Milk SNF & Total Solids

In milk quality analysis, Solids-Not-Fat (SNF) and Total Solids (TS) are critical parameters that reflect the milk’s nutritional content, processing potential, and authenticity. They help assess milk composition, detect adulteration, and determine its value for dairy products like cheese, yogurt, or powdered milk. Here’s a detailed explanation:

Definitions

1. Solids-Not-Fat (SNF):

   • What It Is: The portion of milk solids excluding fat, consisting of proteins, lactose, minerals (e.g., calcium, potassium), and minor constituents like vitamins.

   • Typical Range: 8.5-9.0% in cow’s milk (varies by breed, diet, lactation stage).

   • Formula:
     SNF (%) = Total Solids (%) - Fat (%).

2. Total Solids (TS):

   • What It Is: The entire non-water portion of milk, including fat, proteins, lactose, and minerals.

   • Typical Range: 12-13% in cow’s milk (e.g., 3.5% fat + 8.7% SNF ≈ 12.2%).

   • Formula:
     TS (%) = Fat (%) + SNF (%).

Measurement Methods

1. Total Solids (TS):

   • Gravimetric Method:

     • Weigh a milk sample (e.g., 5 g), dry it in an oven (100-105°C) until constant weight, and calculate the residue as TS.

     • Formula: TS (%) = (Dry weight / Wet weight) × 100.

     • Use: Lab standard, accurate but slow.

   • Infrared Analyzer:

     • Measures absorption of infrared light by fat, protein, and lactose; calculates TS.

     • Use: Rapid, common in modern dairies.

2. Solids-Not-Fat (SNF):

   • Direct Calculation:

     • Measure fat (e.g., Gerber or Babcock method) and TS, then: SNF = TS - Fat.

   • Lactometer 

Pour milk into the lactometer jar:

• Fill the cylinder at least 3/4 full with the milk sample.

Measure the temperature of the milk:

• Use a thermometer and note if it's above or below 27°C.

Place the lactometer into the milk:

• Let it float freely without touching the sides.

• The lactometer reading (LR) is taken at the lowest point of the meniscus (the curved surface of the milk).

Correct the lactometer reading for temperature:

• Use the correction factor:

  • Add 0.2 for each °C below 27°C

  • Subtract 0.2 for each °C above 27°C

• This gives the Corrected Lactometer Reading (CLR).

Calculate Specific Gravity:

Formula: 

2. • • • • Specific Gravity (SG)=(CLR/1000)+1

     • Use specific gravity (SG) and fat content in a formula (e.g., Richmond’s):
       SNF (%)=4CLR​+(0.25×Fat)+0.44

       • • TS (%)=Fat+SNF 

         • TS (%)=4CLR​+(1.25×Fat)+0.44 

Where:

CLR = Corrected Lactometer Reading (as explained earlier)

Fat = Fat % in milk (from Gerber method or butyrometer)

2. • Infrared Analyzer: Directly outputs SNF alongside fat and TS.

Factors Affecting SNF and TS

1. Breed:

   • Jersey: Higher fat (4.5-5%) and SNF (~9.0-9.5%), TS ~13.5-14.5%.

   • Holstein: Lower fat (3.5%) and SNF (~8.5%), TS ~12-12.5%.

2. Diet:

   • High-energy feed (e.g., grains) boosts fat and protein, increasing TS and SNF.

   • Poor nutrition lowers both.

3. Lactation Stage:

   • Early (colostrum): High protein, TS up to 16-20%.

   • Late: Lower fat and SNF, reducing TS.

4. Adulteration:

   • Water addition lowers TS and SNF (e.g., TS <11% suspicious).

   • Skimming (fat removal) reduces TS but increases SNF relative to volume.

5. Season:

   • Summer: Lower fat/SNF due to heat stress; winter often higher.

Importance in Milk Quality

1. Nutritional Value:

   • SNF provides protein, lactose, and minerals essential for human nutrition.

   • TS reflects overall richness.

2. Processing:

   • Cheese: Higher SNF (protein) improves yield.

   • Powdered Milk: Higher TS reduces drying costs.

   • Yogurt: SNF affects texture and firmness.

3. Economic Value:

   • Farmers paid based on TS or SNF + fat content in many systems.

4. Adulteration Detection:

   • Low SNF/TS suggests water addition; confirmed with freezing point.

   • High SNF with low fat suggests skimming.

Standards and Regulations

• U.S. (FDA):

  • No strict SNF/TS minimum for raw milk, but processed milk (e.g., 2%) must meet fat + SNF norms (e.g., TS ~10.5%).

• India (FSSAI):

  • Cow milk: Min. 8.5% SNF, 3.5% fat (TS ~12%).

  • Buffalo milk: Min. 9.0% SNF, 5.0% fat (TS ~14%).

• EU: Varies by product; raw milk typically 8.5-9% SNF, 12-13% TS.

Practical Example

• Scenario: Milk tests at 3.8% fat, TS 12.6%.

  • Calculation: SNF = 12.6 - 3.8 = 8.8%.

  • Interpretation: Normal cow’s milk, suitable for processing.

• Alternative: Fat 2.0%, TS 9.5%.

  • SNF = 9.5 - 2.0 = 7.5%.

  • Interpretation: Possible water addition; check SG/freezing point.