Dairy Establishment Inspection Manual – Chapter 15 – Non Thermal Processing Tasks

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1.15.0.3204 Slow Vat Records

Starter activity is a critical step to monitor in the manufacture of cultured dairy products. After inoculation of the milk with starter, acidity development (lowering of pH) should occur at an anticipated rate. If the desired pH is not achieved within the specified timeframe, action is to be taken and documented by the manufacturer. A slow vat indicates that the starter has not produced acid at the desired rate. Therefore, other competing organisms which may include pathogens, may grow and have a detrimental affect on product safety and quality.

In the case of cottage cheese, if the curd is ready for cutting in about five hours the cottage cheese is referred to as "short-set". If the curd is ready for cutting in 14 to 16 hours then the cottage cheese is referred to as "long-set". These differences in setting time must be taken into consideration when evaluating the rate of starter activity for cottage cheese.

Acidity development information is recorded in a manner that indicates acidity development for each vat. The inspector should pay particular attention to acidity development rate (required versus actual), slow vat identification and action taken on out of specification results.

1.15.0.3221 Membrane Processes

This task assesses membrane separation systems. These are membrane filtration processes that separate milk components on the basis of molecular size and/or electrical charge. While traditional or conventional filtration is typically used to separate suspended particles larger than 10µm membrane filtration separates substances of molecular sizes less that 10µm. Those species that have a molecular weight lower than the filtering threshold of the membrane will permeate the membrane.

The membrane separation techniques utilized in the dairy industry include the following:

Microfiltration (MF): Mainly used for the reduction of bacteria in skim milk, whey and brine. It is also used for defatting whey intended for whey protein concentrate (WPC) and for protein fractionation. MF membranes have a pore size of 10-1-10 -1µm. The resulting permeate of MF separation is water, minerals, lactose and some proteins.

Ultrafiltration (UF): Typically used for the concentration of milk proteins in milk and whey and for protein standardization of milk intended for cheese, yoghurt and some other products. UF membranes have a pore size of 10-2-10 -1µm. The resulting permeate (defined as the filtrate, the liquid passing through the membrane) of UF separation consists of water, minerals and lactose.

Nanofiltration (NF): Is associated with the concentration of organic components by removal of part of the monovalent ions like sodium and chlorine (partial demineralization). It is generally used for the dehydration of whey, UF permeate or retentate. NF membranes have a pore size of 10-3-10 -2µm. The resulting permeate of NF separation is water and minerals.

Reverse osmosis (RO): Consists of the concentration of solutions by the removal of water. RO is generally used for the dehydration of whey, UF permeate and condensate (defined as the retentate or the retained liquid). RO membranes have a pore size of 10-4-10 -3µm. The resulting permeate of RO separation is water.

Electrodialysis polar membranes systems: Electrodialysis is dependent on ionic mobility and preferentially removes monovalent ions. These systems consist of sets of paired membranes, each of which has whey passing on one side and water passing on the other. A direct current is applied, one membrane in each pair functioning as an anode and attracting negatively charged ions (anions), while the other functions as a cathode and attracts positively charged ions (cations). The membranes are porous to both anions and cations, which pass into the water. This type of membrane system is applicable to the production of demineralized whey powder.

Some examples of membrane systems include UF of milk prior to the manufacture of soft cheeses such as Brie and Camembert. The water, lactose and dissolved salts are forced under pressure through the membrane pores or by diffusion through the membrane. These 3 components of the milk are removed (permeate) resulting in the progressive concentration of the fat and protein (retentate). MF is also used by industry to concentrate the milk prior to cheese making where the casein micelles are concentrated and results in the removal of more whey proteins from the cheese. Use of membrane technology for cheese making has demonstrated improved yields, savings in rennet, and reductions of manufacturing time, labour, and space. A more uniform final product is also produced due to the improved drainage. Another example of membrane technology is the UF of whey where water is removed as permeate together with some of the lactose and minerals and results in the manufacture of whey protein concentrates and whey protein isolates (retentate).

Membranes are available in various forms: pipe; hollow fibre, plate and frame; and spiral wound. The material used to manufacture the membrane determines its resistance to temperature, pH and oxidizing agents and thus governs its operating conditions and cleaning techniques. Manufacturers instruction regarding the operation and cleaning of the membranes (and system) must be carefully followed to ensure maximum membrane life and efficient cleaning. Because no applications are identical, it is the responsibility of the establishment to optimize the cleaning procedures together with the membrane manufacturer and the cleaning ingredient supplier.

Generally, acid conditions are used to remove minerals and chlorinated alkali conditions with or without surfactants are used to break down protein deposits. Sometimes enzyme cleaners are also used to remove protein. For UF membranes, the chlorine (Cl) content must be maintained at the manufacturers recommended level throughout the wash cycle; Cl is added to the wash solution until no further decline in Cl level (ppm) is observed. After cleaning, the system is left full of water in general with an inhibitor for bacterial growth if the storage exceeds a critical time to prevent drying of the membranes. NF and RO membranes cannot tolerate chlorine or strong oxidizers and therefore cleaning must be accomplished with alkali, acid and surfactants. Good quality, potable water is required to prevent contamination.

Membranes are cleaned in place and thus it can be difficult to monitor efficacy of the cleaning program. Proper maintenance of the log during operation, cleaning and sanitizing cycles effectively highlights potential cleaning problems. Therefore, this log must provide a record of all the cleaning and maintenance functions performed on the units.

Membrane fouling is defined as the deposition and accumulation of feed components on the membrane surface and/or within the pores of the membrane causing an irreversible flux decline during processing. The membrane is considered to be clean when the permeate flux rate (l/m2/h) (defined as the rate of extraction of permeate measured in litres per square meter of membrane surface area per hour) and pressure (this is a combination of permeate flux rate and pressure monitoring) is in the same range as they were prior to the start of operations. Thus, the cleaning records in conjunction with flux rates are a useful tool in the determination of membrane cleanliness. A Total Plate Count of clear water drained from the system may also be used to demonstrate proper cleaning.

If a cleaning problem is evident it must be investigated, resolved and logged. As a last resort, destruction and inspection of a representative membrane element or a single tube may be required to ascertain the problem. Membrane elements selected for examination should be located at the end of the "passes". These lower flow areas have the greatest potential for product residue build-up or inadequate cleaning. Bear in mind that a decrease in flux rate is a normal event as the membranes age. However, dramatic changes indicate problems that need to be investigated and resolved.

Product Quality

The bacteriological quality of the final product has to meet the standards of the end product. In order to meet those specifications, the feed (defined as the solution to be concentrated or fractionated) can undergo a specific heat treatment or microfiltration.

1.15.0.3223 Brine Control

This task refers to brine used in cheese manufacturing.

When assessing this task the inspector observes that the manufacturer exhibits control over their brine. Factors to consider include salt concentration, microbial concentration, particulate matter and temperature. Records indicate that the manufacturer monitors the brine and appropriate action (e.g. pasteurization, filtration or changing the brine) is taken when results are unsatisfactory.

Although pasteurization or UV light treatment of brine is recommended, good records and control of the above four factors (salt concentration, microbial concentration, particulate matter, temperature) is acceptable.

If the temperature is controlled by doing the salting process in a cold room then the sanitary condition of the refrigeration unit are to be evaluated. Improper maintenance may result in the formation of condensate and mould growth which may be a source of contamination. Since pathogens have been found in drainage and condensate from cooling units it is critical that the condensate is well controlled.

1.15.0.3201 Starter Preparation

This task evaluates tanks or cans used for the preparation of bulk starter before cultured products manufacturing.

Since starter preparation involves the mixing and heating of ingredients that will be added post pasteurization to milk, it is critical that the ingredients be pasteurized under controlled conditions. The manufacturer demonstrates control over the starter preparation by defining plant specific limits for heat processing (time, temperature) of starter media. These limits should ensure that the starter media is pasteurized to eliminate pathogens. A pre-determined regular frequency, designated person to monitor and record, and action taken if product does not meet the limits are defined by the manufacturer.

Since the process of starter incubation is critical and is identical to batch pasteurization, the equipment, which includes the tank, the inlet/outlet valves and connections, the cover, the indicating thermometer, air space thermometer and recording thermometer and the records, will be assessed using the inspection criteria under Chapter 12 Batch pasteurization (1.12.01 - 1.12.05).

In cases where all the ingredients going into the starter vat have been previously pasteurized or have been shown to be phosphatase negative in the case of dry milk products (B.08.030 FDR) and the product is being hygienically handled, the mixing vats are to be rated under this task. Vats are constructed, maintained and operated in such a way as to prevent contamination of the product during the mixing process. Product accumulations are absent. All product contact surfaces shall be clean and in good condition (attention should be given to vents, agitator, inlet and outlet fittings, valves, etc.). Butterfly valves are not acceptable as they are difficult to clean. CIP supply lines and return line circuits used for CIP cleaning do not pose a cross-connection. (Refer to Appendix 10).

In order to prevent contaminating the bulk starter and cultured products it is important that these tanks be clean and in good condition (particular attention should be given to vents, agitator, valves etc.).

If cans are used to make the bulk starter, the manufacturer has controls in place, including records, to ensure adequate heat treatment (time and temperature) and maintenance and operation of the cooling tank.

When starter is conveyed to vats with pipelines; the pump, pipelines, valves and fittings are maintained and operated in a sanitary manner to prevent contamination.

When assessing this task the inspector observes that the manufacturer has control over the starter preparation process and that the equipment is constructed, maintained and operated in a sanitary manner.

1.15.0.3202 Liquid Culture Application

This task evaluates the procedures used to prepare liquid cultures and the procedures in place to clean and sanitize re-usable containers. Liquid culture application can be done by the spray bottle method or by a manual method. Liquid cultures are handled and prepared in a hygienic and sanitary manner. The manufacturer has procedures in place that control the preparation and handling of liquid cultures, and the cleaning and sanitizing of re-usable containers.

When assessing this task the inspector observes the following: liquid cultures are applied immediately after preparation; a new batch of starter is made daily and any leftover culture is discarded; all utensils and containers (e.g. spray bottle and sprayer mechanism, cloths, rubbing brushes) are washed and sanitized before use; and employees properly wash and sanitize their hands prior to starter preparation and application. The inspector reviews the records for completeness, results of testing and satisfactory follow-up and actions taken when deviations are found.

The establishment has records on file for each lot of starter used:

  1. For freeze dried cultures and bulk starter cultures, a certificate of analysis from the supplier as per 1.10.02.03 (Incoming Material) certifying no pathogens is acceptable.
  2. For the prepared liquid culture application, the manufacturer tests the prepared liquid starter culture for pathogens at a frequency sufficient to show the culture used is not a source of contamination.

1.15.0.3313 Non Food Grade Powder Handling

Non food grade powder is handled and stored in a manner that does not pose a contamination risk to dairy products. When assessing this task the inspector observes that non food grade powder is adequately packaged, clearly identified as animal feed, stored in a separate area in the warehouse and that all non food grade powder which is unsuitable for animal feed is properly stored and disposed of daily.

As a general rule, sifter "screenings" or "tailings" are considered as non food grade powder and should not be used for human food. There may be exceptions to this practice in the manufacture of certain products whereby sifter oversize material is routed to reprocessing for eventual human food use.

1.15.0.3503 Packaging Temperature

This task assesses the packaging temperature of fluid and dry milk products.

Fluid Milk Products

Psychrotrophic bacteria are the main organisms responsible for deterioration of pasteurized products. Maintaining the product at temperatures of ≤ 4°C can enhance the keeping quality of fluid milk products.

Certain filling machines may cause the product to increase in temperature. For example, there may be a temperature difference between a 250 mL carton and a 1 Litre carton of milk just after filling. It is important that packaged product be placed into a cold storage area as soon as possible after packaging to preserve the quality.

Dry Milk Products

The keeping quality of milk powders is also affected by the packaging temperature. Oxidation of the powder can be reduced by packaging the powder warm (49°C-52°C). This reduces the amount of oxygen trapped in the particles of the powder. However, warm storage temperatures affect the solubility and keeping quality properties if the powder stays at warm temperatures for too long. Therefore, it is recommended that the powder should be cooled immediately after packaging.

Because packaging is a post pasteurization step it is important to avoid contamination or subject the product to temperatures that will speed up deterioration.

When assessing this task the inspector verifies that the manufacturer has procedures in place to control the packaging temperature of fluid milk products after the filling step to minimize the deterioration of pasteurized products. These procedures include critical limits, frequency of monitoring and corrective actions for out of specification findings.

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