Dairy Science

Processing Methods for Liquid Milk

• Standardization:

  • Definition: The process of adding skim milk to adjust and reach the desired fat content level in fluid milk.

• Pasteurization:

  • Definition: Thermal processing of milk by heating to kill pathogenic bacteria.

  • Primary Purpose: To protect public health and ensure microbiological safety.

  • Thermal Processing Regimes:

  • LTLT (Low Temperature Low Time): Heating milk to $145^\circ\text{F}$ for $30\,\text{minutes}$.

  • HTST (High Temperature Short Time): Heating milk to $161^\circ\text{F}$ for $15\,\text{seconds}$.

  • UHT (Ultra-High Temperature / Flash Pasteurization): Heating milk to $280^\circ\text{F}$ for $2\,\text{seconds}$.

  • Microbiological Impact of UHT: Kills beneficial (good) bacteria in addition to pathogenic organisms.

• Homogenization:

  • Definition: The physical reduction of fat globule size to prevent cream separation from the fluid milk.

  • Process Mechanism: Pumping milk through fine screens under high pressure.

• Separation:

  • Definition: The application of centrifugal force to separate milk into its distinct components (fluid milk and cream).

• Ultrafiltration:

  • Definition: A membrane separation process used to isolate milk components based on molecular size.

• Reverse Osmosis:

  • Definition: A concentration process that isolates milk components by removing water under pressure.

Storage Conditions and Quality Grading of Milk

• Milk Storage Conditions:

  • Cooling: Milk must be cooled and stored at temperatures strictly below $40^\circ\text{F}$.

  • Sanitary Environment: Facilities and handling systems must maintain strict sanitary conditions.

  • Odor Control: Storage areas must remain completely odor-free, as milk readily absorbs ambient odors.

  • Light Protection: Milk must not be exposed to direct sunlight or fluorescent light to prevent light-induced oxidation and flavor degradation.

• Milk Quality Grading:

  • Grading Criteria: Based on facility standards and sanitary conditions maintained at the farm level.

  • Grade A Milk:

  • Represents over $90\%$ of all milk produced in the United States.

  • Designated specifically for fluid milk consumption.

  • Grade B Milk:

  • Designated for manufactured dairy products.

  • Examples of Grade B applications: Production of butter and dry powdered milk.

Dairy Product Classifications and Compositional Standards

• Fluid Milk and Cream Categories:

  • Skim Milk: Standardized to contain less than $0.5\%$ milkfat ($< 0.5\%$ fat).

  • Low-Fat Milk: Standardized to contain $1\%$ milkfat.

  • Reduced-Fat Milk: Standardized to contain $2\%$ milkfat.

  • Fortified Milk (Skim + Low-Fat Milk):

  • Solids Non-Fat (SNF): Milk solids are added back in to bring SNF content up to 10.25\%$.\n - Nutrients and Additives: Enhanced with flavorings and fortified with Vitamin A and Vitamin D.\n - **Cream**:\n - Fat Content Range: Contains between 10.5\%$and$36\% milkfat, offering a wide array of commercial options.\n\n- **Manufactured and Cultured Dairy Products**:\n - **Ice Cream**: Must contain at least 10\% milkfat by regulatory standards.\n - **Sherbert**: Features lower fat and lower milk solids content than ice cream, but contains higher sugar content.\n - **Butter**: Standardized to contain at least 80\% milkfat.\n - **Eggnog**:\n - Formulation: Prepared from milk, eggs, and sweetener.\n - Fat Content: Contains 6\% milkfat.\n - **Cheese**:\n - Variety: Encompasses over 400+ distinct varieties.\n - Production: Manufactured using microorganisms.\n - **Yogurt**:\n - Fermentation Process: Produced via lactic acid fermentation using bacterial cultures.\n - **Greek Yogurt**: Higher in protein content than standard yogurt; requires a 4:1$milk volume ratio ($4\,\text{units}$of milk per$1\,\text{unit} of Greek yogurt) compared to conventional yogurt.\n - **Cultured Dairy Products**:\n - Definition: Products that utilize microorganisms during production.\n - Starter Cultures: Specific starter cultures are used to introduce beneficial microbes.\n - Examples: Yogurt, sour cream, and cheese.\n\n\n# Raw Milk Yields in Dairy Manufacturing\n\n- **Milk Input Requirements per Unit of Product**:\n - **Butter**: Requires 21.2\,\text{lbs}$of whole milk per$1\,\text{lb} of butter.\n - **Cottage Cheese**: Requires 6\,\text{lbs}$of whole milk per$1\,\text{lb} of cottage cheese.\n - **Ice Cream**: Requires 12\,\text{lbs}$of whole milk per$1\,\text{gallon} of ice cream.\n - **Cheese**: Requires 10\,\text{lbs}$of whole milk per$1\,\text{lb} of cheese.\n\n\n# Non-Dairy Product Classifications\n\n- **Imitation Products vs. Substitute Products**:\n - Definition of Imitation Products: Formulated to look and taste like authentic dairy products.\n - FDA Classification: Defined by the Food and Drug Administration (FDA) as nutritionally inferior to real dairy products.\n - Characteristic Ingredients: Contain water and corn syrup as major formulation components.\n\n\n# Health and Nutritional Aspects of Dairy Consumption\n\n- **Lactose Intolerance**:\n - Etiology: Caused by a deficiency in the lactase enzyme, which is needed to break down lactose.\n - Prevalence: Relatively common worldwide.\n - Management Options: Consuming smaller serving sizes, taking lactase enzyme tablets, and selecting reduced-lactose products.\n\n- **Milk Allergy**:\n - Etiology: An immune system reaction to milk protein.\n - Epidemiology: Affects between 2\%$and$3\%$of children under age 3 ($2\% - 3\%).\n - Prognosis: Most affected children outgrow the allergy.\n\n\n# Avian Egg Biology and Composition\n\n- **Biological Function and Comparative Size**:\n - Primary Purpose: Biological reproduction.\n - Comparative Size: Bird eggs are smaller than mammalian eggs.\n\n- **Egg Composition (Percentage by Weight)**:\n - **Shell**: Accounts for 11\% of total egg weight.\n - **Yolk**: Accounts for 31\% of total egg weight.\n - **Albumen (Egg White)**: Accounts for 58\%$$ of total egg weight.