Judging and Grading of Milk

Judging and grading of milk are processes used to assess its quality, safety, and suitability for consumption or processing. These evaluations are based on sensory, physical, chemical, and microbiological criteria. While "judging" often refers to sensory evaluation (e.g., taste, smell) in competitions or informal settings, "grading" is a formal, standardized classification tied to regulatory and industry benchmarks. Here’s how it works:

Judging Milk (Sensory Evaluation)

This is typically a hands-on assessment of milk’s organoleptic properties—how it looks, smells, and tastes. It’s common in dairy competitions (like 4-H or state fairs) or quality control troubleshooting.

1. Appearance:

   • Color: Fresh cow’s milk should be white to slightly creamy. Yellowish tints might indicate high carotene (from grass-fed cows) or contamination. Blue/green hues suggest bacterial issues (e.g., Pseudomonas).

   • Clarity: Should be free of sediment, clots, or floating particles.

2. Odor:

   • Fresh milk has a mild, clean, slightly sweet smell. Off-odors include:

     • Sour: Lactic acid from bacterial growth.

     • Rancid: Fat breakdown (lipolysis).

     • Feed-like: Strong silage or garlic notes from cow diet.

     • Metallic: From equipment or oxidation.

3. Taste:

   • Should be clean, slightly sweet, and bland. Defects include:

     • Bitter: From proteolysis or late-lactation milk.

     • Salty: High mineral content or mastitis in the herd.

     • Cooked: Overheating during pasteurization.

   • Tasters sip small amounts, often at 15–20°C, to detect subtle flaws.

4. Scoring:

   • In contests, milk might be scored out of 100, with points deducted for defects (e.g., -5 for slight sourness, -10 for strong rancidity). The American Dairy Science Association has detailed scorecards for this.

Grading Milk (Formal Classification)

Grading is a systematic process to categorize milk for commercial use, based on safety and quality standards. In the U.S., the USDA and the Pasteurized Milk Ordinance (PMO) set the framework.

1. Grades:

   • Grade A: Highest quality, used for fluid milk (drinking). Strict bacterial and somatic cell count (SCC) limits:

     • Bacteria: <100,000 CFU/mL (raw), <20,000 CFU/mL (pasteurized).

     • SCC: <750,000/mL (indicates udder health; lower is better).

     • Must be cooled to <7°C within 2 hours of milking.

   • Grade B: Lower standard, typically for manufacturing (cheese, butter). Higher bacterial/SCC limits allowed (e.g., <1,000,000 CFU/mL).

   • Ungraded milk isn’t sold commercially—it’s rejected or diverted.

2. Testing Parameters:

   • Bacterial Count: Plate counts or rapid tests (e.g., Petrifilm) measure microbial load.

   • Somatic Cell Count: High SCC signals mastitis or cow health issues, affecting flavor and shelf life.

   • Solids Content: Fat and non-fat solids (SNF) are checked via infrared analyzers or Babcock tests. Minimums (e.g., 3.25% fat, 8.25% SNF) ensure richness.

   • Adulteration: Tests for added water (freezing point depression) or antibiotics (e.g., Delvotest).

   • Temperature: Raw milk must stay cold to slow bacterial growth.

3. Inspection:

   • Farms, equipment, and storage are checked for sanitation. Milk haulers and plants also follow protocols.

   • Samples are taken at the farm, tanker, or plant and sent to labs.

4. Regulatory Compliance:

   • Milk failing Grade A specs (e.g., antibiotics detected) is rejected outright. Farmers may face penalties or suspension.

Tools and Techniques

• Sensory: Trained inspectors or judges use their senses, often blind, to avoid bias.

• Lab Tests: Automated analyzers (e.g., Foss MilkoScan) measure fat, protein, and lactose in seconds.

• Microbial Kits: Swabs or dipslides check equipment cleanliness pre-milking.

• Thermometers/Data Loggers: Ensure proper cooling.

Practical Impact

• Producers: High grades mean better prices. Poor quality risks rejection or lower-value use (e.g., powder).

• Consumers: Grading ensures safety and consistency—Grade A milk is what you’ll find in stores.

• Processors: Quality affects yield (e.g., cheese-making) and shelf life.