Cleaning or washing of dairy equipment implies the removal of ‘soil’ from the surface of each machine.
Sanitization (also referred to as sterilization) implies the destruction of all pathogenic and almost all non-pathogenic microorganisms from equipment surface.
Note:
‘Soil’ consists primarily of milk or milk product residues which may be more or less modified by processing treatment, or by interaction with water or cleaning materials previously used, or by dust, dirt or other foreign matter. (Soil may be one or more of the following- liquid milk films, air-dried films, heat-precipitated films, heat-hardened films, milk-stone and miscellaneous foreign matter.)
Detergents or cleaning/washing compounds are substances capable of assisting cleaning.
Sanitizers arc substances capable of destroying all pathogenic and almost all non-pathogenic micro-organisms.
Milk-stone is an accumulation of dried milk solids and salts from hard water and washing solutions. It consists largely of calcium phosphate, milk protein, precipitated, coagulated and baked-on by heat, and insoluble calcium-salts from water and washing solutions.
It has the following approximate composition:
Moisture- 2.7 to 8.7%
Fat- 3.6 to 17.7%
Protein- 4.4 to 43.8%
Ash- 42.0 to 67.3%
Importance of Cleaning Dairy Equipment:
All dairy equipment should be properly cleaned and sanitized as milk provides an excellent medium for the growth of micro-organisms. At the same time, detergents and sanitizers used for cleaning and sanitization should be so selected as not to affect the material of the equipment.
Cleaning and sanitization are complementary processes; either of them alone will not achieve the desired result, which is to leave the surfaces as free as possible from milk residues and viable organisms.
Detergents and Sanitizers Used for Cleaning Dairy Equipment:
Detergents should have the following desirable properties:
(i) Wetting and penetrating power;
(ii) Emulsifying power;
(iii) Saponifying power;
(iv) Deflocculating power;
(v) Sequestering and chelating power;
(vi) Quick and complete solubility;
(vii) Should be non-corrosive to metal surfaces;
(viii) Free rinsing;
(ix) Economical;
(x) Stability during storage;
(xi) Should be mild on hands;
(xii) Should possess germicidal action.
Note:
No single detergent possesses all the above properties. Hence two or more detergents are compounded for different operations so as to combine cleaning efficiency with safety.
Dairy detergents may be broadly classified into 4 groups:
(i) Alkalis:
Sodium hydroxide (caustic soda), sodium carbonate (washing soda), sodium phosphates, sodium bicarbonate/sesquicarbonate, sodium silicate/sulphite (as inhibitors), etc. Strong alkalis are used to saponify fat and weak alkalis to dissolve protein.
(ii) Acids:
(Mild) Phosphoric, tartaric, citric, gluconic and hydro acetylic; (Strong) Nitric. Mild acids are used for milk-stone removal; nitric acid may be used in not more than 1 per cent concentration for stainless steel surfaces.
(iii) Polyphosphates and Chelating Chemicals:
These are used together with acids or alkalis. Examples- Tetraphosphate, hexa- metaphosphate, tripolyphosphate, pyrophosphate, etc.
(iv) Surface-Active/Wetting Agents:
These are either used alone or in conjunction with acids or alkalis. Examples- Teepol, Acinol- N, Idet-10, common soaps, etc.
Note:
By careful choice from the above materials it is possible to prepare mixtures possessing the desired degree of cleaning efficiency.
Sanitizers:
These should have the following desirable properties:
(i) Nontoxic
(ii) Quick acting;
(iii) Relatively non-corrosive to hands and equipment;
(iv) Easily and quickly applied;
(v) Relatively inexpensive.
The commonly used dairy sanitizers are- steam, hot water, and chemicals (chlorine compounds, iodophor and quaternary ammonium compounds). The method of chemical sanitization broadly consists of- flushing, spraying, brushing, fogging and submersion.
Cleaning and Sanitizing Procedure:
Principles:
In the selection of any particular detergent, consideration should be given to- type of soil, quality of water supply, material of surface and the equipment to be cleaned, and method of cleaning, viz., soaking, brushing, spraying and/or recirculation. Detergents are invariably used as an aqueous solution.
In the selection of dairy sanitizers, the following considerations are kept in mind:
(a) High Temperature Sanitizing:
Main advantages are penetrating ability and quick drying of the equipment. Heat is the most reliable sanitizer, especially when both temperature and time are controlled. Thus effective sanitization can be done by steam (15 psi for 5 minutes or 0 psi for 15 minutes) or scalding water (90-95°C for 10 minutes),
(b) Low Temperature Sanitizing:
Main advantages are:
(i) Permits sanitizing immediately before equipment is used (when hot equipment will be injurious to the quality of milk or milk products);
(ii) Avoids excessive strain on equipment (such as ice-cream freezers); and
(iii) Permits flushing out of equipment immediately before use, thereby removing any possible dust that may have entered.
Generally, chlorine solution at 15-20°C containing 150 to 200 ppm available chlorine is used for a contact time of 1 to 2 minutes.
The usual procedure for cleaning and sanitization of major items of dairy equipment should consist of:
(i) Draining, to remove any residual loose milk and any other matter.
(ii) Pre-rinsing, with cold or tepid water, to remove as much milk residue and other matter as possible.
(iii) Warm to hot detergent washing with detergent solution of 0.15 to 0.60 per cent alkalinity, to remove the remaining milk- solids.
(iv) Hot water rinsing, to remove traces of detergents.
(v) Sanitizing, to destroy all pathogens and almost all non- pathogens. (Usually also done just before using the equipment.)
(vi) Draining and drying, to help prevent bacterial growth and corrosion. (Drying readily accomplished by heat and ventilation; never use a cloth or towel of any kind. Drying not necessary if equipment is to be immediately refilled with a dairy product.)
The selection and precautions in the use of detergents and sanitizers for different surface-materials of dairy equipment are given in Table 1.29.
The choice of general purpose detergents in organized dairies is given in Table 1.30.
Note:
(i) Under Indian conditions, tri-sodium silicate is usually replaced by sodium carbonate, mainly due to lower cost and easy availability of the latter. However, sodium carbonate has a lower cleaning efficiency than tri-sodium silicate.
(ii) In organized diaries, the sanitizers chosen may be steam, scalding water (90 to 95°C) or chlorine solution (150 to 200 ppm. available chlorine).
Methods of Cleaning Dairy Equipment:
These include:
(I) Hand washing,
(II) Mechanical washing and
(III) Cleaning-in-place (or in-place-cleaning).
(I) Hand Washing:
The normal cleaning and sanitization of hand-washed dairy equipment in organized dairies should be done as follows:
(i) Prepare 0.8 to 1.0 per cent of the detergent mixture (any set in Table 1.29) in tap water, so as to give a minimum alkalinity of 0.5 per cent (pH over 11.0) in a wash-up tank and maintain the temperature at about 50°C.
(ii) Thoroughly rinse the utensils with clean cold water (or tepid water in winter).
(iii) Introduce the detergent solution into the equipment (quantity of solution to be determined by requirement and experience). Thoroughly brush the equipment surface, inside and outside, with a clean can-brush.
(iv) Wash the utensil with enough fresh cold water (tepid water in winter), using a clean brush again if needed, to remove all traces of detergent.
(v) Allow the equipment to drain thoroughly and let it dry (for at least one to two hours).
(vi) Sanitize the equipment surface by steam or hot water after cleaning, and/or by rinsing with chlorine solution (200 ppm. available chlorine) just before using.
Note:
(i) Use rubber gloves to avoid skin injury from detergent action.
(ii) Two compartment wash-up tank, one for warm detergent solution and the other for hot water (with drain outlet in each tank) together with a steam jet/ chest is helpful,
(iii) Use fresh detergent and sanitizing solutions.
Bottles may be hand-washed as follows:
The operator uses either a hand-brush or a motor-driven brush, and a mild alkaline solution which will not be injurious to the hand. A three-compartment tank (with a drainage outlet for each) is helpful; table space at both ends should also be provided. Two-thirds of the first compartment is filled with water at 50-55cC containing alkali detergent (any set in Table 1.29).
The second compartment is filled similarly with water only at 50-55°C. The third compartment contains enough clean cold water, with 150 to 200 ppm. available chlorine. The (drained) bottles are put into the first compartment, and allowed to soak there for a few minutes, then brushed with a clean bottle-brush both inside and outside.
After brushing, the bottles are placed in the second compartment where they remain until all bottles in the batch are washed. Then a new batch of bottles is placed in the first compartment to be soaked; and the bottles in the second compartment, after careful emptying, are placed in the third compartment; the bottles remain here while the second batch of bottles is brushed and transferred from the first to the second compartment.
The crates are also carefully cleaned, inside and outside, and the bottles from the third compartment left upside down to be drained and dried. (As before, use rubber gloves to avoid skin injury from detergent action and as a protection against broken bottles, and use fresh detergent and sanitizing solutions when needed.)
(II) Mechanical Washing:
This consists mainly of can- and bottle-washing:
(a) Can-Washing:
Cans may be cleaned and sanitized either manually or mechanically. The mechanical can-washer may be of either the Rotary or Straight-through/Tunnel type. The rotary can washer is used in small plants; in this loading and unloading are done at the same point, and the cans move in a circle. The capacity usually ranges from 2 to 6 cans and lids per minute.
Advantages:
(i) Occupies little space;
(ii) Machine can be operated by a single worker.
The straight-through type is used in bigger plants; in this loading is done at one end and unloading at the other, and the cans move in a straight line. The capacity usually ranges from 4 to 12 cans and lids per minute.
Advantage:
Greater capacity.
The cleaning and sanitization procedure for mechanical can- washing (can and lid) consists of the following stages:
(i) Drainage stage for liquid milk residues;
(ii) Pump-fed pre-rinsing with cold or luke-warm water;
(iii) Drainage stage;
(iv) Pump-fed jetting with detergent at not less than 70°C;
(v) Drainage stage;
(vi) Rinsing stage, pump-fed or by steam and water ejector at not less than 88°C;
(vii) Final fresh water rinsing with steam and water ejector at 88 to 93°C;
(viii) Live-steam injection;
(ix) Hot-air drying at 95 to 115°C.
Note:
(i) Detergent mixture used should be suitable for the can metal; not more than 0.5 per cent alkalinity is desirable.
(ii) Sanitization with chlorine is not recommended for tinned milk cans since it attacks tin-surfaces, especially if left in contact with the tin for any length of time.
(b) Bottle-Washing:
The mechanical bottle-washer may either be a Soaker (soaking), or Hydro (jetting) or Soaker-Hydro (part soaking and part jetting). Further, it may be of the Come-back or Straight-through type; in the former, loading and unloading take place at the same end, while in the latter they are done at opposite ends.
Generally, soaker-hydro-come-back types are popular for small capacities, and straight-through-hydro types are used for larger capacities. In all machines, bottles are loaded manually or semi-automatically with manual assistance, and are discharged automatically onto one or more conveyors.
The stages of treatment in a mechanical bottle-washer are given below:
(i) Pre-rinse, using water at 32 to 38°C.
(ii) Detergent wash, usually 1-3 per cent caustic soda, together with chelating and wetting agents, given preferably in two stages at different temperatures within 60 to 75°C. Sanitizes the bottles as well.
(iii) Warm water rinse to remove all traces of detergent. Reduces bottle temperature for next stage. Water temperature varies from 25 to 45°C and is usually re-circulated.
(iv) Cold water rinse, normally re-circulated chlorinated water (containing 35 to 50 ppm. available chlorine) is used to prevent re-contamination of bottles.
(v) Draining, after the bottles come out of the machine.
Note:
Visual inspection of washed bottles is important. Under Indian conditions, this is done by workers examining each bottle through a large magnification lens. In developed dairying countries, an electronic device (Rototector) is used for detection of foreign matter in glass bottles, although it is not entirely satisfactory.
(III) Cleaning-in-Place (CIP):
Definition:
Also called In-place-cleaning (IPC). This refers to that system of cleaning and sanitization which does not require the daily dismantling of dairy equipment.
Merits:
The merits of the CIP system are:
(i) Ensures that all equipment receives uniform treatment day after day, by eliminating the human factor;
(ii) Less damage to equipment (due to daily dismantling and assembling);
(iii) Saving of (25 per cent or more) total clean-up costs and in man-hours;
(iv) Reduces possibility of contamination through human error;
(v) Improved plant utilization and appearance.
Success Factors:
The success of the CIP system depends upon:
(i) Proper selection of pipes and fittings, installation and development of circuits;
(ii) Proper temperature of cleaning solution;
(iii) Adequate velocity of cleaning solution;
(iv) Use of detergents designed specifically for re-circulation cleaning;
(v) Proper concentration of detergent solution;
(vi) Sufficient cleaning time.
Types:
The types of CIP systems are:
1. Manual Control:
In this case, the completion and setting up of the product and CIP-circuits is done manually, the valves are hand-operated and the entire process is controlled by the operator. (The use of key-pieces is recommended for safety.)
2. Automation:
Broadly speaking, the levels may be:
(i) Low Level:
Setting up of CIP and product-circuits is done automatically.
(ii) Medium Level:
Setting-up of CIP and product-circuits as well as the different types of treatment are all controlled automatically.
(iii) High Level:
Use of computer for complete control of the entire product manufacture and CIP system in large plants.
Procedure:
1. HTST Pasteurizer:
The CIP method of cleaning and sanitization of the HTST pasteurizer is as follows:
(i) Pre-rinse, with cold or tepid water till discharge water runs clear.
(ii) Acid-rinse, with acid (phosphoric) solution of 0.15 to 0.60 per cent acidity, re-circulated at 65 to 71°C for 20 to 30 minutes. (Wetting agent may be added to increase cleaning ability.)
(iii) Drain out acid solution.
(iv) Hot water rinse, with water at 65 to 71°C for 5 to 7 minutes. Rinse water drained out.
(v) Alkali rinse, with alkali detergent solution of 0.15 to 0.60 per cent alkalinity, re-circulated at 65 to 71°C for 20 to 30 minutes. (Wetting agent may be added to increase cleaning ability.)
(vi) Drain out alkali solution.
(vii) Final hot water rinse, with water at 71 to 82°C, till the whole system has been heated. Rinse water drained out. Then slightly loosen plates for drainage and drying.
Note:
(i) Nitric acid may be used with stainless steel plates.
(ii) At regular intervals, the equipment may be dismantled for thorough cleaning and inspection of all milk contact surfaces.
2. Milk Storage Tank/Milk Tankers:
The programme of cleaning and sanitization of milk storage tanks or milk tankers by the CIP method is given below.
Especially designed spray arms and nozzles (turbine or ball spray) are normally used to ensure uniform spraying of detergent and sanitizing solutions over the surface:
(i) Pre-rinse with tap water;
(ii) Drain for 3 to 5 minutes;
(iii) Hot detergent wash with sodium hydroxide solution (sodium hydroxide 90 parts, sodium thiosulfate 9 parts and wetting agent 1 part) of 0.35 to 0.50 per cent strength at 71°C for 15 to 20 minutes. Once or twice a week, an acid-alkali programme may be used. The acid may be phosphoric or nitric; this should be followed by alkali as above.
(iv) Drain for 3 to 5 minutes.
(v) Post-rinse with hot water at 65 to 70°C.
(vi) Drain for 3 to 5 minutes.
(vii) Sanitize, usually with hot water at 90°C for 2 to 3 minutes, otherwise with chlorine solution at 15 to 20°C containing 150 to 200 ppm available chlorine for a contact time of 1 to 2 minutes.
(viii) Drain for 3 to 5 minutes.
(ix) Hot air blow for 1 to 2 minutes.
Systems:
These are:
(i) Total Loss System:
In this, the detergent solutions are drained out after use.
Advantages:
(i) Less steam required for heating water;
(ii) Compact CIP unit; and
(iii) Fewer pipelines.
(ii) Saving Solutions System:
The detergent solutions are returned to their respective tanks. The strength of the solutions, however, is maintained automatically.
Advantage:
(i) Saving in detergent solutions.
Note:
The system to be used will depend largely on the hardness of water and the type of soil.