🎓 Dairy Engineering — Complete Exam Notes
FTRI 4229 · BAU Mymensingh · FE-20 · Compiled by Shakil
⚠️ HOW TO USE THESE NOTES
This is your ONLY study resource — everything is here. Follow the 2-Day Strategy section first to plan your time. Use the sidebar to jump between topics. All flowcharts, numericals, and exam answers are included.
📅 2-Day Exam Strategy START HERE
🎯 Your Goal: Maximum marks from Butter, Cheese, Condensed Milk, Yoghurt, Platform Tests, Milk Powder Math, Ice Cream numericals.
DAY 1 — Foundation + Core Products
Morning
Milk Basics, Cream Separation (formulas + 1 numerical) — 1.5 hrs
Late Morning
Platform Tests — ALL 7 tests: procedures, interpretation tables — 1.5 hrs
Afternoon
BUTTER — Full process, overrun/yield formulas, 3 numericals — 2 hrs
Evening
CHEESE (Cheddar process, C/F ratio, defects) — 1.5 hrs
Night
Practice drawing: Cream separator, HTST pasteurizer, Butter flowchart, Cheese flowchart — 1 hr
DAY 2 — Products + Numericals + Revision
Morning
CONDENSED MILK (both sweetened + evaporated, sugar ratio numericals) — 2 hrs
Late Morning
YOGHURT (flow diagram, bacteria, defects) + ICE CREAM mix calculation — 1.5 hrs
Afternoon
ALL Numericals — Solve every problem in this file — 2 hrs
Evening
Quick revision: Read all Quick Reference tables — 1 hr
Night
Answer strategy practice + last minute tips — 30 min
💡 Priority Order: Platform Tests > Butter > Condensed Milk > Yoghurt > Cheese > Cream > Pasteurization > Ice Cream > Homogenization
⚡ Quick Reference — All Critical Numbers
🥛 Milk Composition
Water 87.5% | Fat 3.5-4% | Protein 3.2-3.5% | Lactose 4.6-4.8% | SNF 8.5-9%
🔥 Pasteurization Temps
LTLT: 63°C / 30 min | HTST: 72°C / 15 sec | UHT: 135-150°C / 2-5 sec
🧈 Butter PFA Specs
Fat ≥80% | Moisture 16-18% | Curd ≤1.5% | Salt ≤3%
🧀 Cheese PFA Specs
Moisture ≤43% | Fat ≥42% of DM | C/F ratio 0.68-0.70
🥫 Condensed Milk (Sweetened)
Fat ≥9% | TMS ≥31% | Sugar ≥40% | Sugar Ratio 62.5-64.5%
🥫 Evaporated Milk
Fat ≥8% | TMS ≥26% | NO sugar added | Storage ≤7°C
🫙 Yoghurt
Heat: 90-95°C / 30-45 min | Incubation: 42°C / 3-4 hrs | Endpoint: pH 4.5-4.6
🔬 MBRT Quality Scale
≥5h=Very Good | 3-4h=Good | 1-2h=Fair | ≤0.5h=Poor
⚗️ Alcohol Test
68% ethanol | 5ml:5ml (1:1) | Positive=clots=heat-unstable=REJECT
🫙 Cream Separator
Bowl speed: 5000-6000 rpm | Milk fat density: 0.93 | Skim milk density: 1.036
🧈 Churning Temp
7-8°C | Cream fat: 35-40% | Ripening culture: S.lactis + S.diacetilactis + S.cremoris
⚙️ Homogenizer Pressure
Single stage: 1500-2000 psi | Two stage: 2000+500 psi | Temp: 55-65°C
🥛 Milk — Composition, Properties & Types ⭐⭐⭐
Composition of Cow Milk
| Component | % | Exam Note |
|---|---|---|
| Water | 87.5% | Most abundant component |
| Fat | 3.5–4.0% | Legal minimum varies by standard |
| Protein | 3.2–3.5% | Casein (80%) + Whey proteins (20%) |
| Lactose | 4.6–4.8% | Reducing sugar; involved in Maillard browning |
| Ash/Minerals | 0.7–0.8% | Ca, P, K, Na, Mg |
| SNF (Solids-Not-Fat) | 8.5–9.0% | SNF = Total Solids − Fat |
| Total Solids | 12.5–13.0% | TS = Fat + SNF |
Physico-Chemical Properties
| Property | Value |
|---|---|
| pH | 6.6–6.8 |
| Titratable Acidity | 0.13–0.17% lactic acid |
| Specific Gravity (at 15°C) | 1.028–1.032 |
| Freezing Point | −0.55°C (Used to detect water adulteration) |
| Boiling Point | 100.17°C |
| Refractive Index | 1.3440–1.3485 |
📝 Exam Formula — Fleischmann's Formula for Specific Gravity:
Richmond's Formula:
% Fat = (0.8865 × W) + 0.2525 — where W = water contentRichmond's Formula:
Total Solids = 1.2F + 2.665 × [100(D−1)/D]Types of Special Milk
| Type | Description |
|---|---|
| Toned Milk | 3% fat, 8.5% SNF (diluted whole milk + skim powder + water) |
| Double Toned Milk | 1.5% fat, 9% SNF |
| Standardized Milk | 4.5% fat, 8.5% SNF |
| Reconstituted Milk | Milk powder + water reconstituted to liquid |
| Recombined Milk | Butterfat + skim milk powder + water |
🫙 Cream & Cream Separation ⭐⭐⭐
Cream Classification (FSSR 2011)
| Type | Fat % | Key Note |
|---|---|---|
| Low Fat Cream | ≥25% | |
| Medium Fat Cream | ≥40% | |
| High Fat Cream | ≥60% | Cream without fat label = High Fat Cream |
Key Formulas — Must Memorize!
Formula 1 — SNF in Cream:
%SNF in Cream = [(100 − %Fat_cream) × %SNF_milk] / (100 − %Fat_milk)
%SNF in Cream = [(100 − %Fat_cream) × %SNF_milk] / (100 − %Fat_milk)
Formula 2 — Cream Acidity:
%TA_cream = (%Fat_milk / %Fat_cream) × %TA_milk
%TA_cream = (%Fat_milk / %Fat_cream) × %TA_milk
Principle of Cream Separation
Based on density difference between milk fat and skim milk:
• Milk fat density at 16°C: 0.93 g/cm³ (lighter)
• Skim milk density at 16°C: 1.036 g/cm³ (heavier)
Stoke's Law (Gravity): V ∝ r² × (ds−df) / η
Stoke's Law (Centrifugal): V ∝ N² (N = bowl speed in rpm) — MOST IMPORTANT
• Milk fat density at 16°C: 0.93 g/cm³ (lighter)
• Skim milk density at 16°C: 1.036 g/cm³ (heavier)
Stoke's Law (Gravity): V ∝ r² × (ds−df) / η
Stoke's Law (Centrifugal): V ∝ N² (N = bowl speed in rpm) — MOST IMPORTANT
Gravity vs Centrifugal — Comparison
| Feature | Gravity Method | Centrifugal Method |
|---|---|---|
| Speed | 12–24 hours | Minutes |
| Fat loss in skim milk | ≥0.2% | ≤0.1% |
| Equipment | Shallow pans | Bowl with stacked discs |
| Hygiene | Risk of contamination | Enclosed, hygienic |
| Status | Obsolete | Used universally ✅ |
Centrifugal Separator — Key Parts
- Discs (stacked): Increase separation surface area enormously
- Top disc (adjustable screw): Controls cream fat % — More cream opening = lower fat % cream
- Bowl spindle: Connects to drive; rotates at 5000–6000 rpm
- Inlet (60–70 rpm motor): Slow input speed, geared up to bowl speed
- Skim milk outlet: Exits from outer zone (heavy phase)
- Cream outlet: Exits from center (light phase)
⭐ Exam Note — Clumping: Maximum clumping occurs at 7°C. Buffalo milk creams faster than cow milk due to larger fat globules.
🔥 Pasteurization & Sterilization ⭐⭐⭐
Definition: Pasteurization is the process of heating every particle of milk to a specific temperature for a specific time and immediately cooling, to destroy pathogens without significantly altering the composition, flavor, or nutritive value.
| Method | Full Name | Temperature | Time |
|---|---|---|---|
| LTLT | Low Temp Long Time | 63°C (145°F) | 30 minutes |
| HTST | High Temp Short Time | 72°C (161°F) | 15 seconds |
| UHT | Ultra High Temperature | 135–150°C | 2–5 seconds |
| Sterilization (can) | In-can sterilization | 116–118°C | 15 minutes |
HTST Pasteurizer Components (Flow Order)
Balance Tank (Float valve controls flow)
↓
Centrifugal Pump
↓
Regenerator Section (Pre-heat using hot pasteurized milk — saves energy)
↓
Heater Section (Steam or hot water → 72°C)
↓
Holding Tube (15 seconds at 72°C — critical!)
↓
Flow Diversion Valve (FDV) — sends sub-standard milk back to balance tank
↓
Cooling Section (Chilled water → 4°C)
↓
Pasteurized Milk (4°C)
📝 Critical Control Points: Holding tube temperature must NEVER drop below 72°C. The FDV ensures this — if temp drops, milk is diverted back automatically.
⚙️ Homogenization ⭐⭐⭐
Definition: Process of breaking up fat globules in milk into smaller, uniform particles by forcing milk through a small orifice under high pressure, to prevent creaming.
Key Facts
- Purpose: Reduce fat globule size to <2 microns to prevent creaming
- Temperature: 55–65°C (optimal — fat in liquid state)
- Pressure (Single stage): 1500–2000 psi
- Pressure (Two stage): Stage 1: 2000 psi + Stage 2: 500 psi
- Effect: Whiter color, better flavor, softer curd, increased digestibility
- Disadvantage: Increases susceptibility to lipolysis (rancidity) if done cold
Applications
| Product | Pressure Used |
|---|---|
| Milk | 1500–2000 psi |
| Ice cream mix | 2000–2500 psi |
| Cream | 1000–1500 psi |
| Evaporated milk | 2000+500 psi (two-stage) |
🧈 Butter Technology ⭐⭐⭐ HIGH PRIORITY
Definition: Butter is the fatty product derived by churning cream or milk or cream and salt, with or without coloring matter.
PFA (1976) Specifications — Must Know!
| Component | Standard | Exam Tip |
|---|---|---|
| Milk Fat | ≥ 80% | Minimum — most important number |
| Moisture | ≤ 16% (salted) / ≤ 16% (unsalted) | Legal max = 16% |
| Curd | ≤ 1.5% | |
| Salt (NaCl) | ≤ 3% | Only for salted butter |
Classification of Butter
| Type | Description |
|---|---|
| Sweet/Fresh Cream Butter | From pasteurized, unripened cream — mild flavor |
| Ripened/Cultured Cream Butter | From ripened (fermented) cream — stronger flavor ⭐ |
| Salted Butter | Salt added (1–3%) for preservation and flavor |
| Unsalted/White Butter | No salt — used for cooking |
| Whey Butter | Made from cream recovered from whey |
Important Terms — Define These!
CHURNING: The mechanical agitation of cream to convert the fat from an emulsion of fat-in-water (cream) to an emulsion of water-in-fat (butter). Fat globule membranes are disrupted → fat globules aggregate → butter granules form.
RIPENING: Process of holding pasteurized cream at low temperature after inoculation with starter culture (S. lactis, S. diacetilactis, S. cremoris). Produces: lactic acid (↑flavor), diacetyl (aroma), CO₂. Temp: 8–10°C, Time: 6–15 hours.
WORKING: Process of kneading butter granules to expel buttermilk, produce uniform texture, incorporate salt, and blend added water and color into a homogeneous mass. Produces the final plastic, smooth texture.
Butter Manufacturing — Complete Flow Diagram
Receiving Milk
↓
Pre-heating (38–40°C)
↓
Neutralization (if needed, with Na₂CO₃ — bring acidity to 0.1%)
↓
Separation (Get cream at 35–40% fat)
↓
Standardization (adjust cream fat %)
↓
Pasteurization (90–95°C / 15 sec for cream)
↓
Cooling (7–8°C)
↓
Ripening — Optional (8–10°C, 6–15 hrs with starter culture)
↓
Aging (0–5°C, 2–8 hrs — crystallize fat)
↓
Churning (7–8°C — cream → butter + buttermilk)
↓
Washing (cold water removes buttermilk traces)
↓
Salting + Working (knead, expel water, add salt)
↓
Cooling (10–15°C before packaging)
↓
Packaging + Cold Storage (4°C or below)
Factors Influencing Churnability ⭐⭐⭐
| Factor | Optimum | Effect |
|---|---|---|
| Fat % in cream | 35–40% | Too low = slow churning; too high = sticky butter |
| Churning temperature | 7–8°C | Too high = soft butter; too low = hard to churn |
| Acidity of cream | 0.2–0.25% (sweet), 0.35% (ripened) | High acidity = faster but weaker butter |
| Pasteurization | Required | Ensures safety; affects flavor |
| Agitation speed | Moderate | Too fast = froth; too slow = no churning |
| Size of churn | Half full | Overloading reduces efficiency |
🔢 Butter Overrun & Yield — Formulas & Problems
Overrun % = [(Butter made (B) − Fat in churn (F)) / Fat in churn (F)] × 100
Yield (Y) = [F × (100 + %Overrun)] / 100
Problem 1: From 800 kg of fat, 1000 kg of butter is produced. Find overrun % and verify with yield formula.
Given: B = 1000 kg, F = 800 kg
%Overrun = [(1000 − 800) / 800] × 100 = (200/800) × 100 = 25%
Verify: Y = [800 × (100+25)] / 100 = [800 × 125] / 100 = 1000 kg ✓
Answer: Overrun = 25%
Problem 2: 500 kg cream (40% fat) yields 220 kg butter. Calculate overrun % and yield per kg fat.
Given: Cream = 500 kg, fat = 40%, Fat in churn = 500×0.40 = 200 kg. Butter = 220 kg
%Overrun = [(220 − 200) / 200] × 100 = (20/200) × 100 = 10%
Yield per kg fat = 220/200 = 1.1 kg butter per kg fat
Answer: Overrun = 10%
Defects of Butter ⭐⭐⭐
| Defect | Cause | Prevention |
|---|---|---|
| Rancid/Lipolytic | Lipase enzyme activity (fat hydrolysis) | Proper pasteurization; avoid agitation of cold milk |
| Oxidized/Tallowy/Cardboardy | Auto-oxidation of unsaturated fatty acids; copper contamination | Avoid copper equipment; antioxidants; proper packaging |
| Cheesy/Putrid | Bacterial proteolysis; poor quality cream | Proper pasteurization; good quality cream |
| Sour/Acid | Excess lactic acid from over-ripening | Control ripening time and temperature |
| Flat/Lacking flavor | Under-ripening; sweet cream butter | Adequate ripening |
| Feed taint | Cows fed strong-smelling feeds (onion, garlic, cabbage) | Avoid such feeds before milking |
| Yeasty/Fermented | Yeast contamination | Proper sanitation |
| Defect | Cause | Prevention |
|---|---|---|
| Soft/Oily body | High churning temp; high proportion of soft fats in diet; improper aging | Churn at 7-8°C; proper aging at low temp |
| Crumbly/Brittle | Low churning temp; high proportion of hard fats | Proper churning temp; adequate working |
| Gummy/Sticky | High churning temp; too little washing | Proper temp; adequate washing |
| Greasy | Too much working; high temp during working | Proper working conditions |
| Mealy/Granular | Too little working; inadequate salt mixing | Adequate working |
| Leaky/Weeping | Poor working; large water droplets not dispersed | Proper working; good emulsification |
| Defect | Cause | Prevention |
|---|---|---|
| Mottled | Uneven distribution of salt; uneven mixing of color | Proper salting; thorough working |
| Pale/White color | Winter/indoor-fed cows (low carotene in feed) | Add annatto color |
| Wavy/Streaked | Churning too fast or too early | Proper churning speed and temperature |
| Excessive yellow | Too much color added; summer milk with high carotene | Standardize color addition |
🧀 Cheese Technology ⭐⭐⭐ HIGH PRIORITY
Definition: Cheese is the fresh or ripened solid or semi-solid product obtained by coagulating milk, cream, skim milk, or their combination, with the aid of rennet or other coagulants, and draining the whey.
PFA (1976) Specifications
| Type | Moisture Max | Fat (of dry matter) Min |
|---|---|---|
| Hard Cheese (e.g., Cheddar) | ≤43% | ≥42% |
| Soft Cheese (e.g., Cottage) | ≤70% | ≥10% |
Classification of Cheese
| Basis | Types | Examples |
|---|---|---|
| Moisture content | Hard, Semi-hard, Soft | Cheddar | Gouda | Cottage |
| Type of milk | Cow, Goat, Buffalo, Mixed | Mozzarella (buffalo) | Brie (cow) |
| Ripening agent | Bacteria ripened, Mould ripened | Cheddar | Roquefort |
| Method of manufacture | Rennet coagulated, Acid coagulated | Cheddar | Cottage |
Scientific Basis of Cheese Making
RIPENING (SOURING): Lactic acid bacteria (starter culture) convert lactose → lactic acid → pH drops → casein destabilized → coagulation when rennet added.
Key pH values: Fresh milk = 6.6–6.8 | After souring = 5.8–6.2 | Isoelectric point of casein = 4.6 | Cheddar curd pressing pH ≈ 5.0–5.2
Key pH values: Fresh milk = 6.6–6.8 | After souring = 5.8–6.2 | Isoelectric point of casein = 4.6 | Cheddar curd pressing pH ≈ 5.0–5.2
Cheddar Cheese — Complete Flow Diagram ⭐⭐⭐
Receiving Milk (4.5% fat, 2.7% casein tested)
↓
Pre-heating (35–40°C)
↓
Filtration/Clarification
↓
Standardization (Casein/Fat ratio = 0.68–0.70)
↓
Pasteurization (72°C / 15 sec)
↓
Cooling to Setting Temp (30–32°C)
↓
Starter Addition (1–2% culture)
↓
Ripening (30 min at 30°C)
↓
Rennet Addition (coagulant — calf rennet or microbial)
↓
Coagulation (30–40 min → firm gel)
↓
Cutting Curd (1.5–2 cm cubes)
↓
Cooking/Scalding (38–40°C — expels whey)
↓
Pitching (settle curd at bottom)
↓
Drainage of Whey
↓
Cheddaring ← UNIQUE to Cheddar!
Stack & turn slabs every 15 min at 38°C until pH 5.2–5.4
Stack & turn slabs every 15 min at 38°C until pH 5.2–5.4
↓
Milling (cut into small pieces)
↓
Salting (2–3% salt)
↓
Hooping/Pressing (remove remaining whey)
↓
Drying (form rind)
↓
Ripening/Curing (4–10°C, 3–12 months for Cheddar)
↓
Finished Cheddar Cheese
⭐ CHEDDARING — Most Asked Exam Point: Cheddaring is the process UNIQUE to Cheddar cheese where the drained curd slabs are stacked and turned repeatedly at 38°C. This forms characteristic long parallel fibers (stringy texture) and acidifies the curd to pH 5.2–5.4 through continued bacterial action.
Cottage Cheese vs Cheddar — Key Differences
| Feature | Cheddar | Cottage Cheese |
|---|---|---|
| Milk used | Full fat or standardized | Skim milk |
| Coagulant | Rennet | Acid (lactic) ± small rennet |
| Cheddaring | Yes ✅ | No ❌ |
| Pressing | Yes ✅ | No ❌ |
| Ripening | Yes (3–12 months) | No ❌ (fresh) |
| Moisture | ≤43% | ~70% |
| Fat (DM) | ≥42% | Low |
Cheese Standardization — C/F Ratio Calculation ⭐⭐⭐
Target Casein/Fat (C/F) ratio = 0.68–0.70
If C/F too low (fat surplus) → Add skim milk
If C/F too high (fat deficit) → Add cream
If C/F too low (fat surplus) → Add skim milk
If C/F too high (fat deficit) → Add cream
Problem: Standardize 1000 kg milk (4.5% fat, 2.7% casein) to C/F = 0.70. Available skim milk: 2.8% casein, 0% fat.
Given: Milk fat = 4.5%, Casein = 2.7%, Target C/F = 0.70, SM casein = 2.8%
Fat in 1000 kg = (4.5/100) × 1000 = 45 kg
Required casein = 0.70 × 45 = 31.5 kg
Casein in milk = (2.7/100) × 1000 = 27 kg → Need 4.5 kg more casein
Let SM = kg of skim milk to add
27 + (2.8/100)×SM = 31.5
0.028×SM = 4.5
SM = 4.5/0.028 = 160.7 kg
27 + (2.8/100)×SM = 31.5
0.028×SM = 4.5
SM = 4.5/0.028 = 160.7 kg
Answer: Add 160.7 kg skim milk
Cheese Defects
| Category | Defect | Cause |
|---|---|---|
| Flavor | Bitter | Excess rennet; contaminating bacteria; over-ripe |
| Flavor | Rancid | Lipase action (molds, bacteria) |
| Flavor | Acid/Sharp | Too much starter; over-acidification |
| Body | Pasty/Soft | High moisture; under-pressed |
| Body | Crumbly | Too low fat; over-acidification |
| Body | Gassy/Open texture | Coliform contamination (CO₂ production) |
| Color | Pink/Red | Pigment-producing bacteria (Micrococcus) |
| Finish | Cracked rind | Too dry curing; poor bandaging |
Cheese Scoring System
| Factor | Max Marks |
|---|---|
| Flavor | 45 |
| Body & Texture | 30 |
| Finish & Appearance | 15 |
| Color | 10 |
| Total | 100 |
🥫 Condensed Milk Technology ⭐⭐⭐ HIGH PRIORITY
Definition & Classification
Condensed Milk: Products obtained by evaporating part of water from whole milk or fully/partly skimmed milk, with or without addition of sugar.
Key inventor: Gail Borden (USA, 1856) — "Father of milk condensing" — used evaporation under vacuum (in vacuo)
Key inventor: Gail Borden (USA, 1856) — "Father of milk condensing" — used evaporation under vacuum (in vacuo)
PFA Specifications (1976) — MUST MEMORIZE
| Type | Fat | TMS | Sugar | Preservation |
|---|---|---|---|---|
| Sweetened Condensed Milk | ≥9% | ≥31% | ≥40% | Sugar (osmotic) |
| Evaporated Milk (Unsweetened) | ≥8% | ≥26% | None | Heat sterilization |
| Sweetened Condensed Skim | ≤0.5% | ≥26% | ≥40% | Sugar |
| Unsweetened Condensed Skim | ≤0.5% | ≥20% | None | Heat sterilization |
⭐ Critical Difference: Sweetened Condensed Milk is preserved by HIGH SUGAR concentration (osmotic effect). Evaporated Milk is preserved by HEAT STERILIZATION (116–118°C, 15 min).
Sweetened Condensed Milk — Flow Diagram ⭐⭐⭐
Receiving Milk (≤10°C, no antibiotics, no abnormal milk)
↓
Alcohol test + COB test at reception!
Filtration/Clarification (33–40°C)
↓
Standardization (Fat:SNF ratio = 1:2.44)
↓
Forewarming/Pre-heating (115–118°C, No Hold — Flash method)
Purpose: Kill microorganisms, control viscosity, prevent age-thickening
↓
Condensing in Vacuum Pan (2.5:1 ratio, ~55–60°C under vacuum)
Heart of the condensery! Remove water at low temp to prevent damage
↓
Sugar Addition — at END of condensing (sucrose dissolved in water, filtered)
Add at end! NOT before — would increase viscosity and microbial heat resistance
↓
Homogenization (Optional)
↓
Cooling & Crystallization (Controlled — to get lactose crystals <16 microns)
Seeding with fine lactose crystals ensures smooth texture
↓
Packaging (airtight cans) + Storage (≤10°C, humidity <50%)
Evaporated Milk — Flow Diagram
Receiving Milk → Filtration → Standardization
↓
Forewarming (115–118°C, No Hold)
↓
Evaporation (Vacuum, 2.5:1 ratio)
↓
Homogenization (49°C, Two-stage: 2000+500 psi) ← KEY STEP
Prevents fat separation during long storage
↓
Cooling (7°C)
↓
Pilot Sterilization Test (determine stabilizer — Na citrate or Na phosphate)
↓
Packaging (sealed cans)
↓
Sterilization (116–118°C / 15 min, revolving reel)
↓
Cooling (27–32°C) + Shaking (prevent gel)
↓
Storage (≤7°C)
Vacuum Pan — 5 Major Parts ⭐⭐⭐
| Part | Function |
|---|---|
| 1. Heating Surface | Steam coils/jacket/tubes — evaporates water from milk |
| 2. Vapour Space | Above milk level — water vapour collects here; has thermometer, vacuum gauge |
| 3. Entrainment Separator | Reclaims milk particles dragged by vapour — prevents milk solid losses |
| 4. Condenser | Condenses water vapour using cooling water (~20 kg water per 1 kg vapour) |
| 5. Vacuum Pump / Steam Ejector | Maintains partial vacuum so water boils at low temperature (~55°C) |
🔢 Sugar Ratio Calculation ⭐⭐⭐
Formula I: %SR = [% sugar / (100 − %TMS)] × 100
Formula II: %SR = [% sugar / (% sugar + % water)] × 100
Optimum Sugar Ratio = 62.5 – 64.5%
Formula II: %SR = [% sugar / (% sugar + % water)] × 100
Optimum Sugar Ratio = 62.5 – 64.5%
Problem 1: Condensed milk contains 31% TMS and 43.1% added sugar. Calculate Sugar Ratio.
%SR = [43.1 / (100 − 31)] × 100
%SR = [43.1 / 69] × 100 = 0.6246 × 100
Answer: Sugar Ratio = 62.5% ✓ (within optimum range)
Problem 2: Find % sugar needed in condensed milk if TMS = 28% and target SR = 64%.
% sugar = [(100 − %TMS) × SR] / 100
% sugar = [(100 − 28) × 64] / 100 = [72 × 64] / 100 = 4608 / 100
Answer: % sugar = 46.08%
🔢 Standardization Numerical — Condensed Milk
Problem 3: 10,000 kg milk (3.60% fat, 8.9% SNF) needs to give condensed milk with 9.05% fat, 31% TMS. Available cream: 40% fat. Find cream to add.
SNF in cream = [(100−40)×8.9]/(100−3.60) = (60×8.9)/96.4 = 534/96.4 = 5.54%
Check ratios: In milk: SNF/Fat = 8.9/3.60 = 2.47 | In condensed: SNF/Fat = (31−9.05)/9.05 = 21.95/9.05 = 2.43 → 2.47 > 2.43 → fat deficit → add cream
Let C = cream (kg) to add:
Fat balance: 360 + 0.4C (kg fat total)
SNF balance: 890 + 0.0554C (kg SNF total)
Ratio: (890 + 0.0554C) / (360 + 0.4C) = 2.43
Fat balance: 360 + 0.4C (kg fat total)
SNF balance: 890 + 0.0554C (kg SNF total)
Ratio: (890 + 0.0554C) / (360 + 0.4C) = 2.43
890 + 0.0554C = 874.8 + 0.972C → 15.2 = 0.9166C → C = 16.6 kg
Answer: Add 16.6 kg cream
Defects of Condensed & Evaporated Milk
| Defect | Cause | Prevention |
|---|---|---|
| Sandiness (lactose crystals) | Incorrect cooling/crystallization | Controlled cooling; seeding with fine crystals |
| Age-thickening | Excessive forewarming; high storage temp | Optimal forewarming; store ≤10°C |
| Mould buttons | Aspergillus repens; oxygen in can | Vacuum packaging; store ≤10°C |
| Browning (Maillard) | Amino acid + lactose + heat → melanoidins | Optimal heat treatment; store cool |
| Bloats | Yeast (Torula) contamination | Good sanitation; hermetic seal |
| Fat separation (evap.) | Inadequate homogenization | Two-stage homogenization (2000+500 psi) |
| Cooked flavor | High sterilization heat | UHT + aseptic packaging |
| Feathering in coffee | Excessively high viscosity | Control viscosity |
🫙 Yoghurt Technology ⭐⭐⭐ HIGH PRIORITY
Definition: Yoghurt is an acidified, coagulated product obtained from milk (or concentrated/reconstituted milk) by fermentation with specific lactic acid-producing bacteria, resulting in a reduction of pH and coagulation of proteins.
Composition
| Component | Amount |
|---|---|
| Protein | 5–7% |
| Fat | 0–5% (low fat <3%, non-fat <0.5%) |
| Carbohydrate | 7.8% |
| MSNF (target) | 12% (natural milk = 8.5% → increase with SMP) |
| Total Solids | 9–20% |
Bacteria Used ⭐⭐⭐
Primary (must know):
• Lactobacillus bulgaricus — produces lactic acid, acetaldehyde (aroma)
• Streptococcus thermophilus — produces lactic acid, CO₂
• These two work SYMBIOTICALLY — each helps the other grow
Other strains used:
• Lactobacillus acidophilus (probiotic)
• Streptococcus diacetylactis (diacetyl flavor)
• Yeasts: Saccharomyces lactis (in kefir)
• Lactobacillus bulgaricus — produces lactic acid, acetaldehyde (aroma)
• Streptococcus thermophilus — produces lactic acid, CO₂
• These two work SYMBIOTICALLY — each helps the other grow
Other strains used:
• Lactobacillus acidophilus (probiotic)
• Streptococcus diacetylactis (diacetyl flavor)
• Yeasts: Saccharomyces lactis (in kefir)
Types of Yoghurt
| Type | Key Feature |
|---|---|
| Set Yoghurt | Inoculated, packed in cups, then incubated → gel forms in container |
| Stirred Yoghurt | Fermented in large vat, then stirred to break gel → poured into cups |
| Fluid/Drinkable Yoghurt | More water, low viscosity — pourable |
| Frozen Yoghurt | Frozen like ice cream — dessert form |
| Thermized Yoghurt | Heat-treated after fermentation — extended shelf life |
Set Yoghurt — Manufacturing Flow Diagram ⭐⭐⭐
Receiving Milk
↓
Fat Standardization (target: 0%–3.2%+ depending on type)
↓
Protein Standardization — Add Skim Milk Powder (SMP)
Target: MSNF from 8.5% → 12% | Purpose: Improve firmness, reduce syneresis
Target: MSNF from 8.5% → 12% | Purpose: Improve firmness, reduce syneresis
↓
Complete Mixing (NO air incorporation!)
↓
Heat Treatment (90–95°C for 30–45 min)
Destroys organisms + denatures whey proteins → better gel strength
Destroys organisms + denatures whey proteins → better gel strength
↓
Homogenization — Optional (2000+500 psi)
↓
Cooling to Fermentation Temperature (42–45°C)
↓
Inoculation with Culture (2–3% yoghurt starter)
↓
Packing (into 150–250 ml cups/sachets) ← Done BEFORE incubation for Set type
↓
Incubation (42°C for 3–4 hours, undisturbed!)
Lactose → Lactic acid | pH drops 6.6 → 4.5–4.6 | Casein coagulates at pH 4.6
Lactose → Lactic acid | pH drops 6.6 → 4.5–4.6 | Casein coagulates at pH 4.6
↓
Rapid Cooling to 4–5°C (stops fermentation — prevents over-acidification)
↓
Cold Storage (4°C) → Sale within 21–28 days
📝 Key Difference — Set vs Stirred: In SET yoghurt, cups are filled BEFORE incubation → gel forms in cup. In STIRRED yoghurt, fermentation occurs in a large tank → gel is broken by stirring → then filled into cups. Set = firmer gel. Stirred = smooth, creamy.
SMP Addition Calculation ⭐⭐⭐
SMP required (kg) = M × (Pt − Pm) / (Ps − Pt)
Where: M = milk (kg), Pt = target protein %, Pm = milk protein %, Ps = SMP protein % (~36%)
Where: M = milk (kg), Pt = target protein %, Pm = milk protein %, Ps = SMP protein % (~36%)
Problem: Standardize 500 kg milk (3.0% protein) to 5.0% protein using SMP (36% protein).
SMP = M × (Pt − Pm) / (Ps − Pt)
SMP = 500 × (5.0 − 3.0) / (36 − 5.0) = 500 × 2.0 / 31.0 = 1000/31
Answer: SMP = 32.26 kg
Defects of Yoghurt ⭐⭐⭐
| Defect | Cause | Prevention |
|---|---|---|
| Syneresis (whey off) | Low protein; inadequate heat treatment; vibration during incubation | Increase MSNF; proper heat treat; undisturbed incubation |
| Weak body/gel | Low protein, short incubation, too little culture | Add SMP; adequate incubation; proper culture % |
| Over-acid taste | Over-fermentation; slow cooling; high incubation temp | Monitor pH; rapid cooling to 4°C |
| Flat/bland flavor | Poor culture; under-incubation; inhibitors in milk | Active culture; proper time; inhibitor test |
| Contamination/yeast | Poor sanitation; post-contamination | GMP; aseptic packing |
| Lumpy/grainy | SMP not fully dissolved; poor mixing | Complete dissolution; proper mixing |
BSTI Standard for Yoghurt (Bangladesh)
Standard: BDS CAC-A-11(a) 2002
Key requirements on label: Date of manufacture, Date of packaging, Sell-by date, Best-before date, Use-by date (expiration), Ingredients list, Barcode
Key requirements on label: Date of manufacture, Date of packaging, Sell-by date, Best-before date, Use-by date (expiration), Ingredients list, Barcode
🍦 Ice Cream — Technology & Numericals ⭐⭐⭐
Ice Cream Mix Composition (Standard)
| Component | Typical % |
|---|---|
| Fat (milk fat) | 10–14% |
| Serum Solids / MSNF | 9–12% |
| Sugar (sucrose) | 13–16% |
| Stabilizer (gelatin/CMC) | 0.2–0.5% |
| Emulsifier (mono/diglycerides) | 0.1–0.2% |
| Water | ~60–65% |
🔢 Ice Cream Mix Formulation — Solved Problem ⭐⭐⭐
Problem 1: Formulate 100 kg ice cream mix with: Fat 10%, Serum solids 11%, Sugar 14.5%, Stabilizer 0.3%. Available: Whole milk (3.5% fat, 8.5% SNF), Cream (35% fat, 5.6% SNF), SMP (36% protein = ~96% milk solids). Find amounts of whole milk (X), cream (Y), and SMP (Z).
Set up 3 equations from fat, serum solids, and total mass:
Fat: 0.035X + 0.35Y = 10 kg
SNF/Serum: 0.085X + 0.056Y + 0.96Z = 11 kg
Total: X + Y + Z + 14.5 + 0.3 = 100 → X + Y + Z = 85.2 kg
Fat: 0.035X + 0.35Y = 10 kg
SNF/Serum: 0.085X + 0.056Y + 0.96Z = 11 kg
Total: X + Y + Z + 14.5 + 0.3 = 100 → X + Y + Z = 85.2 kg
From fat equation: Ratio Y/X can be determined; solve simultaneously:
Result: X ≈ 67.9 kg, Y ≈ 13.4 kg, Z ≈ 3.9 kg
Result: X ≈ 67.9 kg, Y ≈ 13.4 kg, Z ≈ 3.9 kg
Answer: Whole milk = 67.9 kg | Cream = 13.4 kg | SMP = 3.9 kg | Sugar = 14.5 kg | Stabilizer = 0.3 kg | Total = 100 kg ✓
🔢 Freezing Point Depression — Ice Cream
Problem 2: Find the temperature at which 50% of water freezes in mix (Fat 12%, Serum solids 11%, Sucrose 16%, Gelatin 0.3%).
Total solids = 12+11+16+0.3 = 39.3% → Water = 60.7%
Water frozen (50%) = 30.35% → Unfrozen water = 30.35%
Solutes in unfrozen water: Sugar+SS = 27% in 30.35% water
Concentration = 27/30.35 × 100 = 88.96 g/100g water
Concentration = 27/30.35 × 100 = 88.96 g/100g water
Using ΔTf = Kf × m (Kf = 1.86):
m_sucrose = (16/342)/0.3035 = 0.154 mol/kg
m_SS = (11/180)/0.3035 = 0.201 mol/kg
Total m = 0.355 mol/kg
m_sucrose = (16/342)/0.3035 = 0.154 mol/kg
m_SS = (11/180)/0.3035 = 0.201 mol/kg
Total m = 0.355 mol/kg
ΔTf = 1.86 × 0.355 = 0.66°C → Freezing temp = −0.66°C
Answer: Temperature = −0.66°C
Empirical Formula: Tf = −0.0054 × (Sugar+SS)² / (100−Fat) — used as quick approximation in practice.
Ice Cream Processing Overview
- Mix preparation: Blend ingredients (liquid + dry in correct order), no lumps
- Pasteurization: 68°C/30 min (LTLT) or 80°C/25 sec (HTST)
- Homogenization: 2000–2500 psi (breaks fat globules, improves texture)
- Aging: 4°C for 4–24 hours (crystallize fat, hydrate stabilizers)
- Freezing + whipping: −6°C continuous freezer; overrun 80–100%
- Hardening: −30 to −40°C blast freezer → final storage at −20°C
🔬 Platform Tests of Milk ⭐⭐⭐ HIGH PRIORITY
Platform Tests: Rapid evaluation tests carried out at Milk Collection Centers or Milk Reception Docks to make quick accept/reject decisions about incoming raw milk.
Classification of Platform Tests
| Category | Tests |
|---|---|
| Physical | 1. Organoleptic, 2. Sediment Test |
| Heat Stability | 3. COB Test, 4. Alcohol Test |
| Microbiological | 5. MBRT, 6. Resazurin (RRT) |
| Chemical/Biological | 7. Inhibitor Test |
| Composition | 8. Lactometer, 9. Gerber Fat, 10. SNF |
1. Organoleptic Test
| Sense | Normal | Abnormal → Cause |
|---|---|---|
| Sight | White/creamy, uniform | Pink (mastitis), Yellow (colostrum), Blue (water addition) |
| Smell | Clean, pleasant, slightly sweet | Sour (acidity), Rancid (lipase), Feed taint (onion/cabbage) |
| Taste | Slightly sweet, clean | Bitter (proteolysis), Metallic (Cu contamination) |
Advantage: No equipment needed, instant, free. Limitation: Subjective, cannot detect microscopic contamination.
2. Sediment Test
Purpose: Detect visible insoluble matter (dirt, feed, manure particles).
Apparatus: Sediment tester (25 cm filter), white lintine/cotton disc (32 mm diameter), 500 ml sample.
Procedure: Pour 500 ml milk through disc → dry disc → compare with standard discs.
Apparatus: Sediment tester (25 cm filter), white lintine/cotton disc (32 mm diameter), 500 ml sample.
Procedure: Pour 500 ml milk through disc → dry disc → compare with standard discs.
| Sediment (mg) | Grade | Action |
|---|---|---|
| 0.0 | Excellent | Accept |
| 0.2 | Good | Accept |
| 0.5 | Fair | Caution |
| 1.0 | Average | Investigate |
| ≥2.0 | Poor/Very Poor | Reject |
3. Clot-On-Boiling (COB) Test ⭐⭐⭐
Purpose: Detect high acidity milk (pH <5.6) or abnormal milk (colostrum, mastitis).
Principle: High acidity destabilizes casein → heat causes precipitation → visible clot.
Procedure: 5 ml milk in test tube → boiling water bath 5 min → examine for clot.
Principle: High acidity destabilizes casein → heat causes precipitation → visible clot.
Procedure: 5 ml milk in test tube → boiling water bath 5 min → examine for clot.
| Result | Observation | Interpretation | Action |
|---|---|---|---|
| PASS | No clot, uniform | Normal acidity, heat-stable | Accept |
| FAIL | Clots/flakes visible | High acidity OR abnormal | Reject |
4. Alcohol Test ⭐⭐⭐ (Very Important!)
Purpose: Rapid assessment of milk heat-stability and mineral balance — especially important for condensed milk and UHT processing.
Principle: 68% ethanol destabilizes casein when mineral balance is disturbed → positive test = heat-unstable.
Reagent: 68% ethyl alcohol by weight (must be exact — affects sensitivity).
Principle: 68% ethanol destabilizes casein when mineral balance is disturbed → positive test = heat-unstable.
Reagent: 68% ethyl alcohol by weight (must be exact — affects sensitivity).
Procedure (Must Know for Exam)
Take 5 ml of well-mixed milk sample in clean test tube
Add equal volume (5 ml) of 68% ethyl alcohol (1:1 ratio)
Mix by gently inverting tube 3–4 times (do NOT shake vigorously)
Examine immediately against good light
Record: NEGATIVE (smooth, no particles) or POSITIVE (curd particles/flakes)
| Result | Observation | Interpretation | Action |
|---|---|---|---|
| Negative | Smooth, uniform | Good mineral balance, heat-stable | Accept |
| Positive | Curd particles, flakes | Disturbed salt balance, heat-unstable | Reject |
⭐ What Alcohol Test Detects: (1) Disturbed mineral balance (Ca/Mg/phosphate ratio), (2) Developed acidity, (3) Abnormal proteins (colostrum, mastitis milk), (4) Heat instability for UHT/condensing. It is NOT purely an acidity test!
5. Inhibitor Test ⭐⭐⭐
Purpose: Detect antibiotics, drugs, pesticides — prevents inhibition of starter cultures in yoghurt/cheese making.
Principle: Inhibited milk → starter cannot grow → no acid production → compared with control.
Principle: Inhibited milk → starter cannot grow → no acid production → compared with control.
Procedure
Label 6 tubes: Tubes 1–3 = suspect milk | Tubes 4–6 = control (inhibitor-free) milk
Add 10 ml respective milk to each tube
Heat all tubes to 90°C for 3–5 min (destroy natural microflora)
Cool to starter temp (30–32°C for mesophilic OR 37–42°C for thermophilic)
Add 1 ml active starter to each tube; mix gently
Incubate at optimum temp for 3 hours; remove one tube/set at 1h, 2h, 3h
Measure titratable acidity or pH; compare suspect vs control
| Result | Interpretation | Action |
|---|---|---|
| Suspect acid = Control acid | No inhibitors | Accept for fermentation |
| Suspect acid < Control | Inhibitors present | Reject for fermented products |
| No acid in suspect | Strong inhibition (high antibiotic) | Reject completely |
6. Methylene Blue Reduction Time (MBRT) ⭐⭐⭐
Principle: Methylene blue (blue, oxidized) + bacterial metabolism → Leuco-methylene blue (colorless, reduced). More bacteria = faster decolorization = shorter reduction time.
Procedure
Add 1 ml methylene blue solution to clean test tube
Add 10 ml well-mixed milk; stopper tube
Mix by gentle inversion (3–4 times)
Place in water bath at 35°C; cover to exclude light
First reading at 30 min; then hourly until decolorized (4/5 color gone)
Record time in whole hours from last inversion to endpoint
| Time for Reduction | Quality Grade | Bacterial Count | Action |
|---|---|---|---|
| ≥5 hours | Very Good | <50,000/ml | Accept |
| 3–4 hours | Good | 50,000–5,00,000/ml | Accept |
| 1–2 hours | Fair | 5,00,000–20,00,000/ml | Accept with caution |
| ≤0.5 hours | Poor | >20,00,000/ml | Reject |
7. Resazurin Reduction Test (RRT) ⭐⭐⭐
Principle: Two-stage irreversible reduction:
Resazurin (BLUE) → Resorufin (PINK) → Dihydroresorufin (COLORLESS)
Color measured against Lovibond comparator disc (0–6).
Advantage over MBRT: Faster (10 min, 1hr, or 3hr variants), more objective color comparison.
Resazurin (BLUE) → Resorufin (PINK) → Dihydroresorufin (COLORLESS)
Color measured against Lovibond comparator disc (0–6).
Advantage over MBRT: Faster (10 min, 1hr, or 3hr variants), more objective color comparison.
| Disc No. | Color | Grade | Action |
|---|---|---|---|
| 6 | Blue | Excellent | Accept |
| 5 | Light blue | Very Good | Accept |
| 4 | Purple | Good | Accept |
| 3 | Purple-pink | Fair | Investigate |
| 2 | Light pink | Poor | Reject |
| 1 | Pink | Bad | Reject |
| 0 | White/Colorless | Very Bad | Reject immediately |
Memory Trick: RRT disc 6-4 = ACCEPT (Blue to Purple) | Disc 3 = CAUTION | Disc 2-0 = REJECT (Pink to White)
Comparative Summary — All Platform Tests ⭐⭐⭐
| Test | Time | Detects | Best For | Key Limitation |
|---|---|---|---|---|
| Organoleptic | 1–2 min | Off-odors, color, taste | Initial screening | Subjective |
| Sediment | 10–15 min | Visible dirt | Cleanliness | Misses dissolved contamination |
| COB | 5–7 min | High acidity, abnormal proteins | Heat stability | Misses low-acidity contaminated milk |
| Alcohol | 2–3 min | Mineral imbalance, heat instability | Condensed/UHT milk | Requires exact 68% alcohol |
| Inhibitor | 3 hours | Antibiotics, drugs, pesticides | Fermented products | Slow; doesn't ID specific inhibitor |
| MBRT | 30 min–5 hrs | Total bacterial count | General quality | Affected by O₂, light, temp |
| RRT | 10 min–3 hrs | Bacterial count, keeping quality | Rapid screening | Needs comparator; cost |
Reception Dock Testing Sequence
Step 1: Organoleptic Check (ALL cans)
↓
Step 2: Temperature Check (ALL cans)
↓
Step 3: Alcohol Test (ALL cans) ← Most critical step
↓
Step 4: COB Test (if alcohol positive or suspicious)
↓
Step 5: Sediment Test (random)
↓
Step 6: MBRT/RRT (random sampling)
↓
Step 7: Inhibitor Test (if for fermentation)
↓
Step 8: Composition Tests (Fat, SNF, Acidity — for payment)
🔢 Complete Numerical Problems — All Topics SOLVE ALL
N1. SNF in Cream
Milk has 3.5% fat, 8.7% SNF. Cream produced has 35% fat. Find SNF in cream.
Formula: %SNF_cream = [(100−F_cream) × SNF_milk] / (100−F_milk)
= [(100−35) × 8.7] / (100−3.5) = (65 × 8.7) / 96.5 = 565.5 / 96.5
Answer: SNF in cream = 5.86%
N2. Cream Acidity
Milk has 4.2% fat, 0.17% TA. Cream has 42% fat. Find cream TA.
Formula: Cream TA = (F_milk / F_cream) × TA_milk
= (4.2 / 42) × 0.17 = 0.10 × 0.17 = 0.017%
Answer: Cream acidity = 0.017%
N3. Butter Overrun
800 kg fat gives 1000 kg butter. Find overrun %.
%OR = [(B−F)/F] × 100 = [(1000−800)/800] × 100
= (200/800) × 100 = 25%
Answer: 25% overrun
N4. Butter Yield from % Overrun
If fat in churn = 500 kg and overrun = 18%, find butter yield.
Y = F × (100 + %OR) / 100
= 500 × (100+18) / 100 = 500 × 118 / 100 = 590 kg
Answer: Butter yield = 590 kg
N5. Cheese Standardization (C/F ratio)
1000 kg milk (4.5% fat, 2.7% casein). Add skim milk (2.8% casein) to get C/F = 0.70. Find skim milk needed.
Fat in 1000 kg = 45 kg. Required casein = 0.70 × 45 = 31.5 kg
Current casein = 27 kg. Deficit = 4.5 kg casein
SM = 4.5 / 0.028 = 160.7 kg
Answer: Add 160.7 kg skim milk
N6. Sugar Ratio in Condensed Milk
Condensed milk: 31% TMS, 43.1% sugar. Find sugar ratio.
%SR = [% sugar / (100 − %TMS)] × 100
= [43.1 / (100−31)] × 100 = [43.1 / 69] × 100
Answer: Sugar Ratio = 62.5%
N7. Sugar Addition Calculation
Condensed milk target: TMS = 28%, SR = 64%. Find % sugar needed. Then find sugar to add per 100L milk (TMS of milk = 12.5%).
% sugar = [(100−28) × 64] / 100 = (72 × 64)/100 = 46.08%
Concentration ratio = 28/12.5 = 2.24
Sugar in milk = 46.08 / 2.24 = 20.57% → per 100L: ~20.57 kg sugar
Answer: % sugar = 46.08% in condensed milk; ~20.57 kg per 100L milk
N8. Pearson's Square — Milk Standardization
Mix milk (6% fat) and skim milk (0.5% fat) to get 3% fat standardized milk. Find ratio of whole milk to skim milk.
Using Pearson's Square:
Whole milk (6%) ──────── (3 − 0.5) = 2.5 parts whole milk
\ Target: 3% /
\ /
Skim milk (0.5%) ─────── (6 − 3) = 3.0 parts skim milkRatio WM:SM = 2.5:3.0 = 5:6
Answer: Mix 2.5 parts whole milk (6%) with 3.0 parts skim milk (0.5%)
N9. Separator Velocity Comparison
Bowl speed increased from 5000 rpm to 6000 rpm. By what factor does separation velocity increase?
From Stoke's Law: V ∝ N² (centrifugal separation)
V₂/V₁ = (N₂/N₁)² = (6000/5000)² = (1.2)² = 1.44
Answer: Velocity increases by 1.44 times (44% increase)
N10. SMP Addition for Yoghurt
Add SMP (36% protein) to 1000 kg milk (3.0% protein) to reach 5.0% protein.
SMP = M × (Pt−Pm) / (Ps−Pt) = 1000 × (5.0−3.0) / (36−5.0)
= 1000 × 2.0 / 31.0 = 2000/31 = 64.5 kg
Answer: Add 64.5 kg SMP
📐 Diagrams Guide — What to Draw & How
⭐ Exam Strategy for Diagrams: ALWAYS draw a labeled diagram for 5-mark and 10-mark process questions. Even a rough but labeled diagram earns 2–3 marks guaranteed!
| Diagram | Must Draw? | Key Labels |
|---|---|---|
| Butter manufacturing flowchart | ✅ Practice | All 15 steps in order |
| Cheddar cheese flowchart | ✅ Practice | Include "Cheddaring" — unique step |
| Sweetened condensed milk flowchart | ✅ Practice | Vacuum pan, forewarming, sugar at end |
| Evaporated milk flowchart | ✅ Practice | Homogenization, pilot sterilization, sterilization |
| Set Yoghurt flowchart | ✅ Practice | Heat treatment conditions, pack THEN incubate |
| HTST Pasteurizer flow | ✅ Practice | Balance tank, regenerator, holder, FDV |
| Cream separator cross-section | ✅ Describe | Discs, bowl, top disc, skim/cream outlets |
| Platform test decision flowchart | ✅ Describe | All 8 steps in sequence |
| Vacuum pan (condensed milk) | ✅ Describe | 5 parts: heating surface, vapour space, entrainment sep., condenser, vacuum pump |
💡 Exam Tip — Flowchart Format
Always draw flowcharts with boxes and arrows. Write the temperature/time conditions next to each step. Use double boxes for critical steps. Label inputs (raw material) and outputs (finished product) differently.
📝 Previous Year Questions — Model Answers
High-Frequency 2-Mark Questions
| Question | Key Answer Points |
|---|---|
| What is churning? | Mechanical agitation of cream → fat globule membrane rupture → water-in-fat emulsion (butter). Temp: 7–8°C. |
| Define Overrun | %OR = [(Butter made − Fat used) / Fat used] × 100. Non-fat components incorporated into butter. |
| What is ripening of cream? | Holding pasteurized cream with starter culture (S.lactis etc.) at 8–10°C for 6–15 hrs to develop lactic acid and diacetyl flavor. |
| What is cheddaring? | Unique Cheddar process: draining curd slabs are stacked and turned at 38°C until pH 5.2–5.4 → forms parallel fiber structure. |
| What is Sugar Ratio? | %SR = [% sugar / (100−%TMS)] × 100. Optimum: 62.5–64.5%. Controls osmotic preservation of condensed milk. |
| What is alcohol test? | 68% ethanol + milk (1:1) → positive (clots) = heat-unstable, disturbed mineral balance → reject. Negative = accept. |
| MBRT interpretation | ≥5h = Very Good | 3–4h = Good | 1–2h = Fair | ≤0.5h = Poor. Shorter time = more bacteria. |
| What is COB test? | 5 ml milk boiled 5 min → clot = FAIL (reject). Detects high acidity or abnormal milk. |
| Types of yoghurt | Set type, Stirred type, Fluid, Frozen, Thermized. |
| Forewarming purpose | Kill microorganisms, prevent uninterrupted boiling in vacuum pan, control age-thickening viscosity. |
5-Mark Model Answers
Q: Describe the manufacturing process of butter. [5 marks]
Introduction: Butter is the fat-rich product made from cream by churning.
Process steps (with conditions):
1. Receiving milk → Preheating (38°C) → Separation (cream 35–40% fat)
2. Neutralization if needed (acidity >0.2%) with Na₂CO₃
3. Pasteurization (90°C/15 sec) → Cooling (7°C)
4. Ripening (optional): 8–10°C, 6–15 hrs, starter culture (S.lactis, S.diacetilactis)
5. Aging: 0–5°C, 2–8 hrs (crystallize fat)
6. Churning: 7–8°C (cream → butter granules + buttermilk)
7. Washing: cold water (remove residual buttermilk)
8. Working + Salting: knead to uniform texture, add 1–3% salt
9. Packaging + Storage: 4°C or below
PFA Standards: Fat ≥80%, Moisture ≤16%, Curd ≤1.5%, Salt ≤3%
Introduction: Butter is the fat-rich product made from cream by churning.
Process steps (with conditions):
1. Receiving milk → Preheating (38°C) → Separation (cream 35–40% fat)
2. Neutralization if needed (acidity >0.2%) with Na₂CO₃
3. Pasteurization (90°C/15 sec) → Cooling (7°C)
4. Ripening (optional): 8–10°C, 6–15 hrs, starter culture (S.lactis, S.diacetilactis)
5. Aging: 0–5°C, 2–8 hrs (crystallize fat)
6. Churning: 7–8°C (cream → butter granules + buttermilk)
7. Washing: cold water (remove residual buttermilk)
8. Working + Salting: knead to uniform texture, add 1–3% salt
9. Packaging + Storage: 4°C or below
PFA Standards: Fat ≥80%, Moisture ≤16%, Curd ≤1.5%, Salt ≤3%
Q: Explain the Alcohol Test for milk quality assessment. [5 marks]
Purpose: To rapidly assess heat stability of milk, especially for condensed milk and UHT processing. Detects disturbed mineral (Ca/Mg/phosphate) balance, not primarily acidity.
Reagent: 68% ethyl alcohol by weight (critical — must be exact concentration).
Procedure:
1. Take 5 ml milk in test tube
2. Add 5 ml of 68% ethyl alcohol (equal volumes = 1:1 ratio)
3. Invert gently 3–4 times — do NOT shake
4. Examine immediately against good light
Interpretation:
• Negative (no particles): Good mineral balance, heat-stable → ACCEPT
• Positive (curd particles/flakes): Disturbed salts, heat-unstable → REJECT
What it detects: Abnormal milk (colostrum, mastitis), developed acidity, disturbed mineral balance, heat instability.
Precautions: Use exactly 68% alcohol; read immediately; avoid vigorous shaking (false positive); ensure clean glassware.
Purpose: To rapidly assess heat stability of milk, especially for condensed milk and UHT processing. Detects disturbed mineral (Ca/Mg/phosphate) balance, not primarily acidity.
Reagent: 68% ethyl alcohol by weight (critical — must be exact concentration).
Procedure:
1. Take 5 ml milk in test tube
2. Add 5 ml of 68% ethyl alcohol (equal volumes = 1:1 ratio)
3. Invert gently 3–4 times — do NOT shake
4. Examine immediately against good light
Interpretation:
• Negative (no particles): Good mineral balance, heat-stable → ACCEPT
• Positive (curd particles/flakes): Disturbed salts, heat-unstable → REJECT
What it detects: Abnormal milk (colostrum, mastitis), developed acidity, disturbed mineral balance, heat instability.
Precautions: Use exactly 68% alcohol; read immediately; avoid vigorous shaking (false positive); ensure clean glassware.
Q: Describe MBRT test and its interpretation. [5 marks]
Principle: Methylene blue (blue) is reduced by bacterial metabolic activity to leuco-methylene blue (colorless). More bacteria = faster decolorization.
Reagent: Methylene blue tablet dissolved in 200 ml boiled distilled water → stored in amber bottle in dark. Prepare fresh weekly.
Procedure:
1. Add 1 ml methylene blue + 10 ml milk to stopper tube
2. Invert gently → place at 35°C water bath
3. First reading at 30 min, then hourly
4. Endpoint: 4/5 color has disappeared
Interpretation:
≥5 hours = Very Good (<50,000 bacteria/ml) → Accept
3–4 hours = Good (50k–500k/ml) → Accept
1–2 hours = Fair (500k–2M/ml) → Caution
≤0.5 hour = Poor (>2M/ml) → Reject
Factors affecting: Oxygen content, light exposure, temperature, cream/fat content, leucocyte count.
Principle: Methylene blue (blue) is reduced by bacterial metabolic activity to leuco-methylene blue (colorless). More bacteria = faster decolorization.
Reagent: Methylene blue tablet dissolved in 200 ml boiled distilled water → stored in amber bottle in dark. Prepare fresh weekly.
Procedure:
1. Add 1 ml methylene blue + 10 ml milk to stopper tube
2. Invert gently → place at 35°C water bath
3. First reading at 30 min, then hourly
4. Endpoint: 4/5 color has disappeared
Interpretation:
≥5 hours = Very Good (<50,000 bacteria/ml) → Accept
3–4 hours = Good (50k–500k/ml) → Accept
1–2 hours = Fair (500k–2M/ml) → Caution
≤0.5 hour = Poor (>2M/ml) → Reject
Factors affecting: Oxygen content, light exposure, temperature, cream/fat content, leucocyte count.
10-Mark Model Answers
Q: Describe the complete manufacturing process of Sweetened Condensed Milk with flowchart. [10 marks]
See the complete flowchart in the Condensed Milk section above. Write all steps with conditions. Key points to emphasize:
1. Reception: ≤10°C, alcohol test mandatory
2. Standardization: Fat:SNF = 1:2.44
3. Forewarming: 115–118°C, No Hold (modern flash method) — most important step, controls viscosity
4. Vacuum Condensing: ~55°C under partial vacuum, 2.5:1 ratio — heart of the process
5. Sugar addition: At END of condensing (not before) — to prevent viscosity increase and microbial heat resistance
6. Sugar Ratio: Must be 62.5–64.5% — preservative effect is osmotic pressure
7. Cooling & crystallization: Control lactose crystal size (<16 microns) to prevent sandiness
8. Packaging: Airtight cans; storage ≤10°C
PFA Standards: Fat ≥9%, TMS ≥31%, Sugar ≥40%
IS Standards: Acidity ≤0.35%, Bacteria ≤500/g, Coliforms = Negative
See the complete flowchart in the Condensed Milk section above. Write all steps with conditions. Key points to emphasize:
1. Reception: ≤10°C, alcohol test mandatory
2. Standardization: Fat:SNF = 1:2.44
3. Forewarming: 115–118°C, No Hold (modern flash method) — most important step, controls viscosity
4. Vacuum Condensing: ~55°C under partial vacuum, 2.5:1 ratio — heart of the process
5. Sugar addition: At END of condensing (not before) — to prevent viscosity increase and microbial heat resistance
6. Sugar Ratio: Must be 62.5–64.5% — preservative effect is osmotic pressure
7. Cooling & crystallization: Control lactose crystal size (<16 microns) to prevent sandiness
8. Packaging: Airtight cans; storage ≤10°C
PFA Standards: Fat ≥9%, TMS ≥31%, Sugar ≥40%
IS Standards: Acidity ≤0.35%, Bacteria ≤500/g, Coliforms = Negative
Q: Classify and explain Platform Tests of milk with procedures and interpretation. [10 marks]
Structure your answer as:
1. Introduction (2 lines): Platform tests = rapid quality assessment at reception dock for accept/reject decisions.
2. Classification table: Physical, Heat Stability, Dye Reduction, Chemical (with test names).
3. Describe 4–5 tests in detail with procedure and interpretation (Organoleptic, Alcohol, COB, MBRT, Inhibitor).
4. Comparative summary table.
5. Reception sequence flowchart.
Use all the content from the Platform Tests section. Focus especially on Alcohol Test and MBRT as these are highest-frequency exam topics.
Structure your answer as:
1. Introduction (2 lines): Platform tests = rapid quality assessment at reception dock for accept/reject decisions.
2. Classification table: Physical, Heat Stability, Dye Reduction, Chemical (with test names).
3. Describe 4–5 tests in detail with procedure and interpretation (Organoleptic, Alcohol, COB, MBRT, Inhibitor).
4. Comparative summary table.
5. Reception sequence flowchart.
Use all the content from the Platform Tests section. Focus especially on Alcohol Test and MBRT as these are highest-frequency exam topics.
✍️ Answer Writing Strategy — Maximum Marks
For 2-Mark Questions (2–3 sentences max)
Format
1. Define/state the concept in one clear sentence.2. Add one key number or mechanism.
3. Never write more than 3 sentences — you waste time.
For 5-Mark Questions
Format
1. One-line definition/introduction (½ mark)2. Procedure/process in numbered steps with conditions (2–3 marks)
3. Interpretation/results table if applicable (1 mark)
4. Small labeled diagram or flowchart (1 mark)
Target: 1 page, 5–8 minutes writing time.
For 10-Mark Questions
Format
1. Introduction + Definition (1 mark)2. Classification or types table (1–2 marks)
3. Process steps in detail with temperature/time conditions (4–5 marks)
4. Labeled flowchart/diagram (2 marks)
5. Standards (PFA/BSTI), Defects, or Comparison table (1–2 marks)
Target: 2–2.5 pages, 15–20 minutes writing time.
⭐ Guaranteed Mark Strategies:
• Always include a flowchart for any process question
• Always write temperature/time conditions (e.g., "72°C for 15 sec")
• Use tables whenever comparing two things
• Write PFA/IS standards when available — shows depth
• Underline key terms
• Start each major point on a new line with a number
• Always include a flowchart for any process question
• Always write temperature/time conditions (e.g., "72°C for 15 sec")
• Use tables whenever comparing two things
• Write PFA/IS standards when available — shows depth
• Underline key terms
• Start each major point on a new line with a number
🚨 Last Minute Tips — Night Before Exam
🧈 Butter Numbers
Fat ≥80% | Churn temp 7-8°C | Overrun: (B-F)/F × 100 | Ripening: 8-10°C / 6-15 hrs
🧀 Cheese Numbers
C/F = 0.68-0.70 | Moisture ≤43% | Scoring: Flavor 45, Body 30, Finish 15, Color 10
🥫 Condensed Milk
Forewarming: 115-118°C No Hold | SR = 62.5-64.5% | Vacuum pan 5 parts | Sandiness = bad crystal size
🫙 Yoghurt
L.bulgaricus + S.thermophilus | Heat: 90-95°C/30-45 min | Incubation: 42°C/3-4 hrs | pH endpoint: 4.5-4.6
🔬 Platform Tests
Alcohol: 68% / 1:1 / positive=reject | MBRT: ≥5h=VG, ≤0.5h=Poor | RRT disc: 6-4=Accept, 3=Caution, 2-0=Reject
🔥 Pasteurization
LTLT: 63°C/30min | HTST: 72°C/15sec | UHT: 135-150°C/2-5sec | Components: Balance tank → pump → regenerator → heater → holder → FDV → cooler
⚠️ Common Mistakes to Avoid:
• Mixing up Sugar Ratio formula with sugar % — SR = sugar/(100−TMS) × 100
• Forgetting cheddaring is UNIQUE to Cheddar (don't write it for cottage cheese)
• Writing wrong alcohol concentration (68%, not 70% or 63%)
• Forgetting that sugar is added at END of condensing (not beginning)
• Confusing MBRT time direction (shorter = worse quality = more bacteria)
• Forgetting homogenization in evaporated milk (49°C, two-stage 2000+500 psi) — critical step!
• Mixing up Sugar Ratio formula with sugar % — SR = sugar/(100−TMS) × 100
• Forgetting cheddaring is UNIQUE to Cheddar (don't write it for cottage cheese)
• Writing wrong alcohol concentration (68%, not 70% or 63%)
• Forgetting that sugar is added at END of condensing (not beginning)
• Confusing MBRT time direction (shorter = worse quality = more bacteria)
• Forgetting homogenization in evaporated milk (49°C, two-stage 2000+500 psi) — critical step!
🕐 Time Management in Exam
Read entire paper first (5 min) → attempt highest-mark questions you know best first → never leave any question blank → for unknown topics, write definition + whatever you know → always draw at least a rough flowchart
✅ Pre-Exam Checklist
🚀
You Got This!
You have everything you need in these notes. Stay calm, write structured answers, draw flowcharts, include conditions. Quality > Quantity. Good luck! 💪
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