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 palleconsThe 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 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 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 character￾istics. 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