Milled pieces are spread and sprinkled with salt (2.5% of curd weight).
  • Salt and curd are stirred for even distribution.
  • Salting purposes:
    1. Draw out whey via osmosis.
    2. Inhibit spoilage organisms.
    3. Add flavor.
Pressing
  • Milled and salted curds are placed in cheese cloth-lined hoops and pressed.
  • Pressing determines the final cheese moisture content.
  • More retained moisture leads to more acidity from fermentation, affecting texture and microorganism growth during ripening.
Curing or Ripening
  • After pressing overnight, cheese is removed from hoop and placed in a cool room for surface drying.
  • Cheese is dipped in paraffin or vacuum-sealed to prevent mold growth and excessive drying.

Specific Cheese Types

  • Blue Veined Cheese: Inoculated with Penicillium roqueforti or Penicillium glaucum spores, punctured to allow mold penetration, creating veins or pockets of mold.
  • Swiss Cheese: Nutty flavor and large holes from Propionibacterium shermanii activity. Propionic acid provides flavor, CO2 forms pockets.
  • Cottage Cheese: Low-fat soft cheese coagulated with lactic acid (not rennin). Curd remains particulate, unpressed, unaged, and unrefrigerated. Highly perishable.