Ice cream and frozen desserts

In short

Ice cream is a frozen dairy foam: a partly frozen aerated emulsion in which ice crystals, air cells, fat globules and a freeze-concentrated unfrozen serum coexist in roughly equal importance. Its quality is decided by mix composition (fat, MSNF, sugar, stabiliser-emulsifier, total solids) and by processing (pasteurisation, homogenisation, ageing, whipping-freezing, hardening). The topic is examined in Dairy Technology papers and in GATE-style questions through mix standardisation balances, overrun and freezing-point calculations, and legally through the FSSAI compositional standards that separate "ice cream" (milk fat) from "frozen dessert" (vegetable fat). Employers - Amul/GCMMF, Mother Dairy, Hatsun (Arun), Vadilal, Havmor, Kwality Wall's (HUL), Dinshaw's, Cream Bell, Baskin-Robbins India - interview on exactly these points, plus plant hygiene and cold-chain practice.

Explained

Definitions, classification and Indian standards

• Ice cream: product obtained by freezing a pasteurised mix of milk fat, milk solids-not-fat (MSNF), sugar, permitted stabilisers/emulsifiers, flavour and water, with incorporation of air.
• Frozen dessert / frozen confection: same technology but the fat may be wholly or partly edible vegetable fat/oil; it is legally not ice cream and must be labelled "frozen dessert".
• FSSAI (Food Safety and Standards (Food Products Standards and Food Additives) Regulations, 2011, as amended) prescribes, for ice cream: total solids ≥ 36%, milk fat ≥ 10%, protein ≥ 3.5% (w/w); medium-fat ice cream milk fat ≥ 5%, TS ≥ 30%; low-fat ice cream milk fat ≤ 2.5%, TS ≥ 26%, protein ≥ 3.0%.
• Weight per litre is specified so overrun cannot be unlimited - not less than 525 g/L for ice cream (lower figures apply to medium-/low-fat and to softy-type products). Frozen dessert mirrors these with "total fat" in place of milk fat.
• Stabilisers and emulsifiers together are limited (commonly 0.5% max, 0.75% where egg-based); permitted additives, flavours and colours are those in the FSSAI Additives Regulations. Exact limits are amended from time to time - confirm against the current gazette before quoting in a plant document.
• Other categories: softy/soft-serve (served at draw temperature, ~ −5 °C, not hardened), kulfi (traditional Indian, khoa/condensed-milk base, little or no overrun, slow-frozen in moulds/matkas), gelato (low overrun 20-35%, served warmer), sherbet (low milk solids, acidic, 1-2% fat), sorbet/water ice (no dairy fat), frozen yoghurt (fermented base), mellorine (vegetable-fat US term), novelties (bars, cones, sandwiches, choc-bars), dietetic/sugar-free, probiotic and protein-fortified variants.
• Labelling follows the FSSAI Labelling and Display Regulations, 2020 plus net-quantity declaration under the Legal Metrology (Packaged Commodities) Rules, 2011; vegetarian/non-vegetarian mark applies (egg-containing ice cream is non-veg).

Role of each mix constituent

• Milk fat (10-16%): richness, smooth texture, body, carrier of flavour; slows melting and ice growth. Too much → greasy, buttery, costly, slow whipping.
• MSNF / serum solids (9-12%): protein for whipping and air-cell stabilisation, lactose and minerals for body and freezing-point depression; cheapest solids source. Excess MSNF → sandiness (lactose crystallisation) and a salty/cooked flavour. Rule of thumb: MSNF should not exceed about 17% of the water in the mix (lactose solubility limit).
• Sugar (13-16%): sweetness, depresses freezing point, lowers hardness. Part replaced by corn syrup solids/glucose to improve body without over-depressing the freezing point.
• Stabilisers (0.1-0.3%): CMC, guar gum, locust bean gum, sodium alginate, carrageenan (to prevent whey-off), gelatin. They bind water, raise viscosity, limit ice recrystallisation during heat shock, and reduce shrinkage.
• Emulsifiers (0.1-0.2%): mono- and diglycerides, polysorbate 80, egg-yolk lecithin. They displace protein from the fat globule surface, promoting controlled partial coalescence of fat during whipping → dry, stiff extrusion, smooth texture and good shape retention.
• Water (60-64%): the phase that freezes; its purity and the unfrozen fraction govern scoopability.
• Total solids 36-42%: more solids = less water to freeze = smoother, but risk of heavy, soggy body.

Manufacturing process, step by step

1. Formulation and standardisation: solve a mass balance for fat, MSNF, sugar and stabiliser using milk, cream, SMP, condensed milk/khoa, butter/butter oil, sugar, water.
2. Mixing/blending: liquids into the vat at 40-50 °C; powders and sugar-stabiliser blends dispersed to avoid lumping; a high-shear mixer or funnel-type powder blender is used.
3. Pasteurisation: batch (vat) 68.3 °C for 30 min or HTST 79.5-82 °C for about 25 s - higher than for market milk because the mix is viscous and high in solids. Destroys pathogens, dissolves stabilisers, inactivates lipase.
4. Homogenisation: two-stage, at 63-77 °C, typically 2,500 psi first stage + 500 psi second stage (pressure lowered as fat content rises). Reduces fat globules below ~2 µm, prevents churning in the freezer, improves whipping and smoothness.
5. Cooling and ageing: cool rapidly to ≤ 4-5 °C and age at least 4 h (overnight is common). During ageing fat crystallises, proteins and stabilisers hydrate, viscosity rises, emulsifier displaces protein from the fat interface - ageing improves whipping and body.
6. Flavour/colour addition after ageing (volatiles would be lost in pasteurisation); fruit, nuts and ripple sauces are added after the freezer through a fruit feeder/variegator.
7. Freezing and whipping: in a continuous freezer the mix is pumped through a scraped-surface barrel with ammonia or R-404A/R-507 evaporating at about −25 to −30 °C; a dasher with scraper blades removes the frozen film and beats in metered air. Draw temperature −5 to −6 °C, with about half to two-thirds of the water frozen. Batch freezers are used for small/ artisanal lots.
8. Packaging (cups, tubs, cones, bars, family packs) and hardening in a blast freezer/plate hardening tunnel/hardening room at −30 to −40 °C until the core reaches −18 °C or below; fast hardening keeps crystals small.
9. Storage and distribution: store at −23 to −29 °C; distribution and retail cabinets at −18 °C or colder. Every temperature fluctuation causes melting-refreezing (heat shock) and coarse crystals.

Physical structure, overrun and freezing behaviour

• Structure at −18 °C: ice crystals 20-50 µm (≈ 30% by volume of the ice cream, i.e. about half the non-air volume), air cells 20-50 µm (≈ 50% of the volume at 100% overrun), partially coalesced fat globules and protein at the air-serum interface, and a very viscous unfrozen serum holding all the sugar, salts and most lactose.
• Overrun = the volume increase from incorporated air. Typical: hard pack 70-100%, premium/gelato 20-40%, softy 30-50%, kulfi near 0%, novelty bars 30-60%. Low overrun → heavy, icy, soggy; very high overrun → foamy, snowy, weak-bodied, and fails the weight-per-litre standard.
• Freezing curve: freezing begins near −2.5 °C; as ice forms, the remaining serum becomes more concentrated, so the freezing point falls progressively - there is no single freezing point, which is why ice cream is soft and scoopable over a range of temperatures.
• Not all of the water is ever frozen; even at −18 °C about 10% of the water stays unfrozen as a glassy/viscous syrup. Products with too much sugar stay soft and melt fast; too little sugar gives a brick-hard pack.
• Melting resistance and shape retention depend on fat partial coalescence, stabiliser level and air-cell stability.

Defects: cause and control

• Coarse/icy texture: slow freezing, low TS, heat shock, insufficient stabiliser → faster freezing, more solids, cold chain.
• Sandiness: gritty lactose crystals from excess MSNF or long warm storage → limit MSNF to the serum-point rule, use corn syrup solids.
• Greasy/buttery: poor homogenisation, high fat, churning in the freezer → correct pressures, check dasher speed.
• Weak/crumbly body: low TS or low stabiliser, excessive overrun.
• Soggy/heavy body: too much TS or sugar, low overrun.
• Gummy/pasty: excess stabiliser or MSNF.
• Shrinkage: air lost under pressure or temperature cycling in high-overrun, low-stabiliser product.
• Flavour defects: cooked, oxidised/metallic, rancid (lipase), stale MSNF, lacking or unnatural flavour.
• Hygiene: post-pasteurisation contamination at the freezer, fruit feeder and filler is the main microbiological risk; FSSAI process-hygiene criteria limit aerobic count and Enterobacteriaceae, require *Salmonella* absent in 25 g and control *Listeria monocytogenes* - a Schedule 4 FSMS/HACCP plan with CIP validation is expected in the plant.

Key points

• Ice cream - frozen aerated emulsion with milk fat; frozen dessert - same product with vegetable fat, must be so labelled.
• FSSAI ice cream minimum - 10% milk fat, 36% total solids, 3.5% protein, 525 g/L weight per litre.
• MSNF - milk solids-not-fat (protein + lactose + minerals); the cheapest solids and the whipping agent.
• Serum point rule - MSNF ≤ about 17% of mix water, else lactose crystallises and gives sandiness.
• Overrun - percentage volume increase due to air; 70-100% in hard pack, near zero in kulfi.
• Homogenisation - two-stage, ~2,500/500 psi at 63-77 °C; prevents churning, gives smoothness.
• Pasteurisation of mix - 68.3 °C/30 min (batch) or ~80 °C/25 s (HTST), stiffer than for milk.
• Ageing - ≥4 h at ≤5 °C; fat crystallises, proteins hydrate, emulsifier displaces protein - better whipping.
• Draw temperature - −5 to −6 °C with 50-65% of water frozen; hardening at −30 to −40 °C to a −18 °C core.
• Stabilisers bind water and resist recrystallisation; emulsifiers promote partial fat coalescence and dryness.
• Heat shock - temperature cycling that melts and refreezes water into large crystals; the main cause of iciness in the market.
• Freezing point depression - caused mainly by sugar and lactose; governs hardness and scoopability.
• Sandiness is lactose crystals; iciness is large ice crystals - different defects, different cures.
• Softy is drawn and served directly at about −5 °C with no hardening step.
• Partial coalescence, not full churning, is wanted - full churning gives butter granules.
• Cold chain - −18 °C or colder at every stage after hardening is the single biggest quality lever in India.
• Gelato/premium uses low overrun and high solids; served at a warmer temperature.

Formulas and examples

Example 1 - Overrun and the legal weight per litre. A freezer is fed 500 L/h of mix and discharges 925 L/h of ice cream. Mix weighs 1,090 g/L.

• Overrun = (925 − 500)/500 × 100 = 85%.
• Weight per litre of ice cream = 1,090/(1 + 0.85) = 589 g/L → above the 525 g/L minimum, so compliant.
• Maximum permissible overrun = (1,090/525) − 1 = 2.076 − 1 = 107.6%. Beyond this the pack fails the standard.

Example 2 - Mix standardisation (100 kg mix: 10% fat, 11% MSNF, 15% sugar, 0.4% stabiliser-emulsifier). Available: cream 40% fat (MSNF 5.4%), SMP with 96% MSNF, sugar, stabiliser blend, water.

• Fat required 10 kg → cream = 10/0.40 = 25.0 kg; MSNF from cream = 25 × 0.054 = 1.35 kg.
• MSNF still required = 11 − 1.35 = 9.65 kg → SMP = 9.65/0.96 = 10.05 kg.
• Sugar 15.0 kg, stabiliser-emulsifier 0.4 kg.
• Water = 100 − (25.0 + 10.05 + 15.0 + 0.4) = 49.55 kg.
• Check: TS = 10 + 11 + 15 + 0.4 = 36.4% (≥ 36, passes). Water = 63.6 kg; serum-point limit = 0.17 × 63.6 = 10.8% MSNF, so 11% is marginally high - drop MSNF to 10.5% or replace 1-2% sugar with corn syrup solids to be safe.

Example 3 - Freezing point and fraction of water frozen (same mix). Lactose ≈ 54.5% of MSNF → 11 × 0.545 = 6.0 kg lactose per 100 kg mix; sucrose 15 kg; water 63.6 kg. Molar mass of both sucrose and lactose = 342 g/mol.

• Moles = 15,000/342 + 6,000/342 = 43.86 + 17.54 = 61.40 mol per 100 kg mix.
• Molality = 61.40/63.6 = 0.9654 mol/kg water → ΔTf = 1.86 × 0.9654 = 1.80 °C, i.e. initial freezing point ≈ −1.8 °C (salts of MSNF push the practical value to about −2.3 to −2.5 °C).
• At draw temperature −5 °C: unfrozen fraction = 1.80/5 = 0.36 → 64% of the water is frozen.
• At −18 °C: 1.80/18 = 0.10 → 90% frozen; 10% of water remains as concentrated syrup, which is why the product is cuttable but not rock-solid.

Example 4 - Freezer refrigeration load for 100 kg mix/h (4 °C → −5 °C).

• Sensible above freezing: cp ≈ 3.3 kJ/kg·K, ΔT = 4 − (−1.8) = 5.8 K → 100 × 3.3 × 5.8 = 1,914 kJ.
• Latent: water 63.6 kg × 0.64 frozen = 40.7 kg × 334 = 13,594 kJ.
• Sensible below freezing: cp ≈ 2.1 kJ/kg·K over 3.2 K → 100 × 2.1 × 3.2 = 672 kJ.
• Total = 1,914 + 13,594 + 672 = 16,180 kJ/h = 4.49 kW = 1.28 TR (add ~20-25% for dasher work, surface heat gain and motor load → about 1.6 TR installed).

Example 5 - Ingredient cost per litre (indicative rates). Cream ₹180/kg, SMP ₹300/kg, sugar ₹45/kg, stabiliser blend ₹400/kg, flavour-colour ₹150 per 100 kg mix.

• 25.0 × 180 = ₹4,500; 10.05 × 300 = ₹3,015; 15 × 45 = ₹675; 0.4 × 400 = ₹160; flavour ₹150 → ₹8,500 per 100 kg mix.
• 100 kg mix at 1.09 kg/L = 91.7 L mix; at 85% overrun → 91.7 × 1.85 = 169.7 L ice cream.
• Ingredient cost = 8,500/169.7 = ₹50.1 per litre; packaging, energy, hardening, cold-chain, overheads and GST are added on top. (Edible ice/ice cream was moved in the 22 September 2025 GST rationalisation - verify the current slab for HSN 2105 before pricing.)

Where it is used

• Large dairy plants: Amul/GCMMF, Mother Dairy, Hatsun (Arun), Vadilal, Havmor, Dinshaw's, Cream Bell, Kwality Wall's - mix plants, continuous freezers, hardening tunnels, novelty and extrusion lines.
• Job roles: production/shift officer on the freezer line, R&D product developer (mix formulation, overrun and melt-down trials), QA/QC analyst (fat by Gerber/Rose-Gottlieb, TS, weight per litre, microbiology), cold-chain and distribution officer, FSSAI compliance and FSMS auditor.
• Franchise and QSR: soft-serve and gelato outlets, ice-cream parlours, food-court softy machines - mix powder/liquid mix supply, machine CIP and pasteurising-type softy machines.
• Allied industry: stabiliser-emulsifier blend suppliers, flavour and colour houses, SMP/WMP and butter-oil suppliers, cone and packaging makers, refrigeration and freezer OEMs.
• Regulatory and testing: FSSAI-notified labs and state food-safety officers checking fat, TS, weight per litre and the ice cream vs frozen dessert declaration.
• Entrepreneurship: small kulfi and artisanal gelato units under FSSAI registration/licence, and dairy-cooperative value-addition projects.

Interview questions

• Q: What legally distinguishes ice cream from frozen dessert in India? A: Ice cream must derive its fat from milk and carry at least 10% milk fat with 36% total solids and 3.5% protein; a frozen dessert may use vegetable fat and must be labelled "frozen dessert".
• Q: Why is the ice cream mix homogenised, and at what pressures? A: To break fat globules below about 2 µm so they cannot churn in the freezer and so the product whips and eats smooth - two-stage, roughly 2,500 psi plus 500 psi at 63-77 °C, pressure reduced as fat rises.
• Q: What happens during ageing and why can it not be skipped? A: Fat crystallises, protein and stabiliser hydrate, the emulsifier displaces protein from the fat surface and viscosity rises; without 4 h ageing the mix whips poorly and the body is weak and wet.
• Q: Define overrun and state the practical limit. A: The percentage increase in volume from incorporated air; it is limited by the legal minimum weight per litre - with a 1,090 g/L mix and a 525 g/L limit, the ceiling is about 108%.
• Q: Why is ice cream soft at −18 °C when water freezes at 0 °C? A: Sugars, lactose and salts depress the freezing point and the serum freeze-concentrates as ice forms, so about 10% of the water is still unfrozen syrup at −18 °C.
• Q: Distinguish sandiness from iciness. A: Sandiness is gritty lactose crystals from excess MSNF or warm storage; iciness is large ice crystals from slow freezing, low solids or heat shock.
• Q: What is heat shock and how do you prevent it? A: Temperature fluctuation that melts and refreezes water into coarse crystals; prevented by stable storage below −18 °C, adequate stabiliser, high solids and insulated fast distribution.
• Q: Why are emulsifiers added to a product that is already an emulsion? A: They partially destabilise it - displacing protein from the fat globule so controlled partial coalescence occurs during whipping, giving a dry, stiff extrusion and good shape retention.
• Q: Why is the mix pasteurised hotter than market milk? A: High fat, sugar and solids protect microorganisms and raise viscosity, so a higher time-temperature combination (68.3 °C/30 min or ~80 °C/25 s) is needed; it also hydrates stabilisers.
• Q: Where would you place the critical control points on an ice cream line? A: Pasteurisation (time-temperature), post-pasteurisation recontamination at freezer/fruit feeder/filler, hardening to a −18 °C core, and metal detection on the packed product.
• Q: A customer complains the pack has shrunk inside. What is your diagnosis? A: Air loss from a high-overrun, under-stabilised product subjected to temperature cycling or pressure change - lower overrun, raise stabiliser and total solids, and fix the cold chain.
• Q: How is kulfi technologically different from ice cream? A: It is a high-solids, concentrated-milk base with a cooked flavour, essentially no overrun and slow freezing in moulds, so the body is dense and chewy rather than light.

Common mistakes

• Confusing MSNF with total milk solids, or forgetting that cream and milk themselves carry MSNF in a standardisation balance.
• Computing overrun on the mix volume when the data are weights per litre (or vice versa) and quoting the wrong base.
• Ignoring the serum point rule and formulating 12-13% MSNF, then being surprised by sandiness.
• Adding volatile flavour before pasteurisation, or adding fruit/nuts before the freezer barrel.
• Treating ice cream as having a single freezing point instead of a freezing curve.
• Calling a vegetable-fat product "ice cream" in labels or answers - a direct FSSAI non-compliance.
• Assuming hardening is only storage: it is a process step with a target core temperature of −18 °C or below, and slow hardening coarsens crystals.

Related topics

Butter, ghee and cheese · Fermented milk products · Dairy engineering: refrigeration and cold chain · Milk chemistry: fat, protein and lactose · Food additives, stabilisers and emulsifiers · Dairy plant sanitation, HACCP and FSSAI compliance