UPMSP Vocational Dairy Technology cheat sheet

Average cow milk composition: water 87–88%, fat 3.5–4.5%, protein 3.2–3.5%, lactose 4.6–4.9%, ash 0.7–0.8%.

Buffalo milk is higher in fat (6–7%) and total solids (~16–17%) than cow milk (~12–13% TS); buffalo also lacks the yellow carotene colour.

Casein is ~80% of milk protein; whey proteins (β-lactoglobulin, α-lactalbumin) make up ~20% and are heat-labile.

Milk nitrogen fractions: total N × 6.38 = protein; casein N, whey N and non-protein N (NPN ~5–6% of total N) are the standard partition.

Lactose is a disaccharide of glucose + galactose, contributes ~30% of milk osmotic pressure, and is the substrate for lactic starters.

Milk salts are in dynamic equilibrium: calcium phosphate is split between colloidal (casein-bound) and soluble forms; heating and acid shift the balance.

Colostrum (first 3–5 days) has high protein, immunoglobulins and ash but low lactose; it is unfit for normal processing.

Freezing point of normal milk is about −0.54 °C; added water raises it toward 0 °C, which is the basis of the Hortvet freezing-point test.

Milk density at 20 °C is 1.028–1.032 g/mL; specific gravity 1.030–1.033 at 15.5 °C. Skim milk is denser than whole milk.

Titratable acidity of fresh milk is 0.14–0.16% lactic acid; values above ~0.18% indicate developed acidity or mastitis.

pH of fresh normal milk is 6.6–6.8; it falls toward 4.6 at the isoelectric point of casein, where curd forms.

Viscosity of milk at 20 °C is about 1.5–2.0 cP, roughly twice that of water; homogenisation and ageing increase it.

Refractive index ~1.3440–1.3480; used with a refractometer for detecting added water in milk.

Electrical conductivity of normal milk is ~4–6 mS/cm; mastitic milk is higher because of increased Na and Cl.

Surface tension ~50 dyn/cm (lower than water's 72) due to milk proteins and phospholipids; homogenisation lowers it further.

Colligative properties: osmotic pressure ~700 kPa, boiling point elevation ~0.55 °C - both are used to detect adulteration with water.

Reception sequence: unloading → weighing/measuring → sampling → platform tests → grading → filtration → chilling → storage.

Platform tests include organoleptic, Clot-on-Boiling (COB), alcohol test, titratable acidity, MBRT, fat and SNF - used to accept, grade or reject.

COB test: 5 mL milk boiled in a test tube; coagulation indicates acidity above ~0.20% and milk is rejected.

Alcohol test: equal volumes of milk and 68–70% neutral ethanol; curdling signals unstable milk (high acidity or mastitis).

MBRT (methylene blue reduction test) grades bacteriological quality: >5 h good, 2–5 h fair, <2 h poor.

Milk is weighed on a weigh bowl or measured in a calibrated dipstick tank; density correction is applied for volume-to-mass conversion.

Sampling for fat/protein uses a proportional sampler or a dipper; samples must be preserved (potassium dichromate or Bronopol) and kept cool.

Reception records include quantity, temperature, acidity, fat, SNF and supplier code - needed for payment and quality traceability.

Milk should be cooled to ≤4 °C within 2 h of milking; rapid cooling slows lactic acid bacteria and psychrotrophs.

Bulk milk coolers hold milk at 3–4 °C; storage beyond 48 h risks psychrotrophic growth (Pseudomonas, etc.) and lipolysis.

Chilling below 0 °C risks partial freezing, which damages the fat globule membrane and causes churning on agitation.

Insulated tankers transport chilled milk; temperature rise must stay under 2 °C during transit.

Psychrotrophic bacteria grow at refrigeration temperatures and produce heat-stable proteases/lipases that survive pasteurisation.

Cold-chain monitoring uses recording thermometers or data loggers; any break above 7 °C is treated as a quality deviation.

Pre-cooling on farm with plate coolers using well water plus chilled water reduces the load on the dairy's chillers.

Storage tanks must be agitated gently and periodically to prevent cream separation and to keep temperature uniform.

Filtration removes visible dirt and somatic cells; clarifiers use centrifugal force to remove fine sediment and leucocytes without removing fat.

Homogenisation forces milk through a valve at 150–250 bar; it reduces fat globules to <2 µm (mean ~0.5–1 µm), preventing cream separation.

Two-stage homogenisation (first ~150–200 bar, second ~30–50 bar) breaks clusters and gives a more stable emulsion.

LTLT pasteurisation: 63 °C for 30 min; HTST: 72 °C for 15 s; both achieve alkaline phosphatase inactivation (the pasteurisation indicator).

UHT treatment: 135–150 °C for 2–5 s followed by aseptic packaging; product is commercially sterile with a long shelf life.

Phosphatase test (or peroxidase test) verifies pasteurisation; a negative phosphatase result means the milk was properly heated.

Flow diversion valves on HTST pasteurisers automatically return under-heated milk to the balance tank.

Sterilisation in bottles uses 115–120 °C for 15–20 min (retort) and gives a brownish cooked flavour.

Cream grading by fat: half-and-half ~10–12%, light ~20%, whipping ~35–38%, plastic ~40–45%.

Cream separation uses a centrifugal separator; the fat content is controlled by the cream screw/back-pressure setting.

Butter must contain ≥80% milk fat, ≤16% moisture and ≤2% salt; overrun is controlled by churning and working.

Butter manufacture: cream ripening/ageing → churning → washing → salting → working → packing.

Ghee (clarified butter fat) must have ≥99.7% fat and ≤0.3% moisture; made by melting butter and removing moisture and curd by heating.

Ghee flavour comes from diacetyl, lactones and free fatty acids formed during fermentation and heating; the Reichert-Meissl value indicates authenticity.

Cream can be frozen for storage but must be homogenised before freezing to avoid fat destabilisation.

Adulteration checks in ghee use the Reichert-Meissl (RM), Polenske and Baudouin tests; vegetable fat lowers RM value below the legal ~28 minimum.

Curd (dahi) is made by inoculating boiled, cooled milk (~30–40 °C) with a lactic starter (Lactococcus lactis, Leuconostoc) and incubating 4–6 h.

Yoghurt uses thermophilic starters Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus at 42–45 °C for 3–5 h to pH ~4.6.

Lassi is a diluted, sweetened or salted fermented milk beverage made from curd by blending with water.

Chhana is obtained by coagulating hot milk (~70–80 °C) with citric acid or lemon juice and draining the whey; it is the base for rasogolla.

Paneer is made by coagulating hot milk (~85–90 °C) with citric acid or vinegar, pressing the curd in a hoop and cooling in chilled water.

Yield rule of thumb: chhana/paneer yield ~18–20% of milk weight; buffalo milk gives a firmer, higher-yield product.

Yoghurt defects: wheying off, sandy/grainy texture (from lactose crystals or starter phage) and over-acidity from extended incubation.

Post-acidification in yoghurt is controlled by cooling to <5 °C after fermentation to slow starter metabolism.

Spray drying: preheated concentrated milk is atomised and dried in hot air (inlet ~180–200 °C, outlet ~80–90 °C) to give powder with ≤4% moisture.

Roller (drum) drying gives a scorched flavour and lower solubility than spray drying; it is largely obsolete for milk powder.

Whole milk powder must have ≤4% moisture, ≤26% fat and ≥34% protein; skim milk powder has ≤4% moisture and ≥34% protein.

Instant milk powder is made by agglomerating particles and lecithinating them so the powder disperses readily in water.

Condensed milk: evaporation under vacuum removes water; sweetened condensed milk adds ~15–16% sucrose to preserve it.

Evaporated milk is sterilised after canning (unsweetened); sweetened condensed milk is preserved by sugar alone.

Reconstitution: 1 kg whole milk powder + ~7 kg water ≈ 8 kg whole milk; SMP + water + butterfat reconstitutes whole milk.

Powder quality checks: solubility index, scorched particles, bulk density, moisture and free fat.

Ice cream mix: fat 10–12%, MSNF 10–11%, sugar 14–16%, stabiliser 0.2–0.5%, emulsifier 0.2–0.5%, total solids ~36–40%.

Processing sequence: mix blending → pasteurisation (80–85 °C/15–20 s) → homogenisation (two-stage, ~150/50 bar) → ageing (2–24 h at 4 °C) → freezing → hardening.

Ageing allows fat crystallisation and protein/stabiliser hydration, improving overrun and texture.

Overrun is the % air incorporated: (volume of mix − volume of ice cream)/volume of ice cream × 100; typical 50–100%.

Continuous freezers whip air in and freeze to −5 to −6 °C; hardening at −25 to −30 °C brings the product to −18 °C or below.

Stabilisers (gelatin, CMC, guar gum) control ice crystal growth and meltdown; emulsifiers (mono/diglycerides) improve fat structure.

Ice cream defects: sandy texture (lactose crystals), icy crystals (temperature fluctuation), and shrinkage (air loss).

Frozen desserts replacing milk fat with vegetable fat are not legally 'ice cream' in many jurisdictions and are labelled as frozen dessert.

Cheese-making steps: standardisation → pasteurisation → starter addition → rennet coagulation → cutting → cooking → draining → cheddarring → salting → pressing → ripening.

Rennet (chymosin) cleaves κ-casein at Phe105-Met106, destabilising the micelle and causing coagulation.

Cheddar cheese has ~35–36% moisture and ~30% fat; moisture-in-fat-free-substance (MFFB) determines the cheese class.

Rennet casein is made by coagulating skim milk with rennet; acid casein uses acid to precipitate at pH 4.6.

Casein washing removes whey lactose; drying gives a product with ≥90% protein on a dry basis.

Cheese ripening uses starter bacteria, enzymes and sometimes moulds (Penicillium roqueforti for blue cheese, P. camemberti for surface-ripened).

Syneresis (whey expulsion) is controlled by cut size, cooking temperature and stirring - smaller curd and higher heat give drier cheese.

Cheese yield is roughly 10 kg milk per 1 kg cheese for hard varieties; fat and casein recovery drive the yield formula.

Raw milk flora: lactic acid bacteria, coliforms, psychrotrophs, thermodurics, spores and occasionally pathogens (Salmonella, Listeria, E. coli O157).

Pasteurisation kills vegetative pathogens but not spores; Bacillus cereus and Clostridium spores survive and limit shelf life.

Coliform count is an indicator of hygiene and post-pasteurisation contamination; the standard is <10 cfu/mL for pasteurised milk.

Standard plate count (SPC) at 30 °C for 48 h gives the total viable bacterial load; high counts indicate poor hygiene or cooling.

Somatic cell count (SCC) above ~400,000 cells/mL indicates mastitis; the bulk tank limit is typically ≤500,000 cells/mL.

Antibiotic residues in milk inhibit starter cultures and are tested by the Delvotest or similar inhibitor assays.

Psychrotrophs such as Pseudomonas produce heat-stable proteases and lipases that cause bitterness and rancidity after UHT storage.

Spore-formers in UHT milk cause spoilage (bitty cream, sweet curdling); their source is farm and plant sanitation.

Mesophilic starters (Lactococcus lactis, Leuconostoc) work at 20–30 °C for cultured buttermilk and dahi; thermophilic starters (S. thermophilus, L. bulgaricus) work at 40–45 °C for yoghurt.

Starter activity is checked by titratable acidity development, coagulation time and phage testing.

Bacteriophage attack causes slow or failed acid production; rotation of starter strains and sanitised air handling reduce the risk.

Freeze-dried (lyophilised) cultures are stored at −20 °C or below; DVS (direct vat set) cultures are added directly to the vat.

Starter propagation uses heat-treated (95 °C/30 min) skim milk to destroy inhibitors and phage.

Quality control plan: raw milk platform tests, process checks (phosphatase, temperature), finished product tests (fat, SNF, acidity, MBRT, coliforms).

HACCP identifies CCPs such as pasteurisation temperature/time and metal detection; critical limits are monitored and recorded.

Cleaning validation uses ATP swabs and rinse-water tests; residual milk soil and sanitiser residues must be absent.

CIP (clean-in-place) sequence: pre-rinse → alkaline wash (1–2% NaOH at 70–80 °C) → intermediate rinse → acid wash (0.5–1% HNO3) → final rinse → sanitise.

Alkaline wash removes fat and protein; acid wash removes mineral scale (milk stone).

Flow velocity in CIP lines must be ≥1.5 m/s to achieve turbulent cleaning; the contact time and temperature are recorded.

Plate heat exchangers are cleaned by back-flushing and CIP; gasket condition is checked for leaks and product-to-product cross-contamination.

Separators and homogenisers require manual dismantling for inspection at defined intervals.

Safety: steam lines, hot water and rotating equipment need guarding; lockout/tagout is applied before maintenance.

Chemical hazards: NaOH and HNO3 cause burns; PPE (gloves, goggles, apron) and eyewash stations are mandatory.

Boiler and refrigeration (ammonia) systems require trained operators and leak detection; ammonia is toxic and flammable at high concentration.

Milk fat is a triglyceride mixture with ~65% saturated fatty acids; butyric acid (C4) is characteristic and detected by the Reichert-Meissl value.

Casein micelles (~50–300 nm) are stabilised by κ-casein; acid or rennet destabilises them and causes coagulation.

Isoelectric point of casein is pH 4.6, where the net charge is zero and curd forms.

Maillard reaction between lactose and lysine during heating causes browning and loss of available lysine in UHT and dried milk.

Lipolysis releases free fatty acids and causes rancidity; it is catalysed by milk lipase, which is inactivated by pasteurisation.

Oxidation of milk fat gives tallowy/cardboard flavours; copper and light accelerate it, while ascorbic acid and low oxygen slow it.

Lactose crystallisation in concentrated milk and ice cream gives a sandy texture; α-lactose monohydrate is the stable crystal form.

Milk protein has a high biological value (~90) and is rich in lysine, which is limiting in cereals.

Gerber method: fat % = (butyrometer reading × 18)/weight of milk (11.33 g for milk); sulphuric acid and amyl alcohol are used.

Babcock method uses sulphuric acid and centrifuging; the fat column is read directly on the calibrated bottle neck.

Kjeldahl nitrogen × 6.38 gives total protein; the factor 6.38 reflects milk's 15.67% nitrogen content.

Lactometer (hydrometer) reads specific gravity; a reading of 1.030 at 15.5 °C is normal, and temperature correction is applied.

Titratable acidity is measured by titrating with 0.1 N NaOH using phenolphthalein; 1 mL of 0.1 N NaOH per 10 mL milk corresponds to 0.09% lactic acid.

MBRT and resazurin tests are rapid bacteriological grading tests; the resazurin test uses colour change from blue to pink to white.

Freezing-point (cryoscopic) test detects added water: normal milk freezes at −0.54 °C; each 1% added water raises it by ~0.0054 °C.

Adulterant tests: starch (iodine → blue), cane sugar (resorcinol → red), urea (DMAB test), and detergent (methylene blue/chloroform).