42 Chilled foods Table 2. 5 Indicators and spoilage organisms for milk, cream, dairy products and milk roduct Organi Maximum Soft cheese(raw milk) 102 104 Processed che < Anaerobic plate count <10 Other cheeses Coliforms Enterobacteriaceae E. coli <10 Pasteurised milk Coliforms 1 Enterobacteriaceae 000 Coliforms milk produc Enterobacteriaceae E. coli <<<≤ 0000 000 Yeasts(yogurt) 0° Milk powder Aerobic plate count <10 Product dependent E. coli 103 Source: IFST Development and use of microbiological criteria for foods. Institute of Food Science and g, London Table 2.6 Descriptions of pasteurised market milks in the UK Milk type Description Natural whole milk Milk with nothing added or removed Homogenised whole milk Homogenised milk with nothing added or removed Standard ised whole milk Milk standardised to a minimum fat content of 3.5% Standardised, homogenised whole milk Milk standardised to a minimum fat content of 3. 5% and homogenised Milk with a fat content of between 1.5 and 1. 8% Skimmed milk Milk with a fat content of less than 0.1% used in the manufacture of chilled products, particularly as a base for the production of sauces, such as bechamel, cheese and white sauces used in chilled ready-meals. In the production of pasteurised milk, raw milk is centrifugally clarified to remove insoluble particles and somatic cells. In accordance with UK dairy regulations(Anon. 1995b)it is then heat treated at not less than 711C for not less than 15 seconds. A negative phosphatase test confirms adequate heat treatment and a positive peroxidase test confirms the milk has not been overheated (taken above 80oC). Semi-skimmed and skimmed milks are produced by centrifugally separating cream using a hermetic separator, as described by
used in the manufacture of chilled products, particularly as a base for the production of sauces, such as bechamel, cheese and white sauces used in chilled ready-meals. In the production of pasteurised milk, raw milk is centrifugally clarified to remove insoluble particles and somatic cells. In accordance with UK dairy regulations (Anon. 1995b) it is then heat treated at not less than 71.1ºC for not less than 15 seconds. A negative phosphatase test confirms adequate heat treatment and a positive peroxidase test confirms the milk has not been overheated (taken above 80ºC). Semi-skimmed and skimmed milks are produced by centrifugally separating cream using a hermetic separator, as described by Table 2.5 Indicators and spoilage organisms for milk, cream, dairy products and milk powders Product Organism GMP Maximum Soft cheese (raw milk) E. coli 102 104 Processed cheese Aerobic plate count 102 105 Anaerobic plate count 10 105 Other cheeses Coliforms 102 104 Enterobacteriaceae 102 104 E. coli 10 103 Pasteurised milk Coliforms 1 102 and cream Enterobacteriaceae 1 102 Other pasteurised Coliforms 10 104 milk products Enterobacteriaceae 10 104 E. coli 10 103 Yeasts (yogurt) 10 106 Milk powders Aerobic plate count 103 Product dependent Enterobacteriaceae 102 104 E. coli 10 103 Source: IFST. 1999. Development and use of microbiological criteria for foods. Institute of Food Science and Technology, London. Table 2.6 Descriptions of pasteurised market milks in the UK Milk type Description Natural whole milk Milk with nothing added or removed Homogenised whole milk Homogenised milk with nothing added or removed Standardised whole milk Milk standardised to a minimum fat content of 3.5% Standardised, homogenised whole milk Milk standardised to a minimum fat content of 3.5% and homogenised Semi-skimmed milk Milk with a fat content of between 1.5 and 1.8% Skimmed milk Milk with a fat content of less than 0.1% 42 Chilled foods
Raw material selection: dairy ingredients 43 Early(1998a)and Brennan et al.(1990). High-pressure homogenisation(Early 998a, Brennan et al. 1990)is used to reduce the size of milkfat globules from as large as 20um down to 1-2um, thereby preventing the development of a cream layer, and the possible formation of a cream plug in glass bottles. Market milk is packaged in glass bottles, laminated paperboard cartons and plastic(high-density polyethylene) containers(Paine and Paine 1992) For industrial use pasteurised milk may be delivered by stainless-steel road tanker or in 1-tonne palletised containers(pallecons). Pasteurisation does not destroy all the microbes present in raw milk and pasteurised milk must be stored 8C to retard microbial growth. The spoilage of short shelf-life dairy products is usually due to microbial activity and post-pasteurisation contamina- tion with Gram negative psychrotrophic bacteria is often of significance(Mui 1996a). Frazier and Westhoff(1988)record the possible survival of heat- resistant lactic organisms (e. g, enterococci, Streptococcus thermophilus and lactobacilli) as well as spore-forming organisms of genuses Bacillus and Clostridium. Various quality defects are possible with pasteurised milk, including lactic souring, proteolysis (which is favoured by low-temperature example, to a protease produced by Pseudomonas flourescens, which survives pasteurisation even though the organism does not, and bitty cream caused by Bacillus cereus 2. 6.2 Cream Market cream is produced for domestic use with a range of minimum fat contents,as given in Table 2.7. In the manufacture of chilled products, cream finds application in soups, sauces and toppings. The fat content of cream for manufacturing use will be determined by various factors, e.g., whippability pumping, packaging/transport and storage limitations. Cream is an oil-in-water emulsion. The milkfat globules in unhomogenised cream range in diameter from 0. lum to 20um with an average of 3-4um. They are stabilised by the milkfat globule membrane which is comprised of phospholipids, lipoproteins, cerebrosides, proteins and other minor materials. The membrane has surface active, or surfactant properties. Most of the lipid in milkfat is triacylglycerols though small amounts of diacylglycerols and monoacylglycerols may be present Table 2.7 Minimum fat contents of market creams in the uK Cream or single cream Sterilised half cream Sterilised cream Whipping cream 35% Double cream Clotted cream 55%
Early (1998a) and Brennan et al. (1990). High-pressure homogenisation (Early 1998a, Brennan et al. 1990) is used to reduce the size of milkfat globules from as large as 20m down to 1–2m, thereby preventing the development of a cream layer, and the possible formation of a cream plug in glass bottles. Market milk is packaged in glass bottles, laminated paperboard cartons and plastic (high-density polyethylene) containers (Paine and Paine 1992). For industrial use pasteurised milk may be delivered by stainless-steel road tanker or in 1-tonne palletised containers (pallecons). Pasteurisation does not destroy all the microbes present in raw milk and pasteurised milk must be stored at 8ºC to retard microbial growth. The spoilage of short shelf-life dairy products is usually due to microbial activity and post-pasteurisation contamination with Gram negative psychrotrophic bacteria is often of significance (Muir 1996a). Frazier and Westhoff (1988) record the possible survival of heatresistant lactic organisms (e.g., enterococci, Streptococcus thermophilus and lactobacilli) as well as spore-forming organisms of genuses Bacillus and Clostridium. Various quality defects are possible with pasteurised milk, including lactic souring, proteolysis (which is favoured by low-temperature storage) due, for example, to a protease produced by Pseudomonas flourescens, which survives pasteurisation even though the organism does not, and bitty cream caused by Bacillus cereus. 2.6.2 Cream Market cream is produced for domestic use with a range of minimum fat contents, as given in Table 2.7. In the manufacture of chilled products, cream finds application in soups, sauces and toppings. The fat content of cream for manufacturing use will be determined by various factors, e.g., whippability, pumping, packaging/transport and storage limitations. Cream is an oil-in-water emulsion. The milkfat globules in unhomogenised cream range in diameter from 0.1m to 20m with an average of 3–4m. They are stabilised by the milkfat globule membrane which is comprised of phospholipids, lipoproteins, cerebrocides, proteins and other minor materials. The membrane has surface active, or surfactant properties. Most of the lipid in milkfat is triacylglycerols though small amounts of diacylglycerols and monoacylglycerols may be present. Table 2.7 Minimum fat contents of market creams in the UK Half cream 12% Cream or single cream 18% Sterilised half cream 12% Sterilised cream 23% Whipped cream 35% Whipping cream 35% Double cream 48% Clotted cream 55% Raw material selection: dairy ingredients 43
44 Chilled foods The fat soluble vitamins A, D, E and K are also present. Cream is separated from less than 72C for not less than 15 seconds (or equivale eur: hich are milk by centrifugal separation, nowadays using hermetic separators pable of producing product in excess of 70% fat. Cream is pas nd must be phosphatase negative and peroxidase positive. Half and single cream require high-pressure homogenisation to prevent phase separation and double cream may be homogenised at low pressure to increase viscosity. Whipping cream remains un-homogenised in order to assure its functionality. Clotted cream is a traditional product of the south-western counties of England. A number of methods of production exist, as described by Wilbey and Young(1989). In general they involve the heating of milk(from which clotted cream is skimmed) or 55% fat cream at moderately high temperatures (usually 75-95oC)to cause he cream to form a solid material. or 'clot' Market cream is commonly packaged in injection moulded polystyrene flat- topped round containers. Cloake and Ashton(1982)note that in the packaging of cream it is important to exclude light, which may promote auto-oxidation of the milkfat, and prevent tainting and the absorption of water. For manufacturing use, pasteurized cream is delivered in bulk stainless-steel road tankers or one-tonne pallecons. Both market and industrial pasteurised creams require chilled storage It-8oC. Rothwell et al. (1989)review a number of quality defects possible with cream. Poor microbiological quality can reduce shelf-life below 10-14 days and lipolysis, due to indigenous or microbial lipases, can result in rancidity. Physical defects concern poor viscosity, serum separation and poor whipping character 2. 6.3 Sour cream Sour cream is used both domestically and industrially, mainly in the preparation of sauces. It is produced by the lactic fermentation of single cream(not less than 18% fat)with organisms such as Lactococcus lactis subsp. lactis, Lactococcu lactis subsp. cremoris and Leuconostoc mesenteroides subsp. cremoris Fermentation causes the precipitation of casein at its isoelectric point(pH 4.6) and the formation of a set product. Market sour cream can be fermented in the pot but for industrial use agitation is necessary to produce a pumpable product which can be transported in 20kg lined buckets or one-tonne pallecons Pasteurisation of the cream prior to fermentation and the presence of lactic acid serve as preservation factors for the product, but chilled storage is also necessary and storage at-5oC will enable a 20-day shelf-life. Creme fraiche is a variant of sour cream made by culturing homogenised cream with a fat content of 18-35% with LAB such as Lactococcus lactis subsp. lactis, Lactococcus lactis subsp cremoris and Lactococcus lactis subsp. lactis var diacetylactis. Incubation at 30-32C for 5-6 hours gives a set product with a pH in the range 4.3-4.7. Stirred or set creme fraiche is supplied to the retail market to be eaten as a chilled dessert, though for industrial use in dips, sauces, desserts and ready meals, it is suppled in various forms including 20 kg pergals and one-tonne pallecons
The fat soluble vitamins A, D, E and K are also present. Cream is separated from milk by centrifugal separation, nowadays using hermetic separators which are capable of producing product in excess of 70% fat. Cream is pasteurised at not less than 72ºC for not less than 15 seconds (or equivalent) and must be phosphatase negative and peroxidase positive. Half and single cream require high-pressure homogenisation to prevent phase separation and double cream may be homogenised at low pressure to increase viscosity. Whipping cream remains un-homogenised in order to assure its functionality. Clotted cream is a traditional product of the south-western counties of England. A number of methods of production exist, as described by Wilbey and Young (1989). In general they involve the heating of milk (from which clotted cream is skimmed) or 55% fat cream at moderately high temperatures (usually 75–95ºC) to cause the cream to form a solid material, or ‘clot’. Market cream is commonly packaged in injection moulded polystyrene flattopped round containers. Cloake and Ashton (1982) note that in the packaging of cream it is important to exclude light, which may promote auto-oxidation of the milkfat, and prevent tainting and the absorption of water. For manufacturing use, pasteurized cream is delivered in bulk stainless-steel road tankers or one-tonne pallecons. Both market and industrial pasteurised creams require chilled storage at 8ºC. Rothwell et al. (1989) review a number of quality defects possible with cream. Poor microbiological quality can reduce shelf-life below 10–14 days and lipolysis, due to indigenous or microbial lipases, can result in rancidity. Physical defects concern poor viscosity, serum separation and poor whipping characteristics. 2.6.3 Sour cream Sour cream is used both domestically and industrially, mainly in the preparation of sauces. It is produced by the lactic fermentation of single cream (not less than 18% fat) with organisms such as Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris and Leuconostoc mesenteroides subsp. cremoris. Fermentation causes the precipitation of casein at its isoelectric point (pH 4.6) and the formation of a set product. Market sour cream can be fermented in the pot but for industrial use agitation is necessary to produce a pumpable product which can be transported in 20kg lined buckets or one-tonne pallecons. Pasteurisation of the cream prior to fermentation and the presence of lactic acid serve as preservation factors for the product, but chilled storage is also necessary and storage at 5ºC will enable a 20-day shelf-life. Cre`me fraıˆche is a variant of sour cream made by culturing homogenised cream with a fat content of 18–35% with LAB such as Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris and Lactococcus lactis subsp. lactis var diacetylactis. Incubation at 30–32ºC for 5–6 hours gives a set product with a pH in the range 4.3–4.7. Stirred or set cre`me fraıˆche is supplied to the retail market to be eaten as a chilled dessert, though for industrial use in dips, sauces, desserts and ready meals, it is suppled in various forms including 20 kg pergals and one-tonne pallecons. 44 Chilled foods
Raw material selection: dairy ingredients 45 2. 6.4 Butter The domestic use of butter is well known, but as an industrial ingredient used chilled foods manufacture it finds application in soups and sauces. It is a constituent of roux, along with flour, used in the preparation of sauces. Garlic butters and herb butters are used as garnishes in chilled ready meals and savour ishes, fillings for garlic bread and as toppings for cooked meats, e.g., steak, chicken and fish. The production of sweet-cream butter involves inducing phase inversion of the oil-in-water emulsion of cream to create a water-in-oil mulsion, or butter. A number of methods exist, as reviewed by Lane(1998).A commonly used method is the fritz and senn method, which involves rapidly cooling 42% fat cream to 8C and holding for 2 hours, then raising the temperature to 20-21C for 2 hours and cooling to 16C, or the churning temperature. The tempering process reduces the level of mixed fat crystals in the milkfat globules, ensuring that the high melting point triacylglycerols crystallise s pure fat crystals. This improves the spreadability of the butter, particularly when the milkfat has a low iodine value and it is hard Tempered cream is processed in a continuous buttermaker with four sections the churning cylinder beats the cream and causes the milkfat globule membrane to rupture, whereupon the fat crystals coalesce, the separation section drains buttermilk from the butter; the squeeze-drying section expels remaining buttermilk; the working section smooths the product. In the production of salted butter, salt is added in the working section. It dissolves in the aqueous, discontinuous phase of butter, and at a rate of 1. 6-2.0% results in a salt-in-water content of around 11%- sufficient to inhibit microbial activity. Microbial activity is not the sole cause of quality deterioration in butter. Evaporation causing surface colour faults and the development of oxidative rancidity causee by exposure to light are cited as possible problems(Richards 1982). Market butter is packed in tubs or foil which exclude light and possess high moisture arrier properties. Butter as an industrial ingredient is supplied in 25kg units packed in corrugated fibreboard cases lined with polyethylene film. Lactic butter may be made by the fermentation of cream with lactic acid bacteria, though the flavour of cultured butter may be replicated by the addition of certain pounds to sweet cream used for butter making(Nursten 1997). Garlic and herb butters are made by blending butter with the relevant ingredient and extruding to produce the required portion shape and size 2.6.5 Skimmed milk concentrate and skimmed milk powder Skimmed milk concentrate and skimmed milk powder find application in custards, toppings, soups, sauces, dips and desserts. Skimmed milk is the by roduct of cream separation and contains around 91% water. The skimmed milk solids are the milk proteins, lactose and minerals, with a trace of fat. Skimmed milk concentrates are made by vacuum evaporation and products of 35-40% total solids are common for bulk supply to food manufacturers. Higher solids levels give rise to problems of viscosity, age gelation and lactose crystallisation
2.6.4 Butter The domestic use of butter is well known, but as an industrial ingredient used in chilled foods manufacture it finds application in soups and sauces. It is a constituent of roux, along with flour, used in the preparation of sauces. Garlic butters and herb butters are used as garnishes in chilled ready meals and savoury dishes, fillings for garlic bread and as toppings for cooked meats, e.g., steak, chicken and fish. The production of sweet-cream butter involves inducing phase inversion of the oil-in-water emulsion of cream to create a water-in-oil emulsion, or butter. A number of methods exist, as reviewed by Lane (1998). A commonly used method is the Fritz and Senn method, which involves rapidly cooling 42% fat cream to 8ºC and holding for 2 hours, then raising the temperature to 20–21ºC for 2 hours and cooling to 16ºC, or the churning temperature. The tempering process reduces the level of mixed fat crystals in the milkfat globules, ensuring that the high melting point triacylglycerols crystallise as pure fat crystals. This improves the spreadability of the butter, particularly when the milkfat has a low iodine value and it is hard. Tempered cream is processed in a continuous buttermaker with four sections: the churning cylinder beats the cream and causes the milkfat globule membrane to rupture, whereupon the fat crystals coalesce; the separation section drains buttermilk from the butter; the squeeze-drying section expels remaining buttermilk; the working section smooths the product. In the production of salted butter, salt is added in the working section. It dissolves in the aqueous, or discontinuous phase of butter, and at a rate of 1.6–2.0% results in a salt-in-water content of around 11% – sufficient to inhibit microbial activity. Microbial activity is not the sole cause of quality deterioration in butter. Evaporation causing surface colour faults and the development of oxidative rancidity caused by exposure to light are cited as possible problems (Richards 1982). Market butter is packed in tubs or foil which exclude light and possess high moisture barrier properties. Butter as an industrial ingredient is supplied in 25kg units, packed in corrugated fibreboard cases lined with polyethylene film. Lactic butter may be made by the fermentation of cream with lactic acid bacteria, though the flavour of cultured butter may be replicated by the addition of certain compounds to sweet cream used for butter making (Nursten 1997). Garlic and herb butters are made by blending butter with the relevant ingredient and extruding to produce the required portion shape and size. 2.6.5 Skimmed milk concentrate and skimmed milk powder Skimmed milk concentrate and skimmed milk powder find application in custards, toppings, soups, sauces, dips and desserts. Skimmed milk is the byproduct of cream separation and contains around 91% water. The skimmed milk solids are the milk proteins, lactose and minerals, with a trace of fat. Skimmed milk concentrates are made by vacuum evaporation and products of 35–40% total solids are common for bulk supply to food manufacturers. Higher solids levels give rise to problems of viscosity, age gelation and lactose crystallisation. Raw material selection: dairy ingredients 45