Manufacturing of Market Milk

Manufacturing of Market Milk

Term ‘market milk’ refers to fluid whole milk that is sold to individuals usually for direct consumption. It excludes milk consumed on the farm and that used for the manufacture of dairy products.

The manufacturing of market milk involves a series of processes designed to transform raw milk into safe, standardized, and shelf-stable products suitable for direct consumer use. These processes ensure microbial safety, nutritional consistency, and sensory appeal while adhering to regulatory standards, such as those set by the Food Safety and Standards Authority of India (FSSAI) in India or equivalent bodies globally. Below is a detailed discussion of the steps, technologies, and considerations involved in manufacturing market milk.

Overview

• Definition: Market milk is processed liquid milk (e.g., pasteurized, toned, skimmed) packaged for retail sale.

• Objective: Ensure safety (pathogen-free), quality (standardized fat/SNF), and shelf life (days to months).

• Variants: Full cream, toned, double-toned, standardized, skimmed, flavored, fortified, etc.

Steps in Manufacturing Market Milk

1. Milk Buying & Collection

• Source: Raw milk from dairy farms (cow, buffalo, goat, etc.).

Buying

     Payment according to weight or volume (flat rate)

     Payment according to the fat content of milk

     Payment according to the use made of milk

     Payment of Premiums

     Payment according to the cost of production

Collection

  By Co-operative organization

  By Contractors

  By Individual Producers

‘milk – shed’ is the geographical area from which a city dairy receives its fluid milk supply.

• Process:

  • Collected in sanitized cans or via automated milking systems into bulk tanks.

  • Tested for quality: fat, SNF, microbial load (TBC <100,000 CFU/mL), somatic cell count (SCC <750,000/mL), adulterants, and antibiotic residues.

• Cooling: Immediately chilled to <4°C to prevent microbial growth.

Done on the farm or at the chilling centre. Optimum temperature range for the growth of common milk microorganisms is 20 to 400C.

Effect of storage tamp on bacterial growth in milk:

            Milk held for 18 hrs.                           Bacterial growth

            at tamp (0C)                                                    factor ( * )

                        0                                                          1.00

                        5                                                          1.05

                        10                                                        1.80   

                        15                                                        10.00 

                        20                                                        200.00

                        25                                                      1,20,000.00

Multiply initial count with this factor to get final count.

Cooling Methods

• In-can or Can-immersion method

• Surface cooler

• In-tank or Bulk-tank cooler

• Milk chilling centers

• Transport: Moved in refrigerated trucks to processing plants.

2. Reception and Storage

• Reception:

Milk Reception operations: weighing, sampling, testing, grading, unloading

Bacteriological standards of raw milk

            CFU/ ml (or gm) Grade

             < 105 Very Good    

            105    -   2x105 Good

            5x105  -  2x106 Fair

             > 2x106 Poor

Pasteurized Milk  < 30,000

• • Milk is weighed, filtered (to remove debris), and sampled for quality at the plant.

  • Organoleptic check: Odor, color, consistency.

• Storage: Held in insulated silos at <4°C; agitated to prevent fat separation.

3. Pre-Processing Adjustments

• Standardization:

  • Fat and SNF adjusted to meet variant specifications (e.g., 3.0% fat, 8.5% SNF for toned milk).

  • Cream separators (centrifuges) remove excess fat; skim milk or water added as needed.

• Clarification: Centrifugal clarifiers remove fine particles (e.g., somatic cells, dirt).

• Filtration: Additional filters ensure purity.

4. Heat Treatment

Heat treatment is critical for safety and shelf life. Options vary by market milk type:

Pasteurization: 

Louis pasteure – given heat treatment for preservation of wine at 122-1400f (50-600C).

Pasteurization of milk was first attributed to doctor Sozhlet of Zermony in 1886.

Definition – Pasteurization refers to the process of heating every particle of milk to at least 630C (1450F) for 30 minutes, or 720C (1610f)  for 15 seconds (or to any temperature time combination which is equally efficient ), in approve and proper operated equipment. after pasteurization milk is immediately cooled to 50C (410f) or below.

Objectives / purpose of Pasteurization

• Destruction of cent percent pathogenic microorganisms i.e. ensure safe for consumption.

• Improve keeping quality i.e. destruction of almost all spoilage organisms (85-99%)

Objections/Limitations of Pasteurization

• Significantly reduces nutritive value of milk.

• Pasteurized milk does not clot with rennet.

• It fails to destroy bacterial toxins in milk.

• In India pasteurization is not necessary as milk is invariably boiled on receipt by consumer.

Process of Pasteurization

1. • • Batch (LTLT): 63°C for 30 minutes.

     • High-Temperature Short-Time (HTST): 72°C for 15 seconds.

Equipment used in Pasteurization

 Plate heat exchangers (PHE) for HTST; vats for batch.

Outcome of Pasteurization

Kills vegetative pathogens (Listeria, Salmonella), reduces spoilage bacteria; phosphatase test negative.

Shelf Life of Pasteurized Milk

2-15 days refrigerated.

Formulation of standards for Pasteurization

Consideration involved in formulation of standards for pasteurization.

1.Bacterial destruction

Complete destruction of pathogens. Mycobacterium tuberculosis being considered the most heat resistant among pathogens is chosen as index organism for pasteurization. Any heat treatment (i.e. time- temperature combination), which killed T.B. germs, also destroy all other pathogens present in milk. 

2. Creamline reduction

The cream line or cream volume is reduced progressively with increase in the temperature- time of heating

3. Phosphatase inactivation

Complete destruction of enzyme phosphatase. Pasteurization is carried out at a heat-treatment temperature above that for phosphates in activation and yet below that for cream line reduction

Pasteurization requirements

             Particulars                     30 minute        15 seconds

Kill TB germs                           1380F/58.90C        1580F/700C

Inactivate phosphatase           1420F/61.10C        1600F/71.10C

Pasteurization requirements 1430F/61.70C        1610F/71.70C

Cream line reduction               1440F/62.20C        1620F/72.30C

Nutritive valve of HTST Pasteurized milk

• Vit C content of cow’s milk – 2 mg/100 ml. Losses of vitC – 70%.

• Other heat labile vits– vit B12, B1 (thiamin) vit B12 is heat stable to some extent, it is affected by pasteurization and destroyed by sterilization

• The biological value of milk proteins and vitamins are only slightly lowered down on pasteurization.

Losses in boiling of milk

• Losses of heat labile components.

• By formation of milk stone.

• Losses in the skin or deposit may amount to a loss of 14 percent for Ca & protein and 20 percent for fat.

Photochemical reaction

        Tropical conditions

Vit.C------oxidation-----> dehydroascorbic acid (unstable to heat)

          Riboflavin (sensitizer)  Losses on pasteurization

Advantages of HTST & Disadvantages of HTST

Advantages 

• Capacity can be increased.

• Equipment can be cleaned easily.

• Thermophils can not grow.

• Automatically controlled.

• Less time consuming.

• Quality is better than Batch pasteurization.

• Low initial cost.

• Low operating cost.

• Economical due to Regeneration Heating and Cooling.

• Space requirement is less.

 Disadvantages 

• Small quantity can not be handled.

• Complete destruction is not possible.

• Post pasteurization contamination is possible.

• Formation of milk stones.

Pasteurization efficiency

Alkaline phosphatase plays an important role in the energy transfer mechanism of the living beings.

APase activity in buffalo milk is lower than the cow milk (almost half)

38-40% AP – concentrated in cream where it is absorbed on the fat globules, remaining – distributed through out the milk in the lipoprotein particles.

Enzyme Alkaline phosphatase activity

Goat < buffalo< cow< ewe

pH for optimum activity of AP –  10

Thermal death point of Mycobacterium tuberculosis and pasteurization coincides with each other hence the activity of the enzymes serve as an indicator for the presence of the bacteria in the milk. 

Alkaline Phosphatase Test or Phosphate Test: Principle is based on determination of alkaline phosphatase activity in milk. Alkaline phosphatase enzyme is naturally present in milk. In Pasteurized milk it shall be absent since Time-Temperature combination for pasteurization is above than the Time-Temperature combination for inactivation of enzyme Alkaline phosphatase.  If, enzyme is present it cleaves a phosphate group  (mono-phosphoric ester bond) from the substrate, disodium phenyl phosphate, liberating phenol which then reacts with a color producing compound 2,6 dichloro-quinone compound (2,6 DCQC) to give a blue color.  The more enzyme activity present the more phenol is liberated giving a deeper color blue.  The intensity of the blue is then read visually or with a spectrophotometer. 

Milk is incubated with the DSPP and then indicator reagent is added. Blue colour indicates improper pasteurization

DSPP ---- alkaline phophatase------>free phenol

(phenol phosphoric                          +---->indophenol(blue colour)

acid compound)                            2,6 DCQC

                                     (organic compound indicator reagent)

Results of this procedure are expressed as micrograms of phenol per mL of milk.  A value of greater than 1 microgram is indicative of improper pasteurization. 

Ultra-High Temperature (UHT):

1. • Process: 135-150°C for 2-5 seconds via direct steam injection or indirect heating.

   • Outcome: Sterilizes milk, kills spores (Bacillus); shelf-stable for 3-6 months without refrigeration.

   • Shelf Life: Months (unopened).

Sterilization:

1. • Process: >100°C (e.g., 121°C for 15-20 minutes) in sealed cans/bottles post-packaging.

   • Outcome: Complete sterility; shelf-stable for >6 months.

   • Shelf Life: Long-term but less common today.

Differences in HTST, UHT and Sterilization of Milk

HTST (High-Temperature Short Time Pasteurization)

• Flow Type: Continuous.

• System: Plate heat exchanger (or tubular).

• Milk Path:

  • Pre-heated.

  • Heated to 72°C.

  • Held for 15 seconds in a holding tube (precise control of flow rate is critical).

  • Cooled immediately.

• Flow Control:

  • Use of a flow diversion valve to prevent under-processed milk from reaching the final product tank.

  • Laminar/turbulent flow depending on system design.

Designed to kill pathogens while maintaining flavor and nutritional quality.
Milk must be kept refrigerated.

UHT (Ultra-High Temperature)

• Flow Type: Continuous, faster flow.

• System: Tubular heat exchangers, steam injection, or steam infusion.

• Milk Path:

  • Preheated.

  • Instantaneously heated to 135–150°C.

  • Held for 2–5 seconds.

  • Rapidly cooled.

  • Aseptic packaging.

• Flow Control:

  • Often single-pass (no recycling like HTST).

  • Very high flow rates to minimize exposure time.

Achieves commercial sterility. 

Milk is shelf-stable, no refrigeration needed before opening.

Sterilization (In-bottle / Batch Sterilization)

• Flow Type: No flow (this is a batch process).

• System: Milk is filled into sealed containers (e.g., bottles or cans), then heated.

• Milk Path:

  • Milk is filled into final containers.

  • Containers are sealed.

  • Heated to 110–120°C for 10–30 minutes (in an autoclave or retort).

  • Cooled down gradually.

• Flow Control:

  • No continuous flow — it's static heating.

  • Longer time compensates for lower temperature.

Kills all microorganisms and spores.
Used for products with very long shelf life, like evaporated or condensed milk.

5. Homogenization

• Process: Milk is forced through small nozzles at high pressure (15-25 MPa), breaking fat globules into smaller sizes (<1 µm).

• Equipment: Homogenizers (single- or two-stage).

• Purpose:

  • Prevents cream separation.

  • Improves texture (smooth, creamy).

  • Enhances whiteness and stability.

• When: Typically post-pasteurization, pre-packaging; skipped for some traditional markets.

Steps in Milk Homogenization:

1. Preheat the Milk

• Temperature: Typically 55°C to 70°C (131°F to 158°F)

• Preheating reduces milk viscosity and prevents clogging of the homogenizer.

  1. 1. • At the time of  homogenization, milk temp should be above the MP of fat I.e. > 330C This is because fat should be in the liquid state fat should be in the liquid state for proper subdivision. The enzyme lipase should be inactivated, preferably prior to homogenization or immediately afterwards. This can be achieved by heating milk to a temp of 550C or above.

        • In routine practice milk is heated to 65-700C for homogenization on. Danger be avoided during or after homogenization.

2. Pass the Milk Through a Homogenizer

• A homogenizer has pistons and a homogenizing valve.

• Milk is pumped at high pressure (usually 100–250 bar or 1500–3600 psi) through a tiny opening.

3. Pressure Stages

Usually a two-stage homogenization:

1st stage (higher pressure): Breaks fat globules into small particles.

• • 1. 1. • If fat content is < 6 percent, single stage homogenization( 2000 – 2500 psi) is used.

          • higher pressure may increase the susceptibility of milk to curdle on heating.

2nd stage (lower pressure): Prevents re-clumping (agglomeration) of the fat droplets.

• • 1. 1. • if fat content is > 6 per cent

          • Two – stage homogenization is required to prevent fat clumping.

          • Ist stage   2000psi

          • IInd stage 500 psi

          • 1psi = 0.07 kg /cm²

4. Cool the Milk Immediately

• Rapid cooling to 4°C (39°F) prevents microbial growth and stabilizes the emulsion.

Homogenizer placement

• between regeneration heating and final heating section –best placement

• between final heating and holding section

• between FDV and regeneration cooling

• before regeneration heating

Possible sequences of various process

• clarification – Pre-heating – homogenization – pasteurization – cooling

• clarification – Pre heating – pasteurization – homogenization – cooling

• Pre- heating – Homogenization – clarification – pasteurization – cooling**

• Pre- heating – clarification - Homogenization – pasteurization – cooling

• Pre- heating – clarification – pasteurization – homogenization – cooling

(**Recommended under Indian condition ) main consideration

Main considerations involved in homogenization 

• Milk should be pasteurization prior or after homogenization

• Milk should be clarified after homogenization

Merits of homogenization

• No formation of cream layer.

• Fat in milk does not churn due to rough handling or excessive agitation

• More palatable due perhaps to brighter appearance heavier body and richer flavor.

• Produces soft curd and is better digested.

• Less susceptible to oxidized flavor development.

Homogenization efficiency 

Homogenization index : A sample of milk is stored in a graduated measuring glass for 48 hours at a temperature of 4-6 0C. The top layer (1/10 of the volume) is siphoned off, the remaining volume (9/10) is thoroughly mixed, and the fat content of each fraction is then determined. The difference in fat content between the top and bottom layers, expressed as a percentage of the top layer, is referred to as the homogenization index. The index for homogenised milk should be in the range of 1 to 10.

Homogenization Index (%) = (Top Fat % - Bottom Fat %) / Top Fat % × 100

Where:

• Top Fat = Fat content (%) in the top layer of milk after standing for a specific period (e.g., 48 hours at 4°C)

• Bottom Fat = Fat content (%) in the bottom layer

Interpretation:

• A low Homogenization Index (0-10) indicates efficient homogenization—fat is evenly distributed and not separating.

• A high Homogenization Index (> 10 ) indicates poor homogenization—fat is separating and rising to the top.

 Farrall index

The Farrall Index is a microscopic method for determining homogenization efficiency, based on the number of fat droplets having a diameter of > 2 µ over a standard field of 100 µ scare.  A Farrall index ranging from 5 to 7 implies “excellent” homogenization efficiency. Index exceeding 10 indicates inefficient homogenization. i.e. 90% of the fat globules shall have average diameter ≤ 2μ.

6. Fortification (Optional)

• Process: Addition of vitamins (e.g., A: 200-250 IU/100 mL, D: 40-100 IU/100 mL) or minerals (e.g., calcium).

• Method: Blended into milk post-heat treatment using premixes.

• Purpose: Addresses deficiencies (e.g., vitamin D in India); mandatory in some regions (e.g., U.S.).

7. Flavoring (Optional)

• Process: Addition of flavors (e.g., chocolate, strawberry) and sweeteners post-pasteurization.

• Standards: Must meet FSSAI additive limits; often UHT-treated for stability.

• Purpose: Targets children, niche markets.

8. Packaging

• Materials:

  • Plastic pouches (LDPE, common in India).

  • Tetra Paks (UHT milk, multilayer aseptic cartons).

  • Glass/plastic bottles (premium markets).

• Process:

  • Pasteurized: Filled in sanitized conditions, sealed, refrigerated.

  • UHT/Sterilized: Aseptically packed in sterile environments.

• Labeling: Fat/SNF content, processing type, expiry, nutritional info (per FSSAI).

9. Quality Control

• Tests:

  • Microbial: TBC (<20,000 CFU/mL post-pasteurization), coliforms (<10 CFU/mL), pathogens (absent).

  • Chemical: Fat/SNF compliance, no adulterants.

  • Physical: Taste, odor, color, no clots.

• Standards: FSSAI (India), Codex Alimentarius (global).

10. Distribution

• Cold Chain: Pasteurized milk kept at <4°C during transport and retail.

• Ambient: UHT/sterilized milk stored at room temperature.

• Shelf Life Monitoring: Expiry dates enforced (e.g., 2-3 days for pasteurized in India, 90 days for UHT).

Manufacturing Workflow

1. Collection → Cooling → Transport

2. Reception → Storage → Filtration

3. Standardization → Clarification

4. Pasteurization/UHT/Sterilization

5. Homogenization → Fortification/Flavoring

6. Packaging → Quality Check

7. Distribution

Technologies Used

• Centrifuges: For separation (cream, skim milk) and clarification.

• Heat Exchangers: Plate/tubular for pasteurization/UHT.

• Homogenizers: High-pressure pumps for fat dispersion.

• Aseptic Fillers: For UHT packaging (e.g., Tetra Pak machines).

• Cooling Systems: Bulk tanks, chillers for rapid cooling.

Indian Context

• Standards (FSSAI):

  • Toned: 3.0% fat, 8.5% SNF.

  • Double-Toned: 1.5% fat, 9.0% SNF.

  • Standardized: 4.5% fat, 8.5% SNF.

  • Full Cream: 6.0% fat, 9.0% SNF (buffalo base).

• Processing: ~70% of market milk pasteurized; UHT growing (~10-15% share).

• Scale: Cooperatives (e.g., Amul) process ~20 million liters/day; private dairies expanding.

• Adulteration Control: FSSAI mandates testing for water, urea, detergents.

Factors Affecting Manufacturing

1. Raw Milk Quality:

   • High TBC/SCC requires extra processing; affects yield.

2. Equipment:

   • Modern plants ensure consistency; small units may lack precision.

3. Energy:

   • Heat treatment and cooling are energy-intensive.

4. Consumer Preference:

   • India favors toned milk; Western markets prefer skimmed.

5. Regulation:

   • Compliance with FSSAI/BIS standards drives process rigor.

Significance

1. Safety: Eliminates pathogens (Listeria, E. coli), ensuring public health.

2. Shelf Life: Pasteurization (days), UHT (months) meet market needs.

3. Nutrition: Standardized fat/SNF and fortification address dietary gaps.

4. Economy: Supports dairy industry growth (e.g., India’s USD 125 billion market in 2023).

5. Convenience: Packaged milk suits urban lifestyles.

Challenges

• Adulteration: Water, skim powder overuse detected in ~41% of Indian samples (FSSAI).

• Infrastructure: Cold chain gaps in rural areas cause spoilage.

• Cost: UHT/packaging equipment expensive for small producers.

• Consumer Awareness: Preference for raw milk in some regions despite risks.