Weight Loss During Chilling and Freezing of Meat
By: Eben van Tonder
10 March 2019
FREEZING AND STORAGE OF MEAT
Dehydration of meat during storage under refrigerated conditions contributes to a loss in quality and a significant economic loss due to the loss in weight. The reason for dehydration is due to the fact that the surface of the meat is “exposed to heat and mass transfer exchange with the environment. The difference between the water vapour pressure on food surface and that in the air bulk is the driving force for dehydration.” (Campanone et al, 2002)
Temperature and Weight
Campanone et al (2002) report that temperature and weight followed a similar behaviour with time. (see Graph 1)
Internal Product Temperature
Campanone et al (2002) describe the results as shown in graph 1 as follows for internal product temperature. “The internal product temperature curve presented three slope changes. The first coincided with the beginning of surface freezing, the second occurred at the end of the change of state whereas the last took place when the internal product temperature approaches the air temperature.”
Campanone et al (2002) describe the results as shown in graph 1 as follows for weight loss. “The weight loss curve displayed only one pronounced slope change when the temperature of the sample reached the air temperature.
Bustabad (1999) did a very useful study. She chilled and then froze beef and pork, quarters or sides and stored it for six months, in stores with different cooling systems, different temperatures and in some cases, with covering. “Some meat was frozen without a previous chilling. The weight loss was determined and the results were statistically analysed by a multiple step-by-step regression.” She analized weight and quality deterioration. The results of weight loss are reported in Table 1 below. The air velocity was between 0.8 and 3 m/s and the temperatures between 20°C and 30°C.
“It is well known that evaporation of moisture from the outer layers of food in frozen storage results in significant weight losses (Rutov, 1955). The percentage weight losses for a six-month period and their monthly averages obtained are presented in Table 2.
Carcass Size, Fat and Rind
Bustabad (1999) found that “forward quarters presented the greatest losses as the surface/volume ratio is greater, as also reported by Bailey (1971). Pork sides have lesser losses than beef due to their natural fat covering and skin; Cutting and Malton (1973) also reached similar conclusions.
Boxing and Wrapping/ Bagging
The least losses were reported in the Bustabad study (1999) “by freezing boneless beef in boxes, and are minimal when the meat is wrapped in polyethylene bags. This was also proven by Washburn (1985). It is necessary, however, to consider the effects of packaging on prolonging the freezing time (Cutting, 1974).”
The effect of packing on weight losses is marked, decreasing it by more than 50%. Bailey (1976) recommended the use of polyethylene less than 0.05 mm thick, and in this case we used a 0.06 mm thick one. Plank and Kallert (1916) showed weight losses, for six-month storage, in beef quarters and pork sides with a weight similar to the samples used in this work when the temperature was 10°C. In both cases, the reported losses are greater despite being at a storage temperature of 13°C. It would be expected to be smaller from the work of Cutting and Malton (1974) on the relationship between the rate moisture evaporation and storage temperature.” (Bustabad, 1999)
Table 3 shows weiht loss under industrial conditions in the Bustabad study. Cardboard boxes are recommended for storage because the shape stacks well and it reduces the weight loss (Stephen, Creed & Bailey, 1982).” (Bustabad, 1999)
“The hot pieces that were frozen had similar losses to the rest of the samples. In general, the results show greater losses than those reported by other authors such as Lorentzen and Rosvik (1959) and Manev (1983). This is influenced by the freezing conditions that in most of the cases are more severe and besides the quality of carcasses and their fat layers are greater (Cutting, 1974, 1976).” (Bustabad, 1999)
Freezing Temperatures – Colder is Better and Wrapping is Best
Bustabad (1999) reports that an experiment (Experiment 3) was carried out under industrial conditions, “where the studied storage temperatures were 13°C and 18°C, in air-cooled stores. The resulting weight losses are included in Table 4.” The losses at 13°C are far greater than those of pieces stored at 18°C. If we compared the non wrapped and wrapped (in polyethylene) meat cuts, it can be seen that the effect of temperature decreased significantly when wrapped. (Bustabad, 1999)
“Packing resulted in a highly significant effect; the greatest value in Experiment 3 indicates that it has a further importance if the pieces are hung on hooks. The coefficients related to the quarter factor indicate that the greatest weight losses occur in forward quarters and that stack storage diminishes this effect. This again corresponds to the observations of Bailey (1971) and the higher surface to volume ratio of such quarters. Non-chilled frozen quarters show greater losses during storage, and this is most significant in the case of hanging storage.”
The lesser weight losses occur at lower temperature storage, which is related to the difference between vapour pressure at the surface of the meat and surrounding air (Jasper & Placzek, 1978). In the study of effects of interactions on weight losses, the use of packing diminishes them in forward quarters and its use has a greater importance if storage time and temperature are higher, and is more significant in chambers with greater air speed and hanging storage.” (Bustabad, 1999)
“Results obtained in this experiment can be compared to those by Sheffer and Rutov (1970). The ones included in Table 4 are greater. If we take results from polyethylene packing, the values of losses would be closer to those reported in the literature. Indeed, none of these references specify the weight of pieces used in the experiment.” (Bustabad, 1999)
Increasing Airspeed by 1m/s
“Experiment 4, carried out in a chamber with an airspeed of 0.5 m/s and reported in Table 5 allows a comparison between the weight losses obtained at 18°C. The effect of the increase in airspeed is noticeable in increasing weight losses, which is not observed in those pieces packed in polyethylene.” (Bustabad, 1999)
Food Science Australia writes there is another problem with increased air velocity. “Higher air velocities enable more rapid chilling, but the fan power requirements increase by the cube of the air velocity. In most practical situations increasing the air velocity above 1 m/s cannot be justified by the small increase in cooling rate.” (Food Science Australia)
A very good suggestion on how to handle this predicated on the way that cooling takes place. “At the beginning, moisture loss is caused by liquid water evaporation during refrigeration. Then, as the surface becomes frozen, weight losses are due to ice sublimation. At both stages, the driving forces are the vapour pressure and temperature differences between food surface and the bulk air. As the sample approaches the external temperature, the temperature driving force disappears, so only the vapour pressure difference remains and the weight loss rate decreases.” (Campanone et al, 2002) Initial cooling happens due to the difference in temperature between the meat surface and the air temperature. As the surface temperature reaches the air temperature after 8 – 10 hours of cooling, the rate of cooling becomes more dependant on the thermal conductivity of the meat and not the rate of transfer of heat from the meat surface to the air. It will, therefore, make sense that the air velocity now be reduced to below 0.5m/s after 8 – 10 hours of beef chilling. Such a reduction will have little effect on the cooling rate but will have economic benefits by reducing weight loss and fan power consumption. (Food Science Australia)
“This is particularly important if the room is also required to operate as a storage chiller over weekends or longer periods.” (Food Science Australia)
Storage Time and Weight Loss
“In Table 6, regression coefficients for beef show the significance of the main effects (time, packing, temperature, previously chilled or non-chilled freezing and type of quarter) and are listed together with their interactions in each experiment. The corresponding constants of the regression equation, their correlation coefficients and the F-value in the regression analysis are also listed. Results show that the longer the storage time, the greater the losses due to evaporation. This effect has a greater influence in the case where the chamber has a greater airspeed (Experiment 4).”(Bustabad, 1999)
Combined effect of Time, Packaging, Temperature and Non-Chilled Freezing
“In the study on pork, the main effects considered were time, packing, temperature, non-chilled freezing and their interactions. Results are reported in Table 7. Regression coefficients for factors such as time, packing and temperature were highly significant. The highest times and greater temperatures have the greatest weight losses.” (Bustabad, 1999)
“The use of packing diminishes losses. The highest value in Experiment 1 is related to storage conditions, higher temperatures (13°C) and forced air circulation. When comparing with the coefficients obtained for beef, it can be observed that packing is less important in the case of pork weight losses.
Coefficients for the effect of non-chilled or previously chilled freezing indicate that weight losses during storage are greater for non-chilled sides. The most important result in the study of interactions was that the use of packaging is more important if time and storage temperatures are higher. The adequacy of the models obtained is evident by observing the values of multiple correlation coefficients in each case and can also be checked by the analysis of residuals.” (Bustabad, 1999)
Many equipment suppliers have recently emerged who offer solutions based on the impact of Relative Humidity on weight loss in carcass chillers. “Relative humidity (RH) has a greater effect on weight loss than either air temperature or air velocity. Experimental work demonstrated that decreasing the humidity from 95% to 80% increased weight loss for beef sides by nearly 0.5% over an 18-hour chill. Therefore, for carcass chilling, the aim should be to keep the humidity as high as possible (above 90%) throughout the chilling cycle, particularly if carcasses are held for extended periods.
The cause of low RH in a chiller is usually related to the original plant design and the manner in which it is operated. If the evaporator is undersized, it may be necessary to use a low evaporating temperature in order to achieve the desired rate of heat removal. This will create a large difference between the evaporator coil temperature and the temperature of the air. The larger the temperature difference, the more moisture will be drawn from the air in the form of condensation on the coil. Undersized evaporators are usually a result of attempts to minimise capital costs in the original chiller construction.
The design and surface area of the finned coil evaporator will have a major influence on the chiller RH and, as a result, on the evaporative weight loss. Design of the finned coil is a complex subject with factors such as tube diameter and configuration, coil depth, surface area, refrigerant flow path, fin spacing, all having some effect on performance. The combination of the depth of the coil and the face area is one of the most important considerations. A shallow coil of adequate surface area will provide the best performance with respect to minimising weight loss.
Best results are achieved with coolers that are designed for a 3.0 to 3.5ºC difference between the refrigerant evaporating temperature and the entering air temperature, and an air temperature reduction through the coil of 0.5 to 0.8ºC.
The heat load in the room will be much higher at the beginning of the chilling cycle. The peak load can be more than three times the average heat load; therefore, during the latter part of the chilling cycle, the evaporators will be oversized. It is useful then to have the facility to modulate the refrigerant suction temperature through back-pressure control so that the air cooler operates at the highest possible suction temperature for the load. This will minimise the temperature difference between the coil and the air, resulting in the highest RH.
“Spray chilling of beef sides is used extensively in the United States and in some Australian plants. A major aim is the reduction of evaporative weight loss. A variety of spraying regimes has been used with longer periods of spraying resulting in less weight loss. Australian regulations require that no carcass shall have gained weight after chilling. Spray chilling for the first 6 to 10 hours of a 20-hour chilling cycle will result in an average carcass weight loss of 0.2 to 0.4% with no sides gaining weight.
Slightly faster cooling rates have been reported with spray chilling for the surface and the thinner sections of beef carcases when compared with conventional chilling. Researchers report that sides held for a further six days after overnight spray chilling lost less weight (3.2%) compared with conventional chilling (4.2%). Research also indicates that there is no significant difference between conventional and spray chilling in the quantity of weep in vacuum bags and the losses during retail display and cooking.” (Food Science Australia)
Averages to use in Planning
It is good to know what effects weight loss and a loss in meat quality. Many of the factors we have control over, but over many factors, we will have little control. What are some averages that we can use in our planning or use as a general guide?
Here is a very helpful table from Food Science Australia, reporting on US figures.
“The results of the sensory assessment do not indicate quality losses which could be organoleptically detected. Moreover, rancidity was not found in any case, and there were not significant differences among the different storage conditions with regard to colour, flavour, and odour.
When comparing the toughness between non-chilled meats and previously chilled frozen meat, the toughest was non-chilled frozen beef. This can be explained by the phenomenon known as cold shortening (Taylor, Chrystall & Rhodes, 1972; Calvello, 1981; Mackie, 1993). In the case of pork, this phenomenon was not recorded due to the fast decrease in pH after slaughter compared to beef (Bendall, 1972).
Different storage temperatures, use or not of wrapper and non-chilled or pre-chilled meat were compared. There were no significant differences between different storage conditions with regard to colour, taste and codour in any experiment.
Moreover, rancidity was not found to be significant in any case although it is known that one of the fundamental alterations in stored meat at temperatures below the freezing point is rancidity and it is more frequent in pork meat owing to larger susceptibility of their oils.
When comparing toughness between non-chilled meats and previously chilled frozen meat, it could be observed for beef in Experiment 1 that in the second month 14 judges found toughness in the frozen meat without previous chilling. Nevertheless, this was not significant because a minimum of 18 concurring scores are necessary for significance.
The judges preferred the toughness of previously chilled frozen meat at 2 and 4 months storage. After 6 months, 19 judges detected toughness in the non-chilled frozen meat, this result being significant. Likewise in Experiment 3, in the 4th Test, the results of comparing toughness were the following: 19 of the 20 judges detected the largest toughness in non-chilled meat freezing.
This sensory analysis results can be explained by the phenomenon known as cold shortening (Taylor et al., 1972; Calvello, 1981; Mackie, 1993; Bailey, 1976) thus limiting the use of rapidly lowering temperature in order to minimize weight loss. These results indicated that the conditions for this phenomenon to occur were present. To avoid cold shortening, the meat should not reach 10°C before pH falls to 6.2, after slaughter.” (Bustabad, 1999)
Van der Wal et al. (1995) reported that “losses in carcass weight, 24 h after conventional and forced chilling at -5°C, were about 2%. After ‘ultra’ rapid chilling (-30°C) the losses were reduced to 1.3% when air velocity was increased to 4 m/s. Meat quality of the longissimus lumborum muscle was not significantly affected by the various chilling regimes except for the variables related to tenderness. The Warner-Bratzler shear forces were higher (P < 0·05) together with shorter sarcomere lengths (P < 0·10) after ‘ultra’ rapid chilling at a high (4 m/s) air velocity, indicating an increased risk of cold shortening,” thus confirming the conclusion of Bustabad.
“When comparing toughness between non-chilled meats and previously chilled frozen meats, in the case of pork meat, significant differences were not found. These results agreed with most of the previous investigators, who have reported that cold shortening was not recorded in pork meat due to the fast decrease in pH after slaughter compared to beef (Bendall, 1972).
In the sensory evaluation, Experiment 4 chilled meat and frozen meat stored during 6 months were compared. The results did not indicate quality losses which could be organoleptically detected.” (Bustabad, 1999)
We have seen different factors that affect the rate and degree of weight loss during freezing and storage of meat.
- Surface/volume ratios such as in Beef FQ’s.
- Fat and skin coverings in pork results in lower weight loss than beef or derined primals.
- Storing meat in boxes and wrapping it in polyethylene bags (bags of less than 0.05 mm thickness is suggested). Too thick bags will negatively affect the freezing rate.
- Air temperature,
- Air velocity, increases the rate of cooling
- Relative humidity,
- Carcase weight
- Previously chilled meat
- Relative Humidity
Food Science Australia offers the following practical suggestions.
- Chill as rapidly as possible for the first few hours using low air temperature (~0ºC) and high velocity (approx. 1 m/s);
- Reduce the air velocity to below 0.5 m/s after 8 to 10 hours for beef;
- Install evaporator coils with adequate surface area and shallow depth;
- Utilise modulating back pressure control to ensure that the coil is at the highest possible temperature for the current load.
Bustabad, O. M.. 1999. Weight loss during freezing and the storage of frozen meat, Department of Chemistry Engineering, School of Chemistry Engineering, Higher Polytechnic Institute “Jose Antonio Echevarria”, Havana, Cuba, Received 3 November 1997; accepted 16 March 1999. Journal of Food Engineering 41 (1999) 1-11 Elsevier.
Campanone, L. A., Roche, L. A., Salvadori, V. O., Mascheroni, R. H.. 2002. Monitoring of Weight Losses in Meat Products during Freezing and Frozen Storage. Food Sci Tech Int 2002;8(4):229–238, Sage Publications, ISSN: 1082-0132, DOI: 10.1106/108201302028555
Food Science Australia. Evaporative weight losses during processing. Meat Technology Update 3
Van der Wal, P. G., Engel, B., Van Beek, T. A., Veerkamp, C. H.. Chilling pig carcasses: Effects on temperature, weight loss and ultimate meat quality. December 1995. Meat Science 40(2):193-202 DOI:10.1016/0309-1740(94)00029-7 Source:PubMed