Dairy Science & Technology · Dairy Engineering & Plant Operations · also Dairy Plant Sanitation, Cleaning and Sanitisation
How dairy plants are cleaned and sanitised: fouling chemistry, detergents, sanitisers, CIP design and verification, and hygienic equipment design.
In the exams: ICAR AICE subject 37 Unit 3 and subject 35a Unit 3; ICAR AIEEA-PG group 16 (dairy plant hygiene and sanitation); GATE XL-U Section 3 (CIP)
Cleaning and sanitation are the invisible half of dairy processing. Milk is an ideal medium for micro-organisms, dairy equipment runs warm and wet, and heat treatment leaves deposits on every heated surface. Without effective cleaning, a plant loses heat-transfer efficiency, makes spoiled or unsafe products, and risks recalls. With it, the same equipment can run for decades producing safe food. Cleaning also uses large amounts of water, energy and chemicals, so good design and control matter for cost and the environment.
This manual covers fouling and soil types; the mechanism of soil removal (time, temperature, chemistry and mechanical action); detergents; sanitisers; CIP systems; CIP circuit design and flow velocity; cleaning of membranes, evaporators and dryers; verification by ATP, swabs and inspection; hygienic design principles and the 3-A and EHEDG guidance; biofilm control; and pest control and personal hygiene. The equipment being cleaned is described in dairy-processing-equipment, membrane cleaning in more depth in membrane-processing-dairy-ingredients, evaporators and dryers in evaporation-drying-dairy, HACCP in market-milk-processing, and general food plant sanitation for the wider food industry in the food technology track's food-plant-sanitation; this manual concentrates on dairy practice.
ICAR AICE-JRF/SRF Dairy Technology (subject 37, Unit 3) covers current trends in cleaning and sanitisation of dairy equipment, automation, ultrasonic cleaning, biofilms, bio-detergents, innovations in sanitisers, the mechanism of fouling and soil removal, assessing cleaning effectiveness and water conservation; ICAR AIEEA-PG Dairy Science names dairy plant hygiene and sanitation. GATE XL Food Technology includes cleaning-in-place. Concentrations, temperatures and times are representative values; chemical suppliers' instructions, validation in the plant and local regulations govern practice.
Cleaning in a dairy means removing everything from product-contact surfaces that should not be there: product residues, deposits formed by heat, mineral scale, biofilms and, finally, micro-organisms. Unheated surfaces such as tanks, pipes and fillers carry a thin film of milk containing fat, protein, lactose and minerals; it is relatively easy to remove if cleaning follows promptly, but if it dries it becomes much harder. Heated surfaces in pasteurisers, UHT plants and evaporators carry fouling deposits formed by heat, which are the most difficult soils in the dairy. Fat films are left by cream, butter and cheese; caramelised lactose and protein form brown deposits in high-temperature equipment; and powder plants accumulate dry deposits. Each soil type needs a different chemistry, and knowing which soil is present is the starting point for designing a cleaning programme.
Fouling from heated milk is commonly classed into two types. Type A deposits form mainly between about 75 and 110 °C, as in the heating and holding sections of pasteurisers and the early stages of UHT heating: they are soft, voluminous, white or cream-coloured and consist mainly of protein (largely denatured beta-lactoglobulin, with casein) with a substantial mineral fraction and some fat. Type B deposits form at higher temperatures, above about 110 °C, as in UHT heaters: they are hard, compact, grey and granular and consist mostly of minerals, mainly calcium phosphate, with less protein. The mechanisms differ. Type A fouling follows the denaturation of beta-lactoglobulin: unfolded protein aggregates and adheres to surfaces, binding calcium phosphate and other components. Type B fouling is dominated by calcium phosphate, whose solubility falls as temperature rises, so it precipitates on hot surfaces. Fouling is influenced by milk quality (age, pH, whey protein content), preheating (a holding step that denatures whey protein before the main heater reduces deposits in hotter sections), surface temperature, flow velocity and air bubbles. On farms, milkstone — a hard deposit of calcium phosphate, protein and fat on milking equipment and bulk tanks — forms when acid cleaning is neglected.
Fouling reduces heat transfer (deposits are poor conductors), raises pressure drop and pumping energy, can make the product temperature fall below the legal limit in a pasteuriser or below the required sterilising temperature in UHT, and shortens run times. Deposits also protect and feed micro-organisms, including thermophilic spore-formers, and can flake off into the product. Plants monitor fouling indirectly by the increase in steam or hot water temperature needed to hold product temperature, or by the rise in pressure drop across heat exchangers, and stop production for cleaning before limits are reached. Reducing fouling by design and operation — preheating and holding, high velocity, small temperature differences between heating medium and product, removal of air — extends run times and saves cleaning chemicals, water and energy.
Cleaning depends on four interacting factors, often drawn as Sinner's circle after the German chemist who described it: time (how long the cleaning solution acts), temperature, chemistry (the type and concentration of detergent) and mechanical action (flow, turbulence, spray impact or scrubbing). For a given soil and surface, a fixed amount of cleaning 'work' is needed, and the four factors can be traded against one another: a weaker solution can be compensated by higher temperature or longer time; poor mechanical action needs stronger chemistry or more time. Reducing one factor without increasing another gives incomplete cleaning. Practical limits apply to each: temperature is limited by energy cost, safety and the risk of baking soil on or damaging gaskets and membranes; chemical concentration by cost, corrosion and effluent; time by production schedules; and mechanical action by pump capacity and equipment design. CIP programmes are designed by choosing a combination that reliably cleans the worst-case soil.
Soil removal proceeds through several steps. The cleaning solution must wet the soil and penetrate it; detergents with surfactants lower surface tension and improve wetting. Alkaline solutions swell and hydrolyse proteins, breaking them into smaller, soluble fragments, and saponify fats into soluble soaps while emulsifying the rest; acid solutions dissolve mineral deposits such as calcium phosphate. Sequestrants keep dissolved calcium and magnesium from re-precipitating. The loosened soil must then be carried away by the flowing solution, which requires sufficient wall shear stress: in pipes this means turbulent flow at an adequate velocity, and on tank walls it means a continuous falling film or direct jet impact. Finally, the soil must stay suspended or dissolved and be rinsed out, without redepositing elsewhere in the circuit. Temperature speeds all these chemical reactions and lowers viscosity, but excessive temperature on protein soils can denature them further and make them harder to remove, which is one reason pre-rinses are done with cool or warm, not hot, water.
Several newer techniques supplement conventional chemical CIP. Ultrasonic cleaning uses high-frequency sound waves in liquid to create cavitation bubbles whose collapse dislodges soil from surfaces; it is used for small parts, membranes in some trials, and filler components that are difficult to clean by flow. Bio-detergents based on enzymes (proteases, lipases, amylases) and biosurfactants clean at lower temperatures and with less aggressive chemistry, reducing energy use and effluent load. Electrolysed water, produced by electrolysis of dilute salt solution, gives alkaline and acidic (hypochlorous) streams that can clean and sanitise. Automation with real-time sensors — turbidity, conductivity and fouling monitors — allows cleaning to stop when the circuit is clean rather than after a fixed time, saving water, chemicals and time. These techniques are adopted where they are validated for the specific equipment and soil.
Alkaline detergents are the main cleaning agents for protein and fat soils. Sodium hydroxide (caustic soda) is the workhorse of dairy CIP; it is commonly used at around 0.5–1.5 per cent for general circuits and at higher concentrations, around 1.5–2 per cent or more, for heavily fouled heat-treatment equipment, at temperatures commonly between about 70 and 85 °C. It dissolves protein deposits, saponifies fat and is also bactericidal, but it is corrosive to aluminium and harmful to skin and eyes, and it reacts with calcium in hard water to form scale unless sequestrants are present. Potassium hydroxide is similar and sometimes preferred for solubility. Milder alkalis — sodium carbonate, sodium silicates (which inhibit corrosion of soft metals) and phosphates — are used in manual cleaning and for sensitive surfaces. Commercial formulated alkaline detergents combine caustic with sequestrants and surfactants, making them more effective at lower concentration. Concentration is controlled in CIP systems by conductivity measurement and checked by titration.
Acid cleaners dissolve mineral deposits — calcium phosphate, milkstone, waterstone (scale from hard water) — and neutralise residual alkali. Nitric acid is widely used in dairy CIP at concentrations commonly around 0.5–1 per cent and temperatures around 60–70 °C; it also helps maintain the passive layer on stainless steel. Phosphoric acid is a less aggressive alternative, often in formulated products with surfactants; organic acids such as citric, sulphamic and glycolic acid are used in some applications and for membranes. Acids must be compatible with materials (hydrochloric acid is not used on stainless steel because chlorides cause pitting) and with gaskets. The order of alkali and acid steps depends on the soil: alkali first is usual for protein-rich soils, while acid first can be better for mineral-rich (type B) deposits, which may need an acid–alkali–acid sequence.
Sequestrants (chelating agents) bind calcium and magnesium ions so that they do not precipitate as scale or reduce detergent effectiveness; examples are EDTA, gluconates, phosphonates and polyphosphates, chosen with an eye to effluent rules (some phosphates and EDTA are restricted). Surfactants — anionic, non-ionic, amphoteric — lower surface tension so solutions wet and penetrate soils and emulsify fat; low-foaming surfactants are essential in CIP, because foam disrupts pumps and flow. Enzymatic cleaners, mainly proteases, sometimes with lipases and amylases, remove protein soils at mild pH and temperature and are used for membranes and other sensitive equipment, usually followed by alkaline and acid steps. Water quality also matters: hardness salts form scale and consume detergent, iron and manganese stain, and chlorides corrode stainless steel; soft or treated water and good rinsing water are part of a cleaning system. Single-phase (one-step) formulated detergents that combine alkaline cleaning with sequestration are used in some plants to save time and water, at the expense of less flexibility.
After cleaning, surfaces still carry some micro-organisms, which sanitising reduces to a safe level; sanitising is effective only on clean surfaces, because soil shields micro-organisms and inactivates many chemicals. Heat is the simplest and most reliable sanitiser for closed systems: circulating hot water, commonly at around 85–90 °C or higher for a set contact time at the coldest point of the circuit, or steam, kills vegetative cells without leaving residues. Its drawbacks are energy cost, slow heating and cooling of large equipment, thermal stress, and the risk of baking on any residual soil. Hot water sanitising is common for pasteurisers, pipelines and fillers; higher temperatures and pressures are used to sterilise UHT and aseptic systems.
Chlorine-based sanitisers, mainly sodium hypochlorite, release hypochlorous acid, a powerful oxidising agent that kills bacteria, yeasts, moulds and viruses quickly and is cheap. Typical sanitising concentrations are of the order of 100–200 mg/L available chlorine for food-contact surfaces, within the limits set by local regulation. Chlorine is more active at slightly acidic to neutral pH, where more of it is present as hypochlorous acid, but more corrosive there; it is inactivated by organic matter, corrodes stainless steel at high concentration, temperature or long contact (pitting), and can form chlorinated by-products. Chlorine dioxide is a related, more selective oxidant. Iodophors are complexes of iodine with surfactants, used at concentrations commonly around 12.5–25 mg/L available iodine in acidic solution; they are effective, less corrosive than chlorine at use levels, give a visible colour that shows they are present, but stain plastics and gaskets, lose activity above about 45–50 °C, and can leave iodine residues that must be controlled.
Quaternary ammonium compounds (QACs) are cationic surfactants. They are stable, odourless, non-corrosive and leave a residual antimicrobial film, which is useful on floors, walls and drains but undesirable on product-contact surfaces where residues can carry into food and inhibit starter cultures; they are weaker against Gram-negative bacteria and spores, are inactivated by hard water and anionic detergents, and foam, so they are rarely used in CIP circuits. Peracetic acid (PAA), an equilibrium mixture of peracetic acid, hydrogen peroxide and acetic acid, is a strong oxidiser effective against bacteria, spores (at higher concentrations), yeasts, moulds and viruses, works at low temperatures, is less affected by organic matter than chlorine, does not foam, and breaks down to acetic acid, water and oxygen. It is widely used in dairy CIP and for aseptic filler sanitising and cold sanitising of membranes (where compatible), though it is pungent and corrosive to some metals and elastomers at high concentrations. Hydrogen peroxide, ozone and other agents are used in specific applications. Sanitiser selection considers spectrum, contact time, temperature, material compatibility, residues and the regulatory status of no-rinse use, which differs by country.
Sanitiser concentration must be high enough to work within the available contact time and low enough to avoid corrosion, residues and waste. Plants prepare solutions from concentrates by dilution calculations — for example, 1,000 L of a 200 mg/L available chlorine solution needs 200 g of available chlorine, about 2 kg of a 10 per cent hypochlorite concentrate — and check them with test strips, titration or meters. Sanitiser efficacy is often described by log reduction: a sanitiser that reduces 10⁶ organisms per unit area to 10¹ has achieved a five-log reduction, a common benchmark in efficacy testing on clean surfaces. Contact time, temperature and pH must match the supplier's validated conditions, and solutions must be replaced when exhausted by organic load.
Cleaning-in-place (CIP) cleans equipment without dismantling it, by circulating rinse water and cleaning solutions through pipes, tanks and machines under controlled conditions. A CIP system consists of tanks for water, alkaline detergent, acid and recovered rinse water; a supply pump that delivers solution to the circuit at the required flow and pressure; a heat exchanger (plate or tubular, steam-heated) to bring solutions to temperature; dosing equipment for concentrated chemicals; instrumentation for temperature, conductivity (concentration), flow and level; a return pump (or gravity return, or the circuit's own pump) to bring solution back from tanks; and a control system that runs programmed sequences and records each cleaning. CIP gives consistent, repeatable, documented cleaning, reduces labour and exposure of operators to chemicals, and allows cleaning of closed equipment that cannot be cleaned by hand.
In single-use (once-through) systems, cleaning solution is made up fresh for each clean, used once and discharged. They suit heavily soiled equipment such as UHT plants and evaporators, where the solution becomes heavily contaminated, and small or decentralised systems; they use more chemicals and water but avoid recontamination. In re-use (recovery) systems, the detergent solution is returned to its tank after use, topped up to strength and reused for several cleans until it becomes too dirty, when it is discarded; rinse water from final rinses is recovered and used for pre-rinses of the next clean. Re-use systems save chemicals, water and energy and are standard for lightly soiled circuits such as milk reception lines, tanks and pasteurisers. Many plants combine both, using re-use for most circuits and single-use for the heaviest soils.
A centralised CIP station serves many circuits across the plant from one set of tanks, with long supply and return lines; a decentralised system uses smaller CIP units located near the equipment they clean (satellite systems), with shorter lines, less heat and water loss, and less risk of cross-contamination between plant areas such as raw and pasteurised sides. Large plants often use a central tank farm with satellite units. A typical programme for a pasteuriser or pipeline is: pre-rinse with recovered or fresh water until the return is clear; alkaline circulation (for example 0.5–1.5 per cent sodium hydroxide at about 75 °C for 10–20 minutes); intermediate rinse; acid circulation (for example 0.5–1 per cent nitric acid at about 60–70 °C for 5–10 minutes); final rinse with potable water; and sanitising with hot water or a chemical sanitiser, sometimes just before production. Heavily fouled heat-treatment sections need stronger, hotter and longer cycles, and some plants use an intermediate clean during long runs. Programmes are validated for each circuit and recorded every time.
CIP uses a large share of a dairy's water, heat and chemicals and generates much of its effluent load, so efficiency matters. Measures include recovering final rinse water for pre-rinses, re-using detergent solutions, recovering product from the start of the pre-rinse (product push-out with water or pigging) instead of sending it to drain, using conductivity and turbidity to separate phases precisely, optimising temperature and time, recovering caustic by nanofiltration, and neutralising alkaline and acid effluents against each other before discharge. Concentrated alkalis, acids and oxidising sanitisers are hazardous: they cause severe burns, react dangerously if mixed (acids with hypochlorite release chlorine gas), and need safe storage, bunding, labelled dosing systems, personal protective equipment, eye-wash stations and training. Automated dosing from bulk containers reduces handling and exposure.
For pipes, the key design parameter is flow velocity, which determines turbulence and wall shear stress. A velocity of at least about 1.5 m/s is widely used as a design target for CIP of dairy pipelines (some guidelines use 1.5–2.0 m/s), which gives fully turbulent flow; the Reynolds number Re = ρ v D ÷ μ, with water at 1.5 m/s in a 63.5 mm pipe, is around 95,000, far above the laminar–turbulent transition. The required flow rate follows from velocity and pipe area: Q = v × π D² ÷ 4; for a 63.5 mm internal diameter pipe at 1.5 m/s it is about 17 m³/h. Larger pipes need much more flow, so circuits with mixed pipe sizes are designed for the largest diameter, and very large lines may be cleaned in sections. Pipes must slope to drain, be free of dead legs or have dead legs short enough to be cleaned by turbulent flow (often expressed as a maximum length in pipe diameters), and have all branches, valve seats and instrument fittings exposed to cleaning flow; valves in a circuit are pulsed (opened and closed during cleaning) so that seats and seals are cleaned. Air in the circuit and poor return flow are common causes of failure.
Tanks are cleaned by spray devices that wet the whole interior. Static spray balls are perforated spheres that distribute solution over the upper walls, from which it runs down as a falling film; they are simple and cheap but rely on a continuous film and therefore need sufficient flow, often specified per metre of tank circumference (a commonly quoted rule of thumb is roughly 25–35 L per minute per metre for vertical tanks), and they clean mainly by chemistry and film flow rather than impact. Rotating spray heads spin under the force of the liquid and give better coverage with less water. Rotary jet heads (orbital cleaners) direct a few high-velocity jets that move in a pattern over the whole surface, cleaning by impact; they are effective for large tanks and difficult soils and use less solution, but need higher pressure and longer cycle times for full coverage. Shadow areas behind agitators, ladders, sensors and manway necks must be reached, sometimes with extra spray devices. Tank outlets and return lines must remove liquid as fast as it is supplied, or a pool forms and the lower part of the tank is not cleaned by impact. Air vents must allow air in during cooling to prevent vacuum damage.
CIP circuits must never allow cleaning solutions to contaminate product. Older plants used physical separation by swing bends or flow plates (a pipe section that is physically connected either to the product line or to the CIP line, never both); modern plants use valve clusters with double-seat mix-proof valves that allow product and CIP to flow in adjacent lines with a leakage chamber open to drain between them, or block-and-bleed arrangements of two valves with a drain between. Control systems interlock valves so that product cannot be routed into a circuit being cleaned. Conductivity sensors detect the interface between rinse water and chemicals and between product and water, so phases can be separated, recovered or discarded correctly, saving product and chemicals.
Membrane plants need cleaning programmes matched to the membrane material, as described in membrane-processing-dairy-ingredients. Polymeric membranes (polysulfone, polyethersulfone, polyamide) have limits on pH, temperature and chlorine; programmes therefore often combine enzymatic or mild alkaline cleaners with surfactants, acid steps for mineral removal and compatible sanitisers (hydrogen peroxide or peracetic acid for polyamide; controlled chlorine for chlorine-tolerant polymers). Ceramic membranes tolerate strong alkali and acid at high temperature. Cleaning is verified by clean water flux recovery, and cleaning chemistry must not damage the membrane or shorten its life. Spiral-wound modules have narrow feed channels that need adequate cross-flow during cleaning.
Evaporators accumulate heavy deposits in the hot first effects and finishers, including denatured protein and calcium phosphate, and in long runs harbour thermophilic spore-formers. They are cleaned in place, often with single-use or dedicated systems: alkaline solutions at higher concentration and temperature than for pasteurisers, followed by acid, distributed through the same product distribution system so that every tube is wetted, and sometimes with additional spray devices in vapour separators and ducts. Run length between cleans is set to control both fouling and spore build-up. Condensers and vapour ducts may need periodic cleaning too, and cleaning solutions must not be carried over into condensate recovery systems.
Spray dryers are cleaned less often than wet equipment and in different ways. Dry cleaning — brushing, vacuuming and compressed-air removal of deposits — is used between runs on some surfaces, because introducing water into a powder plant can create sticky deposits and favourable conditions for bacteria if surfaces are not dried thoroughly afterwards. Wet cleaning (wet CIP) of chambers, ducts, cyclones, fluid beds and sanitary bag filters is done at intervals with rotating spray nozzles and alkaline and acid solutions, followed by thorough drying with hot air before production restarts. Powder handling areas are kept dry, with controlled access and environmental monitoring for Salmonella and Cronobacter in plants producing infant formula ingredients. Inspection of dryers for deposits is also a fire-safety measure, as described in evaporation-drying-dairy and concentrated-dried-milks.
Three related activities show that cleaning works. Validation establishes, usually once and after changes, that a cleaning programme can reliably clean a circuit under worst-case conditions, using inspection, swabs and microbiological tests. Monitoring checks every cleaning cycle in real time: CIP control systems record temperature, flow, conductivity (concentration) and time for each step and flag deviations, so that a circuit that did not reach its set conditions is recleaned before use. Verification checks periodically that cleaning is effective, by visual inspection, ATP tests, microbiological swabs and rinse samples, and by product testing. Together they provide evidence for food safety management systems and regulators.
Visual inspection of opened equipment — tank interiors, plate packs, valve seats, gaskets, filler parts — remains essential; a surface that looks dirty is dirty, though a clean-looking surface may still carry micro-organisms or invisible films. Inspection with good lighting and, where needed, borescopes or UV torches finds residues in difficult areas. ATP bioluminescence tests detect adenosine triphosphate, present in all living cells and in food residues, by its light reaction with luciferase; a swab is read in a luminometer within a minute, giving relative light units (RLU) that are compared with pass/fail limits set by the plant for each surface. ATP tests detect organic residues rapidly but do not identify micro-organisms. Microbiological swabs and contact plates, cultured for total counts, Enterobacteriaceae, coliforms, Listeria or other targets, give organism-specific results after a day or more. Protein residue swabs give a colour change in the presence of protein. Rinse water samples tested for microbial counts, conductivity and pH show whether chemicals have been fully rinsed out. Trends in results over time, not only single values, guide improvements.
ATP and microbiological limits are set by each plant for each surface type, based on data from surfaces known to be clean and on the risk of the product. A sampling plan defines which surfaces are tested, how often, by which method, and what happens when a result fails: typically reclean and retest before use, with investigation if failures repeat. Surfaces are prioritised by risk: product-contact surfaces after the last heat treatment, such as filler nozzles, valve seats and cheese moulds, come first. Results are trended to spot gradual deterioration, such as worn gaskets or failing spray devices, before they cause product problems.
Hygienic design aims to make equipment and plant easy to clean and inspect, and to prevent contamination of product. Its principles apply to both equipment and buildings. Product-contact materials must be inert, corrosion-resistant, non-absorbent and cleanable — usually austenitic stainless steel, with suitable plastics and elastomers for seals. Surfaces must be smooth (a roughness of 0.8 µm Ra or better is commonly specified for product contact), with continuous, smooth welds. Equipment must drain completely and be self-draining; internal corners must have generous radii; there must be no crevices, threads, metal-to-metal joints or exposed fasteners in product zones; dead legs must be avoided; seals must be designed so that no gaps form; and equipment must be cleanable in place or easily dismantled for manual cleaning and inspection. Non-product surfaces should not collect dirt or water, motors and drives should be positioned so that lubricants cannot reach product, and equipment should be installed with space around it for cleaning and inspection.
Two major organisations publish hygienic design standards and guidelines used internationally. 3-A Sanitary Standards Inc., in the United States, develops standards and accepted practices for dairy and food equipment (for example for tanks, pumps, valves, heat exchangers, fittings and CIP systems), and equipment that conforms can carry the 3-A symbol after third-party verification; 3-A standards are referenced in the U.S. Grade A Pasteurized Milk Ordinance. The European Hygienic Engineering & Design Group (EHEDG), a consortium of equipment makers, food companies, research institutes and authorities, publishes guidelines on hygienic design principles, materials, welding, pipe couplings, valves, CIP, building design and other topics, and offers equipment certification based on cleanability testing. Both are widely used in specifications for new equipment. European legislation also requires food machinery to meet hygiene requirements, and ISO standards cover hygienic design of machinery. In India and elsewhere, these international guidelines are applied alongside national food safety regulations on premises and equipment.
Hygienic design extends to the building. Floors must be impervious, durable, sloped to drains and free of cracks; drains must be hygienic, trapped and easy to clean; walls and ceilings must be smooth and washable; and junctions should be coved. Air handling controls temperature, humidity and condensation and, in high-hygiene areas, supplies filtered air at positive pressure so that air flows from clean to less clean areas. Plants are divided into hygiene zones — for example raw material reception, wet processing, high-hygiene areas where product is exposed after its last heat treatment (fillers, cheese moulding, powder handling) — with controlled flows of people, materials and air between them, changing facilities, and dedicated tools and clothing for higher-risk zones. Good zoning limits the spread of Listeria and other environmental pathogens from raw to finished product areas.
Hygienic design matters at farm and village level too. Milking machines, bulk milk coolers, cans and small processing units need smooth, cleanable surfaces, good drainage and accessible parts; rubber liners and tubes must be replaced at recommended intervals because worn rubber cracks and harbours bacteria. Aluminium cans, still used in many countries, need alkaline cleaners that do not attack aluminium. Simple, robust stainless steel equipment, hot water, appropriate detergents and training in cleaning routines are often the most effective improvements in raw milk quality in smallholder dairy systems.
A biofilm is a community of micro-organisms attached to a surface and embedded in a self-produced matrix of extracellular polymeric substances (polysaccharides, proteins and DNA). Biofilm formation begins with conditioning of the surface by organic material (in dairies, milk residues), followed by attachment of cells, growth into microcolonies, maturation into a three-dimensional structure and release of cells that spread contamination. Biofilms form wherever surfaces stay wet and nutrients are present: in poorly cleaned pipes, dead legs, gaskets, valve seats, plate heat exchanger regeneration sections, evaporators, membranes, drains, floors, conveyors and filler parts. Organisms of concern include Pseudomonas and other psychrotrophic spoilage bacteria, Listeria monocytogenes (a persistent environmental pathogen in dairy plants), Bacillus and thermophilic Geobacillus and Anoxybacillus in warm sections, and Enterobacteriaceae. Cells in biofilms are much more resistant to sanitisers and heat than free cells, because the matrix limits penetration and cells within are physiologically different.
Biofilm control depends on preventing attachment and on removing biofilms fully, not merely killing surface cells. Hygienic design that eliminates dead legs, crevices and hard-to-clean areas is the first line. Effective CIP with adequate velocity and impact, alkali that removes the matrix and soil, and acid steps are essential; cleaning before soil dries and limiting production run lengths in warm sections reduce build-up. Sanitisers are effective on cleaned surfaces but much less so on established biofilms; strong oxidisers such as peracetic acid and chlorine reach biofilms better than QACs. Enzymatic cleaners targeting matrix components, and mechanical action, help remove mature biofilms. Environmental areas — drains, floors, conveyors, condensation points — need regular cleaning, keeping dry where possible, and environmental monitoring programmes that sample zones close to and further from product-contact surfaces for indicator organisms and Listeria, with corrective cleaning when results are positive. Some plants rotate sanitisers, though evidence for resistance development under good practice is limited; the decisive factor is thorough cleaning.
Pests — rodents, insects (flies, cockroaches, stored-product insects) and birds — carry pathogens, contaminate product and packaging with droppings, hair and bodies, and damage materials. Integrated pest management combines prevention with monitoring and control. Prevention means proofing buildings (sealed gaps, self-closing doors, screened windows and vents, air curtains), good housekeeping (no spilled product, waste removed promptly, tidy storage off the floor and away from walls), and control of conditions outside (vegetation cleared, waste bins closed). Monitoring uses rodent bait stations or traps at defined positions, insect light traps (electric fly killers placed away from exposed product), and pheromone traps for stored-product insects, with regular inspection and records. Control uses traps, approved baits outside production areas, and approved pesticides applied by trained personnel or contractors, never on or near exposed product. Pest control programmes are part of the prerequisite programmes audited under HACCP-based systems.
People are a major source of contamination: hands, hair, skin, clothing, footwear and illness can introduce pathogens such as Staphylococcus aureus, Salmonella, Escherichia coli and norovirus, as well as foreign bodies. Personal hygiene rules include thorough handwashing with soap and water at defined times (entering production, after using toilets, after handling waste or raw material), hand sanitising where appropriate, clean protective clothing and hairnets or caps, beard covers, dedicated footwear or boot washers and foot baths at entry to high-hygiene areas, no jewellery or loose items, no eating, drinking or smoking in production areas, covering cuts with coloured detectable dressings, and reporting illness (especially diarrhoea, vomiting or skin infections), with exclusion from food handling as required. Visitors and contractors follow the same rules. Training, supervision and well-designed facilities — handwash stations at entrances, changing rooms between zones — make compliance possible. National food safety regulations, such as the hygiene requirements in FSSAI's licensing schedule in India and the general hygiene principles of Codex, set the baseline. The food technology track's food-plant-sanitation covers these prerequisites for the wider food industry.
A student uses this subject to explain fouling and soil removal, choose detergents and sanitisers, describe and calculate CIP flows, velocities and solution make-up, and interpret ATP and swab results. It supports AIEEA-PG questions on plant hygiene, AICE Dairy Technology Unit 3 and plant training.
A hygiene or quality officer five years in runs CIP programmes, checks records and deviations, sets ATP limits and swab plans, investigates spoilage and Listeria positives, manages chemical stocks and safety, and audits pest control and personal hygiene. This subject provides the reasoning behind each programme and corrective action.
A plant head or quality director decides on CIP system design (centralised or decentralised, re-use or single-use), hygienic design specifications for new equipment and buildings, environmental monitoring strategy, and investments to save water, energy and chemicals. They answer to auditors and regulators for sanitation programmes.
A professor or research director works on fouling mechanisms, cleaning kinetics, biofilm biology and control, novel detergents and sanitisers, and sustainable cleaning. They teach and examine AICE Dairy Technology Unit 3 and advise industry on hygienic design.
This manual does not yet give: detailed CIP design calculations for complex circuits; specific detergent and sanitiser product formulations; legal limits for sanitiser concentrations and no-rinse use in each country; full EHEDG and 3-A standard text; detailed environmental monitoring plans and sampling statistics; and cleaning validation protocols. Concentrations, temperatures, times and velocities are representative values to be confirmed with suppliers and plant validation.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
These notes are free to read here, with no account.
What the Laisha app adds:
Free for ten days, then a subscription. We would rather write that here than have you find it later.