10 Chilled and frozen storage Theoretically, there are clear differences between the environmental con- ditions required for cooling, which is a heat removal/'temperature reduction process, and those required for storage where the aim is to maintain a set product temperature. However, in many air-based systems, cooling and storage take place in the same chamber and even where two separate facil- ities are used, in many cases not all the required heat is removed in the cooling phase. This failure to remove the required heat can be due to a number of causes insufficient time allowed insufficient refrigeration capacity to cater for high initial product load overloading variability in size of products incorrect environmental conditions. Extensive data are available on the optimum storage conditions and attainable chilled and frozen storage lives for many products(IIr, 2000; IIR, 1986; ASHRAE, 1998) torage life terms There are a wide range of rather confusing definitions used to define sto life. The EC directive( Commission of the European Community states simply that frozen storage must preserve the intrinsic characteristics of the food. Although this is probably every food technologists aim, many different criteria can be used to measure these characteristics. The Iir
10 Chilled and frozen storage Theoretically, there are clear differences between the environmental conditions required for cooling, which is a heat removal/temperature reduction process, and those required for storage where the aim is to maintain a set product temperature. However, in many air-based systems, cooling and storage take place in the same chamber and even where two separate facilities are used, in many cases not all the required heat is removed in the cooling phase. This failure to remove the required heat can be due to a number of causes: • insufficient time allowed • insufficient refrigeration capacity to cater for high initial product load • overloading • variability in size of products • incorrect environmental conditions. Extensive data are available on the optimum storage conditions and attainable chilled and frozen storage lives for many products (IIR, 2000; IIR, 1986; ASHRAE, 1998). 10.1 Storage life terms There are a wide range of rather confusing definitions used to define storage life. The EC directive (Commission of the European Community, 1989) states simply that frozen storage must ‘preserve the intrinsic characteristics’ of the food. Although this is probably every food technologist’s aim, many different criteria can be used to measure these characteristics. The IIR
208 Meat refrigeration recommendations(1986) define frozen storage life as being" the physical and biochemical reactions which take place in frozen food products leading to a gradual, cumulative and irreversible reduction in product quality such that after a period of time the product is no longer suitable for consump- tion or the intended process'. This definition tends to indicate that a frozen product may deteriorate until it is in a very poor condition before storage life ends, and so rather contradicts the ec definition. IIR(1986)recommendations also include the term of practical storage life(PSL). PSL is defined as 'the period of frozen storage after freezing during which the product retains its characteristic properties and remains table for consumption or the intended process. Bogh-Sprensen(1984) describes PSl as the time the product can be stored and still be acceptable to the consumer. Both of these definitions of PsL depend on the use of sensory panels, leading to the difficulty of defining acceptability and select ing a panel that represents consumers Another term referred to is high quality life(HQL). This concept wa developed in the 'Albany'experiments started in 1948. HQL is'the time elapsed between freezing of an initially high quality product and the moment when, by sensory assessment, a statistically significant difference P<0.01) from the initial high quality (immediately after freezing)can be established(IIR, 1986). The control is stored at"C or colder to mini- mise quality changes. Although well suited to research work, some draw backs have been noted The actual definition of storage life and the way it is measured has the ere fore been widely left to the assessment of individual authors. In some cases sensory assessment has been coupled with chemical or instrumental tests, which although probably more repeatable than human judgements, are again used at the author's discretion. Food technologists have no standard way of estimating shelf-life. Researchers have used many different methods of assessing samples, often with little thought of the initial quality, pre- freezing treatment or size of their samples. This deficiency has led to poor recommendations that can be misleading to users of the data The IIr(2000)definition of chilled storage is very similar to that of frozen storage life. Expected or practical storage life is'the greatest length of time for which the bulk of the produce may be stored either with imum commercially acceptable loss of quality and nutritive value or with maximum acceptable wastage by spoilage 10.2 Chilled storage Extensive data are available on the attainable chilled storage lives for many products (Table 10. 1). In most cases the limiting factors that control the chilled storage life of meat are based on bacterial growth. Off odours and slime caused by microorganisms are detected when populations reach ca
recommendations (1986) define frozen storage life as being ‘the physical and biochemical reactions which take place in frozen food products leading to a gradual, cumulative and irreversible reduction in product quality such that after a period of time the product is no longer suitable for consumption or the intended process’. This definition tends to indicate that a frozen product may deteriorate until it is in a very poor condition before storage life ends, and so rather contradicts the EC definition. IIR (1986) recommendations also include the term of practical storage life (PSL). PSL is defined as ‘the period of frozen storage after freezing during which the product retains its characteristic properties and remains suitable for consumption or the intended process’. Bøgh-Sørensen (1984) describes PSL as ‘the time the product can be stored and still be acceptable to the consumer’. Both of these definitions of PSL depend on the use of sensory panels, leading to the difficulty of defining acceptability and selecting a panel that represents consumers. Another term referred to is high quality life (HQL). This concept was developed in the ‘Albany’ experiments started in 1948. HQL is ‘the time elapsed between freezing of an initially high quality product and the moment when, by sensory assessment, a statistically significant difference (P < 0.01) from the initial high quality (immediately after freezing) can be established’ (IIR, 1986). The control is stored at -40 °C or colder to minimise quality changes. Although well suited to research work, some drawbacks have been noted. The actual definition of storage life and the way it is measured has therefore been widely left to the assessment of individual authors. In some cases sensory assessment has been coupled with chemical or instrumental tests, which although probably more repeatable than human judgements, are again used at the author’s discretion. Food technologists have no standard way of estimating shelf-life. Researchers have used many different methods of assessing samples, often with little thought of the initial quality, prefreezing treatment or size of their samples. This deficiency has led to poor conclusions and recommendations that can be misleading to users of the data. The IIR (2000) definition of chilled storage is very similar to that of frozen storage life. Expected or practical storage life is ‘the greatest length of time for which the bulk of the produce may be stored either with maximum commercially acceptable loss of quality and nutritive value or with maximum acceptable wastage by spoilage’. 10.2 Chilled storage Extensive data are available on the attainable chilled storage lives for many products (Table 10.1). In most cases the limiting factors that control the chilled storage life of meat are based on bacterial growth. ‘Off’ odours and slime caused by microorganisms are detected when populations reach ca. 208 Meat refrigeration
Chilled and frozen storage 209 Table 10.1 Chilled storage times Storage time(days(sd)in temperature range(C) -4.1to-1.1-1-22.1-5.152-8.2 45(6)15 Beef 40(26)34(32)10 Cold meat Lamb 41(46)28(34 Meals 15(18) Poultry 32(18) 12(11)7(3) Rabbit 13(6 Sausage 80(43)21(16)36(28)24(10) e 10(6)49 16 口 Odour 86420 Storage temperature( C) Fig 10.1 Time( days) for odour or slime to be detected on beef sides with average initial contamination stored at different temperatures(source: Ingram and Roberts, rate of microbial growth and hence the shelf-life of chilled meal ting the 10-10 organisms cm. Temperature is the principal factor affec 10.2.1 Unwrapped meat Temperature is the prime factor controlling storage life of wrapped meat Odour and slime will be apparent after ca. 14.5 and 20 days, respectively, with beef sides stored at 0C(Fig. 10.1). At 5C, the respective times are significantly reduced to 8 and 13 days
107 –108 organisms cm-2 . Temperature is the principal factor affecting the rate of microbial growth and hence the shelf-life of chilled meat. 10.2.1 Unwrapped meat Temperature is the prime factor controlling storage life of wrapped meat. Odour and slime will be apparent after ca. 14.5 and 20 days, respectively, with beef sides stored at 0°C (Fig. 10.1). At 5°C, the respective times are significantly reduced to 8 and 13 days. Chilled and frozen storage 209 Table 10.1 Chilled storage times Storage time (days (sd)) in temperature range (°C) -4.1 to -1.1 -1–2 2.1–5.1 5.2–8.2 Bacon 45 (6) 15 (3) 42 (20) Beef 40 (26) 34 (32) 10 (8) 9 (9) Cold meat 14 (9) 20 (17) 8 (0) Lamb 55 (20) 41 (46) 28 (34) Meals 34 (18) 15 (7) 21 (38) 18 (4) Offal 7 7 (6) 14 (7) Pork 50 (58) 22 (30) 16 (16) 15 (18) Poultry 32 (18) 17 (10) 12 (11) 7 (3) Rabbit 9 (7) 13 (6) Sausage 80 (43) 21 (16) 36 (28) 24 (10) Veal 21 10 (6) 49 49 Source: IIR, 2000. 20 18 16 14 12 10 8 6 4 2 0 Time (days) 20 10 5 0 Storage temperature (°C) Odour Slime Fig. 10.1 Time (days) for odour or slime to be detected on beef sides with average initial contamination stored at different temperatures (source: Ingram and Roberts, 1976)
210 Meat refrigeration Table 10.2 General levels of microbiological contamination reported on meat carcasses throughout the world Type of ry APC*K Reference (logo org 19-3.7 Ingram and Roberts(1976) Ingram and roberts (1976) New zealand Ingram and Roberts (1976) New Zealand Norway 1.3-3.9 chanson et aL. (1983) Roberts et al. (1984) 4-3.8 Hudson et al. (198 New zealand 04-3.3 Bell et al.(1993) australia Anon(1997) Canad 1.5-3.2 Gill et al.(1998b) Hinton et al.(1998) Lamb/ New Zealand Newton et al.(1978 Prieto et al. (1991) New Zealand 2.3-4.1 Bell et al. (1993) New Zealand Biss and Hathaway(1995) australia 2.5-3.3 Ingram and Roberts(1976) Hanson et al.(1983) 16-3.8 Christensen and Sorensen(1991) 4.3-5.0 Barbuti et aL. (1992) 4 Values are not directly comparable since different sampling techniques and incubation temperatures have been used The initial level of bacterial contamination will of course affect the storage life. Over 40 years ago Ayres(1955), in his comprehensive review of microbiological contamination in slaughtering, concluded that an aerobic population of 4.0-5.0logio cfucm- and an anaerobic population of between 3.7 and 4.7" would be reasonable for wholesale cuts of meat Surveys from the mid-1970s have shown that in general levels of between 1 and logo cfug- can be expected on red meat carcasses(Table 10.2) Specific surfaces of the carcass can have very high levels of initial con- tamination Beef subcutaneous fat has been shown to have a high initial microbial load and a capacity to support extensive bacterial growth(Lasta et aL., 1995). Initial values of total viable counts increase from an initial value of 5.4 to 10.0logo cfucm" after 11 days in a moist environment at 5C (Fig. 10.2). No noticeable deterioration in appearance of the sample was found after 14 days which was worrying. This type of material is often incor orated in manufactured products or could provide a cross contamination source The above results were obtained on the surface of samples stored in air nearly saturated with water vapour. There is much industrial belief that the surface of meat carcasses must be allowed to dry or storage life will be com-
The initial level of bacterial contamination will of course affect the storage life. Over 40 years ago Ayres (1955), in his comprehensive review of microbiological contamination in slaughtering, concluded that an aerobic population of 4.0–5.0 log10 cfucm-2 and an anaerobic population of between 3.7 and 4.7 log10 cfug-1 would be reasonable for wholesale cuts of meat. Surveys from the mid-1970s have shown that in general levels of between 1 and 4 log10 cfu g-1 can be expected on red meat carcasses (Table 10.2). Specific surfaces of the carcass can have very high levels of initial contamination. Beef subcutaneous fat has been shown to have a high initial microbial load and a capacity to support extensive bacterial growth (Lasta et al., 1995). Initial values of total viable counts increase from an initial value of 5.4 to 10.0 log10 cfu cm-2 after 11 days in a moist environment at 5°C (Fig. 10.2). No noticeable deterioration in appearance of the sample was found after 14 days which was worrying.This type of material is often incorporated in manufactured products or could provide a cross contamination source. The above results were obtained on the surface of samples stored in air nearly saturated with water vapour. There is much industrial belief that the surface of meat carcasses must be allowed to dry or storage life will be com- 210 Meat refrigeration Table 10.2 General levels of microbiological contamination reported on meat carcasses throughout the world Type of Country APC* Reference meat (log10 organism) Beef UK 1.9–3.7 Ingram and Roberts (1976) Sweden 2.2–3.4 Ingram and Roberts (1976) New Zealand 1.3–4.3 Ingram and Roberts (1976) New Zealand 1.4–2.2 Newton et al. (1978) Norway 1.3–3.9 Johanson et al. (1983) EU 2.3–3.9 Roberts et al. (1984) UK 3.4–3.8 Hudson et al. (1987) New Zealand 0.4–3.3 Bell et al. (1993) Australia 3.2 Anon (1997) Canada 1.5–3.2 Gill et al. (1998b) UK 2.45–4.29 Hinton et al. (1998) Lamb/ New Zealand 2.5–2.9 Newton et al. (1978) sheep Spain 4.96 Prieto et al. (1991) New Zealand 2.3–4.1 Bell et al. (1993) New Zealand 3.9–4.6 Biss and Hathaway (1995) Australia 3.9 Anon (1997) Pig UK 2.5–3.3 Ingram and Roberts (1976) Norway 2.6–3.9 Johanson et al. (1983) Denmark 1.6–3.8 Christensen and Sørensen (1991) Italy 4.3–5.0 Barbuti et al. (1992) * Values are not directly comparable since different sampling techniques and incubation temperatures have been used
Chilled and frozen storage 211 □ Pseudomonas wE8 4 2 Fig. 10.2 Growth of bacteria on naturally contaminated beef-brisket fat stored at 5C(source: Lasta et aL., 1995) promised. There appear to be no clear scientific studies that store carcasses under a range of industrial conditions to prove or disprove this belief. Iny tigations on pork chilling( Greer and Dilts, 1988) have shown that while conventional chilling significantly reduces the level of mesophilic bacteria, boning there was no signe y chilling. However, this work found that after duced by either treatment. Other studies found no difference in off-odours during storage and retail display of pork chops from pork cooled under either of the two methods, though the appearance of the spray chilled samples deteriorated slightly faster than those treated conventionally (Jeremiah and Jones, 1989) 10.2.2 Wrapped meat TTT(time-temperature-tolerance )and PPP(product-process-packaging) factors significantly influence the storage life of chilled meat (Bogh Sorensen et al., 1986). In some cases the initial processing stage can hay more effect than the subsequent storage conditions. After manufacture, sausages made from hot-boned pork had higher total bacterial counts (4.1 loglo cfug")than those from cold-boned meat(2.7 logo cfu 1g")(Bentley et al., 1987). When they were stored at 4 or -1C for 28 days there were no differences between counts at the two temperatures. However, the counts were very high, 8.7 and 8.9 logo cfug", in both cases. In vacuum-packaged primals, Egan et al.(1986)have shown that the tem perature of storage and ph determines both the storage life and the nature of the changes during storage(Table 10.3) Flora on high pH (>6.0) beef cuts, vacuum packaged in polyvinylidene chloride(PVDC) reached maximum levels in 6 weeks at 1C compared
promised. There appear to be no clear scientific studies that store carcasses under a range of industrial conditions to prove or disprove this belief. Investigations on pork chilling (Greer and Dilts, 1988) have shown that while conventional chilling significantly reduces the level of mesophilic bacteria, this does not occur when spray chilling. However, this work found that after boning there was no significant difference in bacterial counts on loins produced by either treatment. Other studies found no difference in off-odours during storage and retail display of pork chops from pork cooled under either of the two methods, though the appearance of the spray chilled samples deteriorated slightly faster than those treated conventionally (Jeremiah and Jones, 1989). 10.2.2 Wrapped meat TTT (time–temperature–tolerance) and PPP (product–process–packaging) factors significantly influence the storage life of chilled meat (BøghSørensen et al., 1986). In some cases the initial processing stage can have more effect than the subsequent storage conditions. After manufacture, sausages made from hot-boned pork had higher total bacterial counts (4.1 log10 cfu g-1 ) than those from cold-boned meat (2.7 log10 cfu g-1 ) (Bentley et al., 1987). When they were stored at 4 or -1 °C for 28 days there were no differences between counts at the two temperatures. However, the counts were very high, 8.7 and 8.9 log10 cfug-1 , in both cases. In vacuum-packaged primals, Egan et al. (1986) have shown that the temperature of storage and pH determines both the storage life and the nature of the changes during storage (Table 10.3). Flora on high pH (>6.0) beef cuts, vacuum packaged in polyvinylidene chloride (PVDC) reached maximum levels in 6 weeks at 1°C compared Chilled and frozen storage 211 10 8 6 4 2 0 0 2 4 7 9 11 14 Days at 5 °C Log cfu cm–2 Total Gram negs Pseudomonas Fig. 10.2 Growth of bacteria on naturally contaminated beef-brisket fat stored at 5 °C (source: Lasta et al., 1995)