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Effects of Ice Water Chilling on Flavor of Chicken
Effects of Ice Water Chilling on Flavor of Chicken ELDON L. PIPPEN AND A. A. KLOSE
Western Utilization Research Branch, Agricultural Research Service, United Stales Department of Agriculture, Albany 6, California (Received for publication February 22, 1955)
I
PROCEDURE
Source and Processing of Chickens. Tento twelve-week-old colored broilers, obtained alive from a commercial source, were sacrificed as required, scalded at 128°F., machine picked and eviscerated while warm. Additional experimental operations were then carried out on the freshly slaughtered carcasses. Unless cooked immediately, they were then bagged in polyethylene and held at - 10°F. until needed. Chilling Methods. Two chilling methods were used throughout the study and are hereafter referred to as "air chill" and
"ice water chill." Air chilling was carried out by storing the freshly killed, dressed and drawn carcass or part thereof, bagged in polyethylene, in a 39°F. cold room for the allotted period. For ice-water chilling, the freshly killed, dressed and drawn carcasses or parts thereof, were placed, unless otherwise specified, in large glass jars. Usually six half carcasses were chilled in each jar. Ice cubes were then added, followed by distilled water sufficient to cover the carcasses. Unless so stated, no means of agitation was used to circulate the ice water. Usually the icewater bath was made up of two parts of ice to one part of water and the ratio of weight of ice and water to chicken was 4. Following addition of the ice and water to the chicken, the jar was covered and placed in a cold room at 39°F. for the allotted times. When the chilling period was over, the chicken was removed from the ice water bath, drained, blotted, weighed, and bagged in polyethylene. These, together with corresponding halves which were air chilled, were, if not cooked immediately, stored at — 10°F. until needed. Cooking. Broth was prepared and served to judges as previously described by Pippen, Campbell and Streeter (1954). Weight of the fresh, eviscerated chicken observed prior to experimental treatment was used as a basis on which to calculate the amount of water needed to prepare comparable broths. To prepare for roasting, half carcasses were removed from — 10°F. storage, held (in polyetheylene bags) for 2 hours at
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N A previous study, Pippen, Campbell and Streeter (1954) showed that broth prepared from half carcasses immersed in ice water for as little as 5 hours had less flavor than broth from unsoaked halves. Since explanation for the flavor difference could not be found in existing reports on cold water chilling (Bailey, Stewart and Lowe, 1948; Roberts and Robertson, 1941) and since chilling freshly killed, ready-to-cook poultry by immersion in ice water is widely practiced, work was undertaken to determine the mechanism and extent of flavor loss, its chemical nature, and the practical importance of the effects on flavor. Data are presented that substantiate earlier preliminary findings, indicate the nature of substances leached by ice water, and demonstrate that loss of flavor by ice water chilling in the best commercial practice is not great enough to be of practical importance.
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Half Carcasses in Ice Water on Flavor of Broth. It had been shown (Pippen, Campbell and Streeter, 1954) that broth prepared from half carcasses that had been immersed for as little as 5 hours in ice water had less flavor than broth from unsoaked halves. These results were based on carcasses which had been previously frozen. It was therefore necessary to determine if the same effect could be observed on freshly slaughtered, unfrozen half carcasses. Eighteen carcasses were divided into 3 groups of 6. Chilling periods of 18, 8, and 3 hours duration were assigned to the groups. Carcasses were then split in two and within each group, six halves were air chilled during corresponding ice water chilling periods for the counterparts. Results of tasting broth from these are presented in Table 1. It is apparent from these data that half carcasses from freshly slaughtered unfrozen birds, when soaked for as little as three hours in ice water, have less ability to impart flavor to broth than unsoaked, air chilled halves. Demonstration of Presence of Flavoring Substance in Ice Water Used to Chill Half Carcasses. Since the taste panel consistently noted a difference in flavor of broth from half carcasses chilled by the two methods, it was of interest to ascertain the mechanism of flavor loss. It seemed likely that this was attributable to extraction of flavoring substances by cold TABLE 1.—Effect of chilling half carcasses [from freshly slaughtered, unfrozen birds) in ice water on flavor of broth Times ranked first Duration of chilling, hours 3 8 18
Air chill
Ice water chill
33 43 43
13 6 8
RESULTS AND DISCUSSION
Effect of Soaking Freshly Slaughtered
Differences between chilling methods are highly significant for all chilling periods.
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room temperature and then overnight at 40°F. Drip occurring during thawing was discarded. Halves were then roasted in a rotating stage oven until a thermometer inserted in the thick part of the breast muscle registered 180°F. When needed for frying, carcasses were removed from — 10°F., and sawed in two. Halves to be fried were then thawed as described above for roast chicken. Preliminary tests were made to establish optimum frying time based on the weight of the half carcass. Peanut oil was used at an initial temperature of 150°C. (302°F.), and maintained at 144°C. (291°F.) after immersion of the chicken. Halves were fried on racks and in separate kettles. Flavor Evaluation. For purposes of this study, flavor is defined as the stimuli produced by the sample on the taster's receptors, both oral and nasal, when the sample is consumed orally; odor is defined as the stimuli evoked when a sample is smelled {i.e. only volatile components reach the receptor of the judge). Flavor and odor evaluation were accomplished by a taste panel of seven individuals. Each judge evaluated each replicate from an experiment. In all cases, the judge was asked to rank the samples for intensity of chicken flavor, with a rank of 1 for the sample judged to have most intense chicken flavor, 2 for the next most intense, etc. Judges evaluating samples had previous experience in organoleptic evaluation of broth, fried and roast chicken. The latter were tasted as soon as possible following completion of roasting and frying. Muscle only was tasted and a judge received the corresponding cut each time. Significance of results was evaluated by appropriate methods of analysis, Snedecor (1946).
EFFECTS OF ICE WATER CHILLING ON FLAVOR
TABLE 2.—Ice water extraction of flavor from chicken half carcasses
Treatment prior to broth preparation
Average rank 1 for flavor intensity of broth
Ice water chilled, extract and drip recovered Air chilled, drip discarded Ice water chilled, extract and drip discarded
1.1 1.9 3.0
1
l=Highest intensity of flavor; 3 = lowest. Differences in rank between treatments were found to be highly significant. An 18 hour chilling time was used.
noted by the taste panel were highly significant we may conclude that, under the conditions used here, (a) ice water chilled half carcasses make less flavorful broth than air chilled half carcasses in confirmation of previous results, (b) extraction of flavoring substance is in fact responsible for flavor differences noted in broth from half carcasses chilled by the two methods and, (c) broth from the ice water chilled half carcasses with extract and drip losses recovered was more flavorful than that from the other two treatments. It was somewhat surprising that broth from the group where extract and drip losses were recovered was judged to be more flavorful than that from the air chilled group. It was postulated that this difference was due to either one or a combination of the following factors: (1) differences in drip losses on thawing and (2) soaking uncooked chicken in cold water may permit flavor precursors to diffuse out into the water which would ordinarily be trapped by heat induced changes when the meat is cooked. These factors were therefore investigated in the next experiment. Evaluation of Effect of Drip Losses and of Thawing in Cooking Water on Flavor of Broth. Eighteen half carcasses were randomized into 3 groups of 6 each. Halves
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water. To test this hypothesis, broth was prepared from half carcasses which had received the following treatments: (1) unsoaked or air chilled, drip (on thawing) discarded, (2) ice water chilled, cold water extract and drip (on thawing) recovered and added back, and (3) ice water chilled, cold water extract and drip (on thawing) discarded. Nine carcasses from freshly killed birds were split in two and the halves were separated randomly into 3 groups containing six halves each. Two groups were ice water chilled, in separate containers, for 18 hours. Halves in the remaining group were air chilled for 18 hours. Recovery of the substance extracted during ice water chilling was accomplished by filtering the ice water (remaining ice was melted and resulting water filtered) and subsequent removal of water from the filtrate (12 liters) by sublimation from the frozen state. The dry residue obtained weighed 11.0 g. and represents solids extracted by cold water from halves having a freshly killed weight of 2808 g. During the course of these experiments it was noticed that when frozen chicken was thawed, volume of "drip" from ice water chilled birds was much greater (about 3 times greater) than that from air chilled birds. Therefore drip from ice water chilled birds was considered as a part of the loss due to water extraction. This exudate from the three groups was separately collected as completely as possible. For the appropriate group (treatment 2, listed above) drip was added to the cooking water, along with extract recovered from the ice water. Drip from the other two groups was not added back on cooking; solids in them were recovered by freeze drying and used for analytical purposes. Results of tasting broth from six replicates of this experiment are shown in Table 2. Since differences between treatments
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TABLE 3.—Evaluation of drip loss and effect of thawing in cooking water on flavor of broth
Group No.
Treatment prior to broth preparation
1
Frozen, thawed in cooking water, drip recovered Frozen, thawed in air at 39°F., drip recovered Frozen, thawed in air at 39°F., drip discarded
2 3
Average rank 1 for flavor intensity 1.2 2.3 2.5
1 l=Highest intensity of flavor; 3 = lowest. L.S.D., 5%, 0.43, 1%, 0.60. Average ranks are based on 42 replications.
ing and thawing under the conditions used here, is not sufficient to be of importance to flavor of broth. On the other hand, more intensely flavored broth was obtained from half carcasses thawed in water that was subsequently used for cooking. This readily explains the problem posed in the previously described experiment, namely the more intense flavor of broth from the "ice water chilled, extract and drip recovered" group over that from the "air chilled, drip discarded" group. This result lends support to the theory that a pre-soak of the uncooked carcass in cold water, which is subsequently used for cooking, results in extraction of more flavor into the broth than the usual cooking procedure. Investigation of the Amount and Chemical Nature of Material Extracted from Half Carcasses During Ice Water Chilling. On the basis of the results, more information concerning the nature of the substance extracted during ice water chilling was desirable. Therefore solids present in ice water used to chill half carcasses were recovered in several instances by removing most of the water by distillation in vacuo and finishing by freeze-drying. Solids present in drip on thawing were similarly recovered since the quantity of drip is related to the chilling method used. Typical yields of dry extract and dry solids from drip together with pertinent experimental conditions are presented in Table 4. Actual weight loss due to the combined action of extraction and drip appears somewhat small when compared to the 3 kg. of chicken from which loss occurred. However, when it is realized that about 75% of the carcass weight is water and that of the remainder only approximately 20% is extracted into the broth (under conditions used in this study, broth containing about 4% solids was obtained) during cooking, it is readily seen that losses from
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were weighed immediately after splitting, bagged in polyethylene and stored overnight at 39°F. They were then frozen at — 10°F. For the thawing, halves were removed from the bag, while still solidly frozen and all groups were thawed 42 hours at 39°F. Group 1 was thawed by placing the halves in a stainless steel kettle to which was added distilled water equal to § of the freshly eviscerated weight of the chicken. As thawing proceeded, legs were cut off at the hip joint to permit more compact packing of the chicken in the container so that it would be totally immersed during thawing. The halves were subsequently cooked in this water in which they were thawed. Group 2 was thawed by placing the halves in a covered stainless steel kettle. Consequently drip from them collected in the kettle and was cooked along with the half carcasses. Group 3 was thawed by suspending the halves in a covered glass jar. Drip from them was collected in the bottom of the jar and was not cooked with the halves from which it originated. Solid material dissolved in the drip from this group amounted to 4.1 g. Before cooking, legs were separated at the hip joint for groups 2 and 3. Results of tasting broth from these groups is shown in Table 3. It is apparent that loss incurred through drip, when a half carcass undergoes freez-
EFFECTS OF ICE WATER CHILLING ON FLAVOR TABLE 4.—Typical loss of solids from air and ice water chilled half carcasses due to extraction by ice water and to drip during thawing (Results are based on half carcasses having a combined, fresh-killed weight of 3 kg. per experiment)
Chilling condition
Air, 18 hours Ice water, 18 hours
4
0.00 11.8
2.1 6.5
1.2 10.5
1 This calculation is based on the assumption that after three hours' cooking, the liquid phases in broth and carcass are in equilibrium.
extraction and drip can represent as much as 10% of the solids extractable from the carcass during cooking. Solids in extract and from drip were investigated further by analyzing them for nitrogen and ash. These results are summarized in Table 5. One of the most remarkable features of these results is the high percentage of ash in the extract. Ash content consistently amounted to about 33% of the solids recovered from ice water chilling baths. The possibility of a considerable contribution to the ash content by mineral impurities present in the water and ice used for chilling purposes was considered and ruled out when an experiment showed that the contribution from this source would be negligible. Relation of Mineral Content of Extract to Flavor. High ash content of the extract TABLE S.—Analysis of dry material recovered from drip on thawing and ice water used to chill half carcasses (Results are expressed on a moisture-free basis) Source of material analyzed
Total nitrogen
Drip From chilling water
13.99 9.36
Van Slyke nitrogen
% 1.49 1.73
Ash
% 9.8 33.7
suggested that this fraction, representing inorganic salts, might be largely responsible for flavor differences noted. To test this possibility, broth was prepared from 3 groups of half carcasses which had received the following treatments: (1) air chilled, (2) ice water chilled, and (3) ice water chilled with mineral content of the extract isolated and added back. Experimental details up to and including isolation of the ice water extract are the same as described above. To isolate minerals, the dry extract (12.2 g. from 2.6 kg. of chicken) was heated in a platinum dish until only a white ash remained. The ash, 4.0 g., was taken up in water and the alkaline solution, pH 11.8, was adjusted to pH 6.0 with 1 N HC1. The resulting mixture was warmed 15 minutes on a hot plate and then filtered. Insoluble matter on the filter amounted to only 0.1 g. when dry and was discarded. When chicken was cooked to prepare broth, the clear filtrate which contained components of the ash soluble at pH 6.0, was added along with necessary additional water for cooking, to that group of chicken from which it had originated. Data obtained from evaluation of 6 replications of this experiment (Table 6) show that most of TABLE 6.—Effect of reincorporation of minerals present in the ice water extract on flavor of broth Average rank for flavor intensity 1 Treatment prior to broth preparation
Ash neutralized with hydrochloric acid2
Ash neutralized with carbon dioxide3
Air chill Ice water chill plus ashed extract Ice water chill
1.4
1.7
1.6 3.0
1.4 2.9
1
1 = highest flavor intensity; 3 = lowest. L.S.D., 5% 0.30; 1% 0.38. 3 L.S.D., 5% 0.33; 1% 0.41. 2
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Percentage of broth solids which Solids Solids Ratio may be extracted present of ice in drip on during lost water to chilling, thawing, due to chicken water exg. gtraction and drip on thawing 1
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the flavor lost during ice water chilling ride were present in considerable amount. was restored by adding back the HC1 While these results show that sufficient neutralized ash of the extract. mineral flavoring components are exIn the experiment just described, neu- tracted during ice water chilling of half tralization of the ash with hydrochloric carcasses to affect taste of broth, other acid resulted in formation of chloride components necessary for development of salts not originally present. It seemed pos- characteristic chicken flavor are exsible, therefore, that the effectiveness of tracted to an appreciable extent only the ash in flavor restoration could be in under conditions more ideal for extracpart due to this added chloride rather tion (Pippen, Campbell and Streeter, than alone to minerals originally present. 1954). To rule out this complicating factor as far Feasibility of Restoring Lost Flavor with as possible, an experiment was conducted Sodium Chloride. On the basis of results in which CO2 was used to neutralize the just described it seemed likely that subash. The ice water bath extracted 9.7 g. of stitution of sodium chloride for material soluble solids, containing 34.2% ash, extracted might restore part or all of the' from 3.0 kg. of chicken. The ash was flavor. This was tested by repeating the taken up in distilled water, and the al- above-described experiment up to and inkaline (pH 12) mixture was brought to pH cluding isolation of the extract. The re7.0 by bubbling C0 2 into it. Filtration re- covered, dry extract amounted to 17.4 g. sulted in a clear filtrate and an insoluble from half carcasses having a freshly residue which was again extracted with killed weight of 2759 g. Since, as reported water and CO2. A small insoluble residue, above, it had been found that these exweighing 0.2 g. was discarded. The clear tracts analyzed at about 33% ash, onenitrates were incorporated in the water third of the extract weight or 5.8 g. of used to cook the chicken from which the sodium chloride was added, just prior to ash had originated. Results of evaluating cooking, to the group from which the exthe three categories of broth obtained tract had been recovered. This would from this experiment are shown in Table amount to a sodium chloride concentra6. Again the ability of the neutralized ash tion of 0.15% (w/w) in the broth based to restore lost flavor is noted showing that on the amount of water added for cooking minerals originally present are respon- plus an assumed water content of 75% in sible. Thus, flavor differences noted in the chicken. There was thus obtained, for this study are primarily associated with organoleptic comparison, broth prepared the mineral fraction of the material ex- from the following groups of half cartracted during ice water chilling. It is ap- casses: (1) air chilled, (2) ice water chilled parent that this mineral fraction makes plus sodium chloride, and (3) ice water its principal contribution to taste by chilled. Results of evaluating 4 replicacontributing to saltiness. This conclusion tions of these broth samples (Table 7) is supported by observing that aqueous show that part but not all of the lost solutions of either HC1 or CO2 neutralized flavor was restored to the sample to which ash had a salty taste, that part of the lost salt had been added. flavor could be restored by addition of Flavor of Roast Chicken Prepared from sodium chloride, as shown below, and by Air Chilled and Ice Water Chilled Half analysis of the ashed extract which Carcasses. Eighteen carcasses were dishowed that potassium, sodium, and chlovided into three equal groups. Chilling
EFFECTS OF ICE WATER CHILLING ON FLAVOR TABLE 7.—Effect on flavor of broth of substituting sodium chloride equivalent to weight of minerals extracted during ice water chilling Average rank 1 for flavor intensity
Treatment prior to broth preparation
1.3 1.7 3.0
Air chilled, no salt added Ice water chilled, salt added Ice water chilled, no salt added
periods of 18, 8, and 3 hours duration were assigned to the groups. Each carcass was then cut in two lengthwise and within each group six halves were air chilled while corresponding counterparts were ice water chilled. After chilling, halves were stored at — 10°F. until removed for roasting. Thawing and roasting procedure are described above under the section on cooking. Data from organoleptic evaluation of intensity of chicken flavor in the roasted halves for 3 chilling periods are shown in Table 8. Results were analyzed for light and dark meat together, for light meat only and for dark meat only. It is clear from these results that for all chilling times there was a trend showing preference for the air chilled over ice water TABLE 8.—Evaluation of flavor intensity in roasted chicken prepared from half carcasses which had been air and ice water chilled Times ranked first Type and duration of chill
Light and dark meat
Light meat only
Dark meat only
3 hour air 3 hour ice water
24 16
10 6
14 10
8 hour air 8 hour ice water
24 13
12 2*
12 11
18 hour air 18 hour ice water
32 6*
14 2*
18 4*
* Difference is significant at the 1% level. Other differences are not significant.
chilled, but that the difference was significant for both dark and light meat only for the longest chilling time employed. We may speculate that exposure of the breast muscle, which occurs when the carcass is cut in two, is responsible for significant loss of flavor in the light meat during an 8 hour ice water chill whereas the dark meat, covered by a still more or less intact layer of skin, suffers no detectable flavor loss during the same period of immersion in ice water. Air Chilled Versus Ice Water Chilled Whole Carcasses. Previous experiments reported here were based on use of half carcasses because this made it possible to eliminate bird-to-bird flavor variation as a possible source of error. Commercially, however, most poultry is chilled in the whole carcass form. The study was therefore extended to determine to what extent results obtained on halves would also apply to whole carcasses. In these experiments, ice water chilling was carried out in a large commercial type holding tank which was equipped with an agitator. Efficiency of agitation and ratio of weight of ice water to weight of chicken were considered equal to or greater than that usually found in industry. When removed from the chilling tank, carcasses were permitted to drain 15 minutes. Air chilling was accomplished as described above for half carcasses. Results were obtained for broth, roasted and fried chicken and are presented in Table 9. Examination of the data show that results of flavor evaluation of broth and roasted chicken prepared from the whole carcasses are similar to those noted for half carcasses. On the other hand, results show no difference in flavor of subsequently fried chicken which had been chilled by the two methods. Definite reasons as to why the panel was able to detect a difference between roasted but
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1 l=Highest intensity of flavor; 3=lowest. L.S.D., 1% level, 0.38. Chilling period: 18 hours.
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TABLE 9.—Comparison of ice water chilling versus air chilling of whole chicken carcasses for their effect on flivor of broth, roasted meat, and fried meat
Material evaluated
Duration of chill, hours
Times ranked first for flavor intensity Air chill
Ice water chill
3 8 20
43 44 46
9 0 2
Roasted chicken
8 20
21 28
12 7
Fried chicken
4 20
20 21
19 20
Significance of differences: Broth—Significant at the 1% level for all chilling times. Roasted Chicken—Significant at the 1% level for the 20 hour period; not significant for the 8 hour period. Fried Chicken—Not significant for either chilling period.
not fried chicken which had been chilled by the two methods for 20 hours are not apparent. The explanation may lie in inherent differences between the cooking methods with respect to time, temperature, etc. as related to flavor development. SUMMARY AND CONCLUSIONS
ACKNOWLED GMENT
A study was undertaken to determine the effects of ice water chilling on the flavor of chicken. Aspects investigated included the mechanism, extent, chemical nature and practical importance of flavor changes resulting from ice water chilling. Broth prepared from half carcasses immersed in ice water for as little as 3 hours had significantly less flavor than broth from unsoaked halves. Recovery and reincorporation of material extracted from the chicken during ice water chilling restored lost flavor. Considerable restoration of flavor was also obtained by adding back the neutralized ash of the extract,
The authors wish to thank A. A. Campbell for carrying out organoleptic evaluation needed for this work. REFERENCES Bailey, R. L., G. F. Stewart and B. Lowe, 1948. Ice slush cooling of dressed poultry. Refrig. Eng. 55: 369-371. Pippen, E. L., A. A. Campbell and I. V. Streeter, 1954. Flavor studies. Origin of chicken flavor. J. Ag. Food Chem. 2: 364-367. Roberts, J., and E. I. Robertson, 1941. A comparison of wet and dry cooling of dressed poultry. Bull. No. 403, State College of Washington, Agricultural Experiment Station, Pullman, Washington. Snedecor, G. W., 1946. Statistical Methods, Iowa State College Press, Ames. Iowa.
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Chicken broth
indicating that ability of the extract to restore flavor is associated with its mineral content. Substitution of sodium chloride equivalent in weight to minerals extracted restored part but not all of the flavor. In contrast to results on broth, half and whole carcasses immersed for 3 hours in ice water, and subsequently roasted, did not differ significantly in flavor from air chilled counterparts. When the chilling time was increased to 18 hours, there was a significant difference between flavor of air chilled and ice water chilled roasted chicken. There was no detectable loss of flavor in the subsequently fried chicken, when whole carcasses were chilled in ice water for 20 hours. It is concluded that prolonged holding of chicken in cold water is deleterious to the maintenance of optimum flavor and should be avoided. On the other hand, results indicate that ice-slush chilling of whole, ready-to-cook chicken carcasses, as normally practiced in industry, does not result in detectable loss of flavor in the fried or roasted product.
Western Utilization Research Branch, Agricultural Research Service, United Stales Department of Agriculture, Albany 6, California (Received for publication February 22, 1955)
I
PROCEDURE
Source and Processing of Chickens. Tento twelve-week-old colored broilers, obtained alive from a commercial source, were sacrificed as required, scalded at 128°F., machine picked and eviscerated while warm. Additional experimental operations were then carried out on the freshly slaughtered carcasses. Unless cooked immediately, they were then bagged in polyethylene and held at - 10°F. until needed. Chilling Methods. Two chilling methods were used throughout the study and are hereafter referred to as "air chill" and
"ice water chill." Air chilling was carried out by storing the freshly killed, dressed and drawn carcass or part thereof, bagged in polyethylene, in a 39°F. cold room for the allotted period. For ice-water chilling, the freshly killed, dressed and drawn carcasses or parts thereof, were placed, unless otherwise specified, in large glass jars. Usually six half carcasses were chilled in each jar. Ice cubes were then added, followed by distilled water sufficient to cover the carcasses. Unless so stated, no means of agitation was used to circulate the ice water. Usually the icewater bath was made up of two parts of ice to one part of water and the ratio of weight of ice and water to chicken was 4. Following addition of the ice and water to the chicken, the jar was covered and placed in a cold room at 39°F. for the allotted times. When the chilling period was over, the chicken was removed from the ice water bath, drained, blotted, weighed, and bagged in polyethylene. These, together with corresponding halves which were air chilled, were, if not cooked immediately, stored at — 10°F. until needed. Cooking. Broth was prepared and served to judges as previously described by Pippen, Campbell and Streeter (1954). Weight of the fresh, eviscerated chicken observed prior to experimental treatment was used as a basis on which to calculate the amount of water needed to prepare comparable broths. To prepare for roasting, half carcasses were removed from — 10°F. storage, held (in polyetheylene bags) for 2 hours at
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N A previous study, Pippen, Campbell and Streeter (1954) showed that broth prepared from half carcasses immersed in ice water for as little as 5 hours had less flavor than broth from unsoaked halves. Since explanation for the flavor difference could not be found in existing reports on cold water chilling (Bailey, Stewart and Lowe, 1948; Roberts and Robertson, 1941) and since chilling freshly killed, ready-to-cook poultry by immersion in ice water is widely practiced, work was undertaken to determine the mechanism and extent of flavor loss, its chemical nature, and the practical importance of the effects on flavor. Data are presented that substantiate earlier preliminary findings, indicate the nature of substances leached by ice water, and demonstrate that loss of flavor by ice water chilling in the best commercial practice is not great enough to be of practical importance.
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Half Carcasses in Ice Water on Flavor of Broth. It had been shown (Pippen, Campbell and Streeter, 1954) that broth prepared from half carcasses that had been immersed for as little as 5 hours in ice water had less flavor than broth from unsoaked halves. These results were based on carcasses which had been previously frozen. It was therefore necessary to determine if the same effect could be observed on freshly slaughtered, unfrozen half carcasses. Eighteen carcasses were divided into 3 groups of 6. Chilling periods of 18, 8, and 3 hours duration were assigned to the groups. Carcasses were then split in two and within each group, six halves were air chilled during corresponding ice water chilling periods for the counterparts. Results of tasting broth from these are presented in Table 1. It is apparent from these data that half carcasses from freshly slaughtered unfrozen birds, when soaked for as little as three hours in ice water, have less ability to impart flavor to broth than unsoaked, air chilled halves. Demonstration of Presence of Flavoring Substance in Ice Water Used to Chill Half Carcasses. Since the taste panel consistently noted a difference in flavor of broth from half carcasses chilled by the two methods, it was of interest to ascertain the mechanism of flavor loss. It seemed likely that this was attributable to extraction of flavoring substances by cold TABLE 1.—Effect of chilling half carcasses [from freshly slaughtered, unfrozen birds) in ice water on flavor of broth Times ranked first Duration of chilling, hours 3 8 18
Air chill
Ice water chill
33 43 43
13 6 8
RESULTS AND DISCUSSION
Effect of Soaking Freshly Slaughtered
Differences between chilling methods are highly significant for all chilling periods.
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room temperature and then overnight at 40°F. Drip occurring during thawing was discarded. Halves were then roasted in a rotating stage oven until a thermometer inserted in the thick part of the breast muscle registered 180°F. When needed for frying, carcasses were removed from — 10°F., and sawed in two. Halves to be fried were then thawed as described above for roast chicken. Preliminary tests were made to establish optimum frying time based on the weight of the half carcass. Peanut oil was used at an initial temperature of 150°C. (302°F.), and maintained at 144°C. (291°F.) after immersion of the chicken. Halves were fried on racks and in separate kettles. Flavor Evaluation. For purposes of this study, flavor is defined as the stimuli produced by the sample on the taster's receptors, both oral and nasal, when the sample is consumed orally; odor is defined as the stimuli evoked when a sample is smelled {i.e. only volatile components reach the receptor of the judge). Flavor and odor evaluation were accomplished by a taste panel of seven individuals. Each judge evaluated each replicate from an experiment. In all cases, the judge was asked to rank the samples for intensity of chicken flavor, with a rank of 1 for the sample judged to have most intense chicken flavor, 2 for the next most intense, etc. Judges evaluating samples had previous experience in organoleptic evaluation of broth, fried and roast chicken. The latter were tasted as soon as possible following completion of roasting and frying. Muscle only was tasted and a judge received the corresponding cut each time. Significance of results was evaluated by appropriate methods of analysis, Snedecor (1946).
EFFECTS OF ICE WATER CHILLING ON FLAVOR
TABLE 2.—Ice water extraction of flavor from chicken half carcasses
Treatment prior to broth preparation
Average rank 1 for flavor intensity of broth
Ice water chilled, extract and drip recovered Air chilled, drip discarded Ice water chilled, extract and drip discarded
1.1 1.9 3.0
1
l=Highest intensity of flavor; 3 = lowest. Differences in rank between treatments were found to be highly significant. An 18 hour chilling time was used.
noted by the taste panel were highly significant we may conclude that, under the conditions used here, (a) ice water chilled half carcasses make less flavorful broth than air chilled half carcasses in confirmation of previous results, (b) extraction of flavoring substance is in fact responsible for flavor differences noted in broth from half carcasses chilled by the two methods and, (c) broth from the ice water chilled half carcasses with extract and drip losses recovered was more flavorful than that from the other two treatments. It was somewhat surprising that broth from the group where extract and drip losses were recovered was judged to be more flavorful than that from the air chilled group. It was postulated that this difference was due to either one or a combination of the following factors: (1) differences in drip losses on thawing and (2) soaking uncooked chicken in cold water may permit flavor precursors to diffuse out into the water which would ordinarily be trapped by heat induced changes when the meat is cooked. These factors were therefore investigated in the next experiment. Evaluation of Effect of Drip Losses and of Thawing in Cooking Water on Flavor of Broth. Eighteen half carcasses were randomized into 3 groups of 6 each. Halves
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water. To test this hypothesis, broth was prepared from half carcasses which had received the following treatments: (1) unsoaked or air chilled, drip (on thawing) discarded, (2) ice water chilled, cold water extract and drip (on thawing) recovered and added back, and (3) ice water chilled, cold water extract and drip (on thawing) discarded. Nine carcasses from freshly killed birds were split in two and the halves were separated randomly into 3 groups containing six halves each. Two groups were ice water chilled, in separate containers, for 18 hours. Halves in the remaining group were air chilled for 18 hours. Recovery of the substance extracted during ice water chilling was accomplished by filtering the ice water (remaining ice was melted and resulting water filtered) and subsequent removal of water from the filtrate (12 liters) by sublimation from the frozen state. The dry residue obtained weighed 11.0 g. and represents solids extracted by cold water from halves having a freshly killed weight of 2808 g. During the course of these experiments it was noticed that when frozen chicken was thawed, volume of "drip" from ice water chilled birds was much greater (about 3 times greater) than that from air chilled birds. Therefore drip from ice water chilled birds was considered as a part of the loss due to water extraction. This exudate from the three groups was separately collected as completely as possible. For the appropriate group (treatment 2, listed above) drip was added to the cooking water, along with extract recovered from the ice water. Drip from the other two groups was not added back on cooking; solids in them were recovered by freeze drying and used for analytical purposes. Results of tasting broth from six replicates of this experiment are shown in Table 2. Since differences between treatments
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TABLE 3.—Evaluation of drip loss and effect of thawing in cooking water on flavor of broth
Group No.
Treatment prior to broth preparation
1
Frozen, thawed in cooking water, drip recovered Frozen, thawed in air at 39°F., drip recovered Frozen, thawed in air at 39°F., drip discarded
2 3
Average rank 1 for flavor intensity 1.2 2.3 2.5
1 l=Highest intensity of flavor; 3 = lowest. L.S.D., 5%, 0.43, 1%, 0.60. Average ranks are based on 42 replications.
ing and thawing under the conditions used here, is not sufficient to be of importance to flavor of broth. On the other hand, more intensely flavored broth was obtained from half carcasses thawed in water that was subsequently used for cooking. This readily explains the problem posed in the previously described experiment, namely the more intense flavor of broth from the "ice water chilled, extract and drip recovered" group over that from the "air chilled, drip discarded" group. This result lends support to the theory that a pre-soak of the uncooked carcass in cold water, which is subsequently used for cooking, results in extraction of more flavor into the broth than the usual cooking procedure. Investigation of the Amount and Chemical Nature of Material Extracted from Half Carcasses During Ice Water Chilling. On the basis of the results, more information concerning the nature of the substance extracted during ice water chilling was desirable. Therefore solids present in ice water used to chill half carcasses were recovered in several instances by removing most of the water by distillation in vacuo and finishing by freeze-drying. Solids present in drip on thawing were similarly recovered since the quantity of drip is related to the chilling method used. Typical yields of dry extract and dry solids from drip together with pertinent experimental conditions are presented in Table 4. Actual weight loss due to the combined action of extraction and drip appears somewhat small when compared to the 3 kg. of chicken from which loss occurred. However, when it is realized that about 75% of the carcass weight is water and that of the remainder only approximately 20% is extracted into the broth (under conditions used in this study, broth containing about 4% solids was obtained) during cooking, it is readily seen that losses from
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were weighed immediately after splitting, bagged in polyethylene and stored overnight at 39°F. They were then frozen at — 10°F. For the thawing, halves were removed from the bag, while still solidly frozen and all groups were thawed 42 hours at 39°F. Group 1 was thawed by placing the halves in a stainless steel kettle to which was added distilled water equal to § of the freshly eviscerated weight of the chicken. As thawing proceeded, legs were cut off at the hip joint to permit more compact packing of the chicken in the container so that it would be totally immersed during thawing. The halves were subsequently cooked in this water in which they were thawed. Group 2 was thawed by placing the halves in a covered stainless steel kettle. Consequently drip from them collected in the kettle and was cooked along with the half carcasses. Group 3 was thawed by suspending the halves in a covered glass jar. Drip from them was collected in the bottom of the jar and was not cooked with the halves from which it originated. Solid material dissolved in the drip from this group amounted to 4.1 g. Before cooking, legs were separated at the hip joint for groups 2 and 3. Results of tasting broth from these groups is shown in Table 3. It is apparent that loss incurred through drip, when a half carcass undergoes freez-
EFFECTS OF ICE WATER CHILLING ON FLAVOR TABLE 4.—Typical loss of solids from air and ice water chilled half carcasses due to extraction by ice water and to drip during thawing (Results are based on half carcasses having a combined, fresh-killed weight of 3 kg. per experiment)
Chilling condition
Air, 18 hours Ice water, 18 hours
4
0.00 11.8
2.1 6.5
1.2 10.5
1 This calculation is based on the assumption that after three hours' cooking, the liquid phases in broth and carcass are in equilibrium.
extraction and drip can represent as much as 10% of the solids extractable from the carcass during cooking. Solids in extract and from drip were investigated further by analyzing them for nitrogen and ash. These results are summarized in Table 5. One of the most remarkable features of these results is the high percentage of ash in the extract. Ash content consistently amounted to about 33% of the solids recovered from ice water chilling baths. The possibility of a considerable contribution to the ash content by mineral impurities present in the water and ice used for chilling purposes was considered and ruled out when an experiment showed that the contribution from this source would be negligible. Relation of Mineral Content of Extract to Flavor. High ash content of the extract TABLE S.—Analysis of dry material recovered from drip on thawing and ice water used to chill half carcasses (Results are expressed on a moisture-free basis) Source of material analyzed
Total nitrogen
Drip From chilling water
13.99 9.36
Van Slyke nitrogen
% 1.49 1.73
Ash
% 9.8 33.7
suggested that this fraction, representing inorganic salts, might be largely responsible for flavor differences noted. To test this possibility, broth was prepared from 3 groups of half carcasses which had received the following treatments: (1) air chilled, (2) ice water chilled, and (3) ice water chilled with mineral content of the extract isolated and added back. Experimental details up to and including isolation of the ice water extract are the same as described above. To isolate minerals, the dry extract (12.2 g. from 2.6 kg. of chicken) was heated in a platinum dish until only a white ash remained. The ash, 4.0 g., was taken up in water and the alkaline solution, pH 11.8, was adjusted to pH 6.0 with 1 N HC1. The resulting mixture was warmed 15 minutes on a hot plate and then filtered. Insoluble matter on the filter amounted to only 0.1 g. when dry and was discarded. When chicken was cooked to prepare broth, the clear filtrate which contained components of the ash soluble at pH 6.0, was added along with necessary additional water for cooking, to that group of chicken from which it had originated. Data obtained from evaluation of 6 replications of this experiment (Table 6) show that most of TABLE 6.—Effect of reincorporation of minerals present in the ice water extract on flavor of broth Average rank for flavor intensity 1 Treatment prior to broth preparation
Ash neutralized with hydrochloric acid2
Ash neutralized with carbon dioxide3
Air chill Ice water chill plus ashed extract Ice water chill
1.4
1.7
1.6 3.0
1.4 2.9
1
1 = highest flavor intensity; 3 = lowest. L.S.D., 5% 0.30; 1% 0.38. 3 L.S.D., 5% 0.33; 1% 0.41. 2
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Percentage of broth solids which Solids Solids Ratio may be extracted present of ice in drip on during lost water to chilling, thawing, due to chicken water exg. gtraction and drip on thawing 1
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the flavor lost during ice water chilling ride were present in considerable amount. was restored by adding back the HC1 While these results show that sufficient neutralized ash of the extract. mineral flavoring components are exIn the experiment just described, neu- tracted during ice water chilling of half tralization of the ash with hydrochloric carcasses to affect taste of broth, other acid resulted in formation of chloride components necessary for development of salts not originally present. It seemed pos- characteristic chicken flavor are exsible, therefore, that the effectiveness of tracted to an appreciable extent only the ash in flavor restoration could be in under conditions more ideal for extracpart due to this added chloride rather tion (Pippen, Campbell and Streeter, than alone to minerals originally present. 1954). To rule out this complicating factor as far Feasibility of Restoring Lost Flavor with as possible, an experiment was conducted Sodium Chloride. On the basis of results in which CO2 was used to neutralize the just described it seemed likely that subash. The ice water bath extracted 9.7 g. of stitution of sodium chloride for material soluble solids, containing 34.2% ash, extracted might restore part or all of the' from 3.0 kg. of chicken. The ash was flavor. This was tested by repeating the taken up in distilled water, and the al- above-described experiment up to and inkaline (pH 12) mixture was brought to pH cluding isolation of the extract. The re7.0 by bubbling C0 2 into it. Filtration re- covered, dry extract amounted to 17.4 g. sulted in a clear filtrate and an insoluble from half carcasses having a freshly residue which was again extracted with killed weight of 2759 g. Since, as reported water and CO2. A small insoluble residue, above, it had been found that these exweighing 0.2 g. was discarded. The clear tracts analyzed at about 33% ash, onenitrates were incorporated in the water third of the extract weight or 5.8 g. of used to cook the chicken from which the sodium chloride was added, just prior to ash had originated. Results of evaluating cooking, to the group from which the exthe three categories of broth obtained tract had been recovered. This would from this experiment are shown in Table amount to a sodium chloride concentra6. Again the ability of the neutralized ash tion of 0.15% (w/w) in the broth based to restore lost flavor is noted showing that on the amount of water added for cooking minerals originally present are respon- plus an assumed water content of 75% in sible. Thus, flavor differences noted in the chicken. There was thus obtained, for this study are primarily associated with organoleptic comparison, broth prepared the mineral fraction of the material ex- from the following groups of half cartracted during ice water chilling. It is ap- casses: (1) air chilled, (2) ice water chilled parent that this mineral fraction makes plus sodium chloride, and (3) ice water its principal contribution to taste by chilled. Results of evaluating 4 replicacontributing to saltiness. This conclusion tions of these broth samples (Table 7) is supported by observing that aqueous show that part but not all of the lost solutions of either HC1 or CO2 neutralized flavor was restored to the sample to which ash had a salty taste, that part of the lost salt had been added. flavor could be restored by addition of Flavor of Roast Chicken Prepared from sodium chloride, as shown below, and by Air Chilled and Ice Water Chilled Half analysis of the ashed extract which Carcasses. Eighteen carcasses were dishowed that potassium, sodium, and chlovided into three equal groups. Chilling
EFFECTS OF ICE WATER CHILLING ON FLAVOR TABLE 7.—Effect on flavor of broth of substituting sodium chloride equivalent to weight of minerals extracted during ice water chilling Average rank 1 for flavor intensity
Treatment prior to broth preparation
1.3 1.7 3.0
Air chilled, no salt added Ice water chilled, salt added Ice water chilled, no salt added
periods of 18, 8, and 3 hours duration were assigned to the groups. Each carcass was then cut in two lengthwise and within each group six halves were air chilled while corresponding counterparts were ice water chilled. After chilling, halves were stored at — 10°F. until removed for roasting. Thawing and roasting procedure are described above under the section on cooking. Data from organoleptic evaluation of intensity of chicken flavor in the roasted halves for 3 chilling periods are shown in Table 8. Results were analyzed for light and dark meat together, for light meat only and for dark meat only. It is clear from these results that for all chilling times there was a trend showing preference for the air chilled over ice water TABLE 8.—Evaluation of flavor intensity in roasted chicken prepared from half carcasses which had been air and ice water chilled Times ranked first Type and duration of chill
Light and dark meat
Light meat only
Dark meat only
3 hour air 3 hour ice water
24 16
10 6
14 10
8 hour air 8 hour ice water
24 13
12 2*
12 11
18 hour air 18 hour ice water
32 6*
14 2*
18 4*
* Difference is significant at the 1% level. Other differences are not significant.
chilled, but that the difference was significant for both dark and light meat only for the longest chilling time employed. We may speculate that exposure of the breast muscle, which occurs when the carcass is cut in two, is responsible for significant loss of flavor in the light meat during an 8 hour ice water chill whereas the dark meat, covered by a still more or less intact layer of skin, suffers no detectable flavor loss during the same period of immersion in ice water. Air Chilled Versus Ice Water Chilled Whole Carcasses. Previous experiments reported here were based on use of half carcasses because this made it possible to eliminate bird-to-bird flavor variation as a possible source of error. Commercially, however, most poultry is chilled in the whole carcass form. The study was therefore extended to determine to what extent results obtained on halves would also apply to whole carcasses. In these experiments, ice water chilling was carried out in a large commercial type holding tank which was equipped with an agitator. Efficiency of agitation and ratio of weight of ice water to weight of chicken were considered equal to or greater than that usually found in industry. When removed from the chilling tank, carcasses were permitted to drain 15 minutes. Air chilling was accomplished as described above for half carcasses. Results were obtained for broth, roasted and fried chicken and are presented in Table 9. Examination of the data show that results of flavor evaluation of broth and roasted chicken prepared from the whole carcasses are similar to those noted for half carcasses. On the other hand, results show no difference in flavor of subsequently fried chicken which had been chilled by the two methods. Definite reasons as to why the panel was able to detect a difference between roasted but
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1 l=Highest intensity of flavor; 3=lowest. L.S.D., 1% level, 0.38. Chilling period: 18 hours.
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TABLE 9.—Comparison of ice water chilling versus air chilling of whole chicken carcasses for their effect on flivor of broth, roasted meat, and fried meat
Material evaluated
Duration of chill, hours
Times ranked first for flavor intensity Air chill
Ice water chill
3 8 20
43 44 46
9 0 2
Roasted chicken
8 20
21 28
12 7
Fried chicken
4 20
20 21
19 20
Significance of differences: Broth—Significant at the 1% level for all chilling times. Roasted Chicken—Significant at the 1% level for the 20 hour period; not significant for the 8 hour period. Fried Chicken—Not significant for either chilling period.
not fried chicken which had been chilled by the two methods for 20 hours are not apparent. The explanation may lie in inherent differences between the cooking methods with respect to time, temperature, etc. as related to flavor development. SUMMARY AND CONCLUSIONS
ACKNOWLED GMENT
A study was undertaken to determine the effects of ice water chilling on the flavor of chicken. Aspects investigated included the mechanism, extent, chemical nature and practical importance of flavor changes resulting from ice water chilling. Broth prepared from half carcasses immersed in ice water for as little as 3 hours had significantly less flavor than broth from unsoaked halves. Recovery and reincorporation of material extracted from the chicken during ice water chilling restored lost flavor. Considerable restoration of flavor was also obtained by adding back the neutralized ash of the extract,
The authors wish to thank A. A. Campbell for carrying out organoleptic evaluation needed for this work. REFERENCES Bailey, R. L., G. F. Stewart and B. Lowe, 1948. Ice slush cooling of dressed poultry. Refrig. Eng. 55: 369-371. Pippen, E. L., A. A. Campbell and I. V. Streeter, 1954. Flavor studies. Origin of chicken flavor. J. Ag. Food Chem. 2: 364-367. Roberts, J., and E. I. Robertson, 1941. A comparison of wet and dry cooling of dressed poultry. Bull. No. 403, State College of Washington, Agricultural Experiment Station, Pullman, Washington. Snedecor, G. W., 1946. Statistical Methods, Iowa State College Press, Ames. Iowa.
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Chicken broth
indicating that ability of the extract to restore flavor is associated with its mineral content. Substitution of sodium chloride equivalent in weight to minerals extracted restored part but not all of the flavor. In contrast to results on broth, half and whole carcasses immersed for 3 hours in ice water, and subsequently roasted, did not differ significantly in flavor from air chilled counterparts. When the chilling time was increased to 18 hours, there was a significant difference between flavor of air chilled and ice water chilled roasted chicken. There was no detectable loss of flavor in the subsequently fried chicken, when whole carcasses were chilled in ice water for 20 hours. It is concluded that prolonged holding of chicken in cold water is deleterious to the maintenance of optimum flavor and should be avoided. On the other hand, results indicate that ice-slush chilling of whole, ready-to-cook chicken carcasses, as normally practiced in industry, does not result in detectable loss of flavor in the fried or roasted product.